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-rw-r--r--third_party/abseil_cpp/absl/debugging/BUILD.bazel341
-rw-r--r--third_party/abseil_cpp/absl/debugging/CMakeLists.txt333
-rw-r--r--third_party/abseil_cpp/absl/debugging/failure_signal_handler.cc370
-rw-r--r--third_party/abseil_cpp/absl/debugging/failure_signal_handler.h121
-rw-r--r--third_party/abseil_cpp/absl/debugging/failure_signal_handler_test.cc159
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc138
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/address_is_readable.h32
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/demangle.cc1895
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/demangle.h71
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/demangle_test.cc195
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.cc382
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.h134
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/examine_stack.cc157
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/examine_stack.h42
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stack_consumption.cc184
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stack_consumption.h49
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stack_consumption_test.cc50
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_aarch64-inl.inc196
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_arm-inl.inc134
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_config.h70
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_generic-inl.inc108
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_powerpc-inl.inc248
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_unimplemented-inl.inc24
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_win32-inl.inc93
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/stacktrace_x86-inl.inc346
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/symbolize.h128
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/vdso_support.cc194
-rw-r--r--third_party/abseil_cpp/absl/debugging/internal/vdso_support.h158
-rw-r--r--third_party/abseil_cpp/absl/debugging/leak_check.cc53
-rw-r--r--third_party/abseil_cpp/absl/debugging/leak_check.h113
-rw-r--r--third_party/abseil_cpp/absl/debugging/leak_check_disable.cc20
-rw-r--r--third_party/abseil_cpp/absl/debugging/leak_check_fail_test.cc41
-rw-r--r--third_party/abseil_cpp/absl/debugging/leak_check_test.cc42
-rw-r--r--third_party/abseil_cpp/absl/debugging/stacktrace.cc140
-rw-r--r--third_party/abseil_cpp/absl/debugging/stacktrace.h231
-rw-r--r--third_party/abseil_cpp/absl/debugging/symbolize.cc25
-rw-r--r--third_party/abseil_cpp/absl/debugging/symbolize.h99
-rw-r--r--third_party/abseil_cpp/absl/debugging/symbolize_elf.inc1482
-rw-r--r--third_party/abseil_cpp/absl/debugging/symbolize_test.cc551
-rw-r--r--third_party/abseil_cpp/absl/debugging/symbolize_unimplemented.inc40
-rw-r--r--third_party/abseil_cpp/absl/debugging/symbolize_win32.inc81
41 files changed, 9270 insertions, 0 deletions
diff --git a/third_party/abseil_cpp/absl/debugging/BUILD.bazel b/third_party/abseil_cpp/absl/debugging/BUILD.bazel
new file mode 100644
index 000000000000..8f521bec4692
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/BUILD.bazel
@@ -0,0 +1,341 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
+load(
+    "//absl:copts/configure_copts.bzl",
+    "ABSL_DEFAULT_COPTS",
+    "ABSL_DEFAULT_LINKOPTS",
+    "ABSL_TEST_COPTS",
+)
+
+package(
+    default_visibility = ["//visibility:public"],
+)
+
+licenses(["notice"])  # Apache 2.0
+
+cc_library(
+    name = "stacktrace",
+    srcs = [
+        "internal/stacktrace_aarch64-inl.inc",
+        "internal/stacktrace_arm-inl.inc",
+        "internal/stacktrace_config.h",
+        "internal/stacktrace_generic-inl.inc",
+        "internal/stacktrace_powerpc-inl.inc",
+        "internal/stacktrace_unimplemented-inl.inc",
+        "internal/stacktrace_win32-inl.inc",
+        "internal/stacktrace_x86-inl.inc",
+        "stacktrace.cc",
+    ],
+    hdrs = ["stacktrace.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":debugging_internal",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+    ],
+)
+
+cc_library(
+    name = "symbolize",
+    srcs = [
+        "symbolize.cc",
+        "symbolize_elf.inc",
+        "symbolize_unimplemented.inc",
+        "symbolize_win32.inc",
+    ],
+    hdrs = [
+        "internal/symbolize.h",
+        "symbolize.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS + select({
+        "//absl:windows": ["-DEFAULTLIB:dbghelp.lib"],
+        "//conditions:default": [],
+    }),
+    deps = [
+        ":debugging_internal",
+        ":demangle_internal",
+        "//absl/base",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:dynamic_annotations",
+        "//absl/base:malloc_internal",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_test(
+    name = "symbolize_test",
+    srcs = ["symbolize_test.cc"],
+    copts = ABSL_TEST_COPTS + select({
+        "//absl:windows": ["/Z7"],
+        "//conditions:default": [],
+    }),
+    linkopts = ABSL_DEFAULT_LINKOPTS + select({
+        "//absl:windows": ["/DEBUG"],
+        "//conditions:default": [],
+    }),
+    deps = [
+        ":stack_consumption",
+        ":symbolize",
+        "//absl/base",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+        "//absl/memory",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_library(
+    name = "examine_stack",
+    srcs = [
+        "internal/examine_stack.cc",
+    ],
+    hdrs = [
+        "internal/examine_stack.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":stacktrace",
+        ":symbolize",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_library(
+    name = "failure_signal_handler",
+    srcs = ["failure_signal_handler.cc"],
+    hdrs = ["failure_signal_handler.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":examine_stack",
+        ":stacktrace",
+        "//absl/base",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:errno_saver",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_test(
+    name = "failure_signal_handler_test",
+    srcs = ["failure_signal_handler_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = select({
+        "//absl:windows": [],
+        "//conditions:default": ["-pthread"],
+    }) + ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":failure_signal_handler",
+        ":stacktrace",
+        ":symbolize",
+        "//absl/base:raw_logging_internal",
+        "//absl/strings",
+        "@com_google_googletest//:gtest",
+    ],
+)
+
+cc_library(
+    name = "debugging_internal",
+    srcs = [
+        "internal/address_is_readable.cc",
+        "internal/elf_mem_image.cc",
+        "internal/vdso_support.cc",
+    ],
+    hdrs = [
+        "internal/address_is_readable.h",
+        "internal/elf_mem_image.h",
+        "internal/vdso_support.h",
+    ],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:dynamic_annotations",
+        "//absl/base:errno_saver",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_library(
+    name = "demangle_internal",
+    srcs = ["internal/demangle.cc"],
+    hdrs = ["internal/demangle.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        "//absl/base",
+        "//absl/base:config",
+        "//absl/base:core_headers",
+    ],
+)
+
+cc_test(
+    name = "demangle_test",
+    srcs = ["internal/demangle_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":demangle_internal",
+        ":stack_consumption",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+        "//absl/memory",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "leak_check",
+    srcs = ["leak_check.cc"],
+    hdrs = ["leak_check.h"],
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        "//absl/base:config",
+        "//absl/base:core_headers",
+    ],
+)
+
+# Adding a dependency to leak_check_disable will disable
+# sanitizer leak checking (asan/lsan) in a test without
+# the need to mess around with build features.
+cc_library(
+    name = "leak_check_disable",
+    srcs = ["leak_check_disable.cc"],
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    linkstatic = 1,
+    deps = ["//absl/base:config"],
+    alwayslink = 1,
+)
+
+# These targets exists for use in tests only, explicitly configuring the
+# LEAK_SANITIZER macro. It must be linked with -fsanitize=leak for lsan.
+ABSL_LSAN_LINKOPTS = select({
+    "//absl:llvm_compiler": ["-fsanitize=leak"],
+    "//conditions:default": [],
+})
+
+cc_library(
+    name = "leak_check_api_enabled_for_testing",
+    testonly = 1,
+    srcs = ["leak_check.cc"],
+    hdrs = ["leak_check.h"],
+    copts = select({
+        "//absl:llvm_compiler": ["-DLEAK_SANITIZER"],
+        "//conditions:default": [],
+    }),
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        "//absl/base:config",
+    ],
+)
+
+cc_library(
+    name = "leak_check_api_disabled_for_testing",
+    testonly = 1,
+    srcs = ["leak_check.cc"],
+    hdrs = ["leak_check.h"],
+    copts = ["-ULEAK_SANITIZER"],
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        "//absl/base:config",
+    ],
+)
+
+cc_test(
+    name = "leak_check_test",
+    srcs = ["leak_check_test.cc"],
+    copts = select({
+        "//absl:llvm_compiler": ["-DABSL_EXPECT_LEAK_SANITIZER"],
+        "//conditions:default": [],
+    }),
+    linkopts = ABSL_LSAN_LINKOPTS + ABSL_DEFAULT_LINKOPTS,
+    tags = ["notsan"],
+    deps = [
+        ":leak_check_api_enabled_for_testing",
+        "//absl/base",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_test(
+    name = "leak_check_no_lsan_test",
+    srcs = ["leak_check_test.cc"],
+    copts = ["-UABSL_EXPECT_LEAK_SANITIZER"],
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    tags = ["noasan"],
+    deps = [
+        ":leak_check_api_disabled_for_testing",
+        "//absl/base",  # for raw_logging
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+# Test that leak checking is skipped when lsan is enabled but
+# ":leak_check_disable" is linked in.
+#
+# This test should fail in the absence of a dependency on ":leak_check_disable"
+cc_test(
+    name = "disabled_leak_check_test",
+    srcs = ["leak_check_fail_test.cc"],
+    linkopts = ABSL_LSAN_LINKOPTS + ABSL_DEFAULT_LINKOPTS,
+    tags = ["notsan"],
+    deps = [
+        ":leak_check_api_enabled_for_testing",
+        ":leak_check_disable",
+        "//absl/base",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
+cc_library(
+    name = "stack_consumption",
+    testonly = 1,
+    srcs = ["internal/stack_consumption.cc"],
+    hdrs = ["internal/stack_consumption.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        "//absl/base:config",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+    ],
+)
+
+cc_test(
+    name = "stack_consumption_test",
+    srcs = ["internal/stack_consumption_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    linkopts = ABSL_DEFAULT_LINKOPTS,
+    deps = [
+        ":stack_consumption",
+        "//absl/base:core_headers",
+        "//absl/base:raw_logging_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
diff --git a/third_party/abseil_cpp/absl/debugging/CMakeLists.txt b/third_party/abseil_cpp/absl/debugging/CMakeLists.txt
new file mode 100644
index 000000000000..77336159393d
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/CMakeLists.txt
@@ -0,0 +1,333 @@
+#
+# Copyright 2017 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+absl_cc_library(
+  NAME
+    stacktrace
+  HDRS
+    "stacktrace.h"
+    "internal/stacktrace_aarch64-inl.inc"
+    "internal/stacktrace_arm-inl.inc"
+    "internal/stacktrace_config.h"
+    "internal/stacktrace_generic-inl.inc"
+    "internal/stacktrace_powerpc-inl.inc"
+    "internal/stacktrace_unimplemented-inl.inc"
+    "internal/stacktrace_win32-inl.inc"
+    "internal/stacktrace_x86-inl.inc"
+  SRCS
+    "stacktrace.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::debugging_internal
+    absl::config
+    absl::core_headers
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    symbolize
+  HDRS
+    "symbolize.h"
+    "internal/symbolize.h"
+  SRCS
+    "symbolize.cc"
+    "symbolize_elf.inc"
+    "symbolize_unimplemented.inc"
+    "symbolize_win32.inc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  LINKOPTS
+    ${ABSL_DEFAULT_LINKOPTS}
+    $<$<BOOL:${MINGW}>:"dbghelp">
+  DEPS
+    absl::debugging_internal
+    absl::demangle_internal
+    absl::base
+    absl::config
+    absl::core_headers
+    absl::dynamic_annotations
+    absl::malloc_internal
+    absl::raw_logging_internal
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    symbolize_test
+  SRCS
+    "symbolize_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+    $<$<BOOL:${MSVC}>:-Z7>
+  LINKOPTS
+    $<$<BOOL:${MSVC}>:-DEBUG>
+  DEPS
+    absl::stack_consumption
+    absl::symbolize
+    absl::base
+    absl::core_headers
+    absl::memory
+    absl::raw_logging_internal
+    gmock
+)
+
+absl_cc_library(
+  NAME
+    examine_stack
+  HDRS
+    "internal/examine_stack.h"
+  SRCS
+    "internal/examine_stack.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::stacktrace
+    absl::symbolize
+    absl::config
+    absl::core_headers
+    absl::raw_logging_internal
+)
+
+absl_cc_library(
+  NAME
+    failure_signal_handler
+  HDRS
+    "failure_signal_handler.h"
+  SRCS
+    "failure_signal_handler.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::examine_stack
+    absl::stacktrace
+    absl::base
+    absl::config
+    absl::core_headers
+    absl::errno_saver
+    absl::raw_logging_internal
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    failure_signal_handler_test
+  SRCS
+    "failure_signal_handler_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::failure_signal_handler
+    absl::stacktrace
+    absl::symbolize
+    absl::strings
+    absl::raw_logging_internal
+    Threads::Threads
+    gmock
+)
+
+absl_cc_library(
+  NAME
+    debugging_internal
+  HDRS
+    "internal/address_is_readable.h"
+    "internal/elf_mem_image.h"
+    "internal/vdso_support.h"
+  SRCS
+    "internal/address_is_readable.cc"
+    "internal/elf_mem_image.cc"
+    "internal/vdso_support.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::core_headers
+    absl::config
+    absl::dynamic_annotations
+    absl::errno_saver
+    absl::raw_logging_internal
+)
+
+absl_cc_library(
+  NAME
+    demangle_internal
+  HDRS
+    "internal/demangle.h"
+  SRCS
+    "internal/demangle.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::base
+    absl::core_headers
+  PUBLIC
+)
+
+absl_cc_test(
+  NAME
+    demangle_test
+  SRCS
+    "internal/demangle_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::demangle_internal
+    absl::stack_consumption
+    absl::core_headers
+    absl::memory
+    absl::raw_logging_internal
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    leak_check
+  HDRS
+    "leak_check.h"
+  SRCS
+    "leak_check.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::config
+    absl::core_headers
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    leak_check_disable
+  SRCS
+    "leak_check_disable.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  PUBLIC
+)
+
+absl_cc_library(
+  NAME
+    leak_check_api_enabled_for_testing
+  HDRS
+    "leak_check.h"
+  SRCS
+    "leak_check.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+    $<$<BOOL:${ABSL_HAVE_LSAN}>:-DLEAK_SANITIZER>
+  TESTONLY
+)
+
+absl_cc_library(
+  NAME
+    leak_check_api_disabled_for_testing
+  HDRS
+    "leak_check.h"
+  SRCS
+    "leak_check.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+    "-ULEAK_SANITIZER"
+  TESTONLY
+)
+
+absl_cc_test(
+  NAME
+    leak_check_test
+  SRCS
+    "leak_check_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+    "$<$<BOOL:${ABSL_HAVE_LSAN}>:-DABSL_EXPECT_LEAK_SANITIZER>"
+  LINKOPTS
+    "${ABSL_LSAN_LINKOPTS}"
+  DEPS
+    absl::leak_check_api_enabled_for_testing
+    absl::base
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    leak_check_no_lsan_test
+  SRCS
+    "leak_check_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+    "-UABSL_EXPECT_LEAK_SANITIZER"
+  DEPS
+    absl::leak_check_api_disabled_for_testing
+    absl::base
+    gmock_main
+)
+
+absl_cc_test(
+  NAME
+    disabled_leak_check_test
+  SRCS
+    "leak_check_fail_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  LINKOPTS
+    "${ABSL_LSAN_LINKOPTS}"
+  DEPS
+    absl::leak_check_api_enabled_for_testing
+    absl::leak_check_disable
+    absl::base
+    absl::raw_logging_internal
+    gmock_main
+)
+
+absl_cc_library(
+  NAME
+    stack_consumption
+  HDRS
+    "internal/stack_consumption.h"
+  SRCS
+    "internal/stack_consumption.cc"
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::config
+    absl::core_headers
+    absl::raw_logging_internal
+  TESTONLY
+)
+
+absl_cc_test(
+  NAME
+    stack_consumption_test
+  SRCS
+    "internal/stack_consumption_test.cc"
+  COPTS
+    ${ABSL_TEST_COPTS}
+  DEPS
+    absl::stack_consumption
+    absl::core_headers
+    absl::raw_logging_internal
+    gmock_main
+)
+
+# component target
+absl_cc_library(
+  NAME
+    debugging
+  COPTS
+    ${ABSL_DEFAULT_COPTS}
+  DEPS
+    absl::stacktrace
+    absl::leak_check
+  PUBLIC
+)
diff --git a/third_party/abseil_cpp/absl/debugging/failure_signal_handler.cc b/third_party/abseil_cpp/absl/debugging/failure_signal_handler.cc
new file mode 100644
index 000000000000..1f69bfa84dd9
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/failure_signal_handler.cc
@@ -0,0 +1,370 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "absl/debugging/failure_signal_handler.h"
+
+#include "absl/base/config.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
+#ifdef __APPLE__
+#include <TargetConditionals.h>
+#endif
+
+#ifdef ABSL_HAVE_MMAP
+#include <sys/mman.h>
+#endif
+
+#include <algorithm>
+#include <atomic>
+#include <cerrno>
+#include <csignal>
+#include <cstdio>
+#include <cstring>
+#include <ctime>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/errno_saver.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/sysinfo.h"
+#include "absl/debugging/internal/examine_stack.h"
+#include "absl/debugging/stacktrace.h"
+
+#ifndef _WIN32
+#define ABSL_HAVE_SIGACTION
+// Apple WatchOS and TVOS don't allow sigaltstack
+#if !(defined(TARGET_OS_WATCH) && TARGET_OS_WATCH) && \
+    !(defined(TARGET_OS_TV) && TARGET_OS_TV)
+#define ABSL_HAVE_SIGALTSTACK
+#endif
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+ABSL_CONST_INIT static FailureSignalHandlerOptions fsh_options;
+
+// Resets the signal handler for signo to the default action for that
+// signal, then raises the signal.
+static void RaiseToDefaultHandler(int signo) {
+  signal(signo, SIG_DFL);
+  raise(signo);
+}
+
+struct FailureSignalData {
+  const int signo;
+  const char* const as_string;
+#ifdef ABSL_HAVE_SIGACTION
+  struct sigaction previous_action;
+  // StructSigaction is used to silence -Wmissing-field-initializers.
+  using StructSigaction = struct sigaction;
+  #define FSD_PREVIOUS_INIT FailureSignalData::StructSigaction()
+#else
+  void (*previous_handler)(int);
+  #define FSD_PREVIOUS_INIT SIG_DFL
+#endif
+};
+
+ABSL_CONST_INIT static FailureSignalData failure_signal_data[] = {
+    {SIGSEGV, "SIGSEGV", FSD_PREVIOUS_INIT},
+    {SIGILL, "SIGILL", FSD_PREVIOUS_INIT},
+    {SIGFPE, "SIGFPE", FSD_PREVIOUS_INIT},
+    {SIGABRT, "SIGABRT", FSD_PREVIOUS_INIT},
+    {SIGTERM, "SIGTERM", FSD_PREVIOUS_INIT},
+#ifndef _WIN32
+    {SIGBUS, "SIGBUS", FSD_PREVIOUS_INIT},
+    {SIGTRAP, "SIGTRAP", FSD_PREVIOUS_INIT},
+#endif
+};
+
+#undef FSD_PREVIOUS_INIT
+
+static void RaiseToPreviousHandler(int signo) {
+  // Search for the previous handler.
+  for (const auto& it : failure_signal_data) {
+    if (it.signo == signo) {
+#ifdef ABSL_HAVE_SIGACTION
+      sigaction(signo, &it.previous_action, nullptr);
+#else
+      signal(signo, it.previous_handler);
+#endif
+      raise(signo);
+      return;
+    }
+  }
+
+  // Not found, use the default handler.
+  RaiseToDefaultHandler(signo);
+}
+
+namespace debugging_internal {
+
+const char* FailureSignalToString(int signo) {
+  for (const auto& it : failure_signal_data) {
+    if (it.signo == signo) {
+      return it.as_string;
+    }
+  }
+  return "";
+}
+
+}  // namespace debugging_internal
+
+#ifdef ABSL_HAVE_SIGALTSTACK
+
+static bool SetupAlternateStackOnce() {
+#if defined(__wasm__) || defined (__asjms__)
+  const size_t page_mask = getpagesize() - 1;
+#else
+  const size_t page_mask = sysconf(_SC_PAGESIZE) - 1;
+#endif
+  size_t stack_size = (std::max(SIGSTKSZ, 65536) + page_mask) & ~page_mask;
+#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
+    defined(THREAD_SANITIZER)
+  // Account for sanitizer instrumentation requiring additional stack space.
+  stack_size *= 5;
+#endif
+
+  stack_t sigstk;
+  memset(&sigstk, 0, sizeof(sigstk));
+  sigstk.ss_size = stack_size;
+
+#ifdef ABSL_HAVE_MMAP
+#ifndef MAP_STACK
+#define MAP_STACK 0
+#endif
+#if defined(MAP_ANON) && !defined(MAP_ANONYMOUS)
+#define MAP_ANONYMOUS MAP_ANON
+#endif
+  sigstk.ss_sp = mmap(nullptr, sigstk.ss_size, PROT_READ | PROT_WRITE,
+                      MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+  if (sigstk.ss_sp == MAP_FAILED) {
+    ABSL_RAW_LOG(FATAL, "mmap() for alternate signal stack failed");
+  }
+#else
+  sigstk.ss_sp = malloc(sigstk.ss_size);
+  if (sigstk.ss_sp == nullptr) {
+    ABSL_RAW_LOG(FATAL, "malloc() for alternate signal stack failed");
+  }
+#endif
+
+  if (sigaltstack(&sigstk, nullptr) != 0) {
+    ABSL_RAW_LOG(FATAL, "sigaltstack() failed with errno=%d", errno);
+  }
+  return true;
+}
+
+#endif
+
+#ifdef ABSL_HAVE_SIGACTION
+
+// Sets up an alternate stack for signal handlers once.
+// Returns the appropriate flag for sig_action.sa_flags
+// if the system supports using an alternate stack.
+static int MaybeSetupAlternateStack() {
+#ifdef ABSL_HAVE_SIGALTSTACK
+  ABSL_ATTRIBUTE_UNUSED static const bool kOnce = SetupAlternateStackOnce();
+  return SA_ONSTACK;
+#else
+  return 0;
+#endif
+}
+
+static void InstallOneFailureHandler(FailureSignalData* data,
+                                     void (*handler)(int, siginfo_t*, void*)) {
+  struct sigaction act;
+  memset(&act, 0, sizeof(act));
+  sigemptyset(&act.sa_mask);
+  act.sa_flags |= SA_SIGINFO;
+  // SA_NODEFER is required to handle SIGABRT from
+  // ImmediateAbortSignalHandler().
+  act.sa_flags |= SA_NODEFER;
+  if (fsh_options.use_alternate_stack) {
+    act.sa_flags |= MaybeSetupAlternateStack();
+  }
+  act.sa_sigaction = handler;
+  ABSL_RAW_CHECK(sigaction(data->signo, &act, &data->previous_action) == 0,
+                 "sigaction() failed");
+}
+
+#else
+
+static void InstallOneFailureHandler(FailureSignalData* data,
+                                     void (*handler)(int)) {
+  data->previous_handler = signal(data->signo, handler);
+  ABSL_RAW_CHECK(data->previous_handler != SIG_ERR, "signal() failed");
+}
+
+#endif
+
+static void WriteToStderr(const char* data) {
+  absl::base_internal::ErrnoSaver errno_saver;
+  absl::raw_logging_internal::SafeWriteToStderr(data, strlen(data));
+}
+
+static void WriteSignalMessage(int signo, void (*writerfn)(const char*)) {
+  char buf[64];
+  const char* const signal_string =
+      debugging_internal::FailureSignalToString(signo);
+  if (signal_string != nullptr && signal_string[0] != '\0') {
+    snprintf(buf, sizeof(buf), "*** %s received at time=%ld ***\n",
+             signal_string,
+             static_cast<long>(time(nullptr)));  // NOLINT(runtime/int)
+  } else {
+    snprintf(buf, sizeof(buf), "*** Signal %d received at time=%ld ***\n",
+             signo, static_cast<long>(time(nullptr)));  // NOLINT(runtime/int)
+  }
+  writerfn(buf);
+}
+
+// `void*` might not be big enough to store `void(*)(const char*)`.
+struct WriterFnStruct {
+  void (*writerfn)(const char*);
+};
+
+// Many of the absl::debugging_internal::Dump* functions in
+// examine_stack.h take a writer function pointer that has a void* arg
+// for historical reasons. failure_signal_handler_writer only takes a
+// data pointer. This function converts between these types.
+static void WriterFnWrapper(const char* data, void* arg) {
+  static_cast<WriterFnStruct*>(arg)->writerfn(data);
+}
+
+// Convenient wrapper around DumpPCAndFrameSizesAndStackTrace() for signal
+// handlers. "noinline" so that GetStackFrames() skips the top-most stack
+// frame for this function.
+ABSL_ATTRIBUTE_NOINLINE static void WriteStackTrace(
+    void* ucontext, bool symbolize_stacktrace,
+    void (*writerfn)(const char*, void*), void* writerfn_arg) {
+  constexpr int kNumStackFrames = 32;
+  void* stack[kNumStackFrames];
+  int frame_sizes[kNumStackFrames];
+  int min_dropped_frames;
+  int depth = absl::GetStackFramesWithContext(
+      stack, frame_sizes, kNumStackFrames,
+      1,  // Do not include this function in stack trace.
+      ucontext, &min_dropped_frames);
+  absl::debugging_internal::DumpPCAndFrameSizesAndStackTrace(
+      absl::debugging_internal::GetProgramCounter(ucontext), stack, frame_sizes,
+      depth, min_dropped_frames, symbolize_stacktrace, writerfn, writerfn_arg);
+}
+
+// Called by AbslFailureSignalHandler() to write the failure info. It is
+// called once with writerfn set to WriteToStderr() and then possibly
+// with writerfn set to the user provided function.
+static void WriteFailureInfo(int signo, void* ucontext,
+                             void (*writerfn)(const char*)) {
+  WriterFnStruct writerfn_struct{writerfn};
+  WriteSignalMessage(signo, writerfn);
+  WriteStackTrace(ucontext, fsh_options.symbolize_stacktrace, WriterFnWrapper,
+                  &writerfn_struct);
+}
+
+// absl::SleepFor() can't be used here since AbslInternalSleepFor()
+// may be overridden to do something that isn't async-signal-safe on
+// some platforms.
+static void PortableSleepForSeconds(int seconds) {
+#ifdef _WIN32
+  Sleep(seconds * 1000);
+#else
+  struct timespec sleep_time;
+  sleep_time.tv_sec = seconds;
+  sleep_time.tv_nsec = 0;
+  while (nanosleep(&sleep_time, &sleep_time) != 0 && errno == EINTR) {}
+#endif
+}
+
+#ifdef ABSL_HAVE_ALARM
+// AbslFailureSignalHandler() installs this as a signal handler for
+// SIGALRM, then sets an alarm to be delivered to the program after a
+// set amount of time. If AbslFailureSignalHandler() hangs for more than
+// the alarm timeout, ImmediateAbortSignalHandler() will abort the
+// program.
+static void ImmediateAbortSignalHandler(int) {
+  RaiseToDefaultHandler(SIGABRT);
+}
+#endif
+
+// absl::base_internal::GetTID() returns pid_t on most platforms, but
+// returns absl::base_internal::pid_t on Windows.
+using GetTidType = decltype(absl::base_internal::GetTID());
+ABSL_CONST_INIT static std::atomic<GetTidType> failed_tid(0);
+
+#ifndef ABSL_HAVE_SIGACTION
+static void AbslFailureSignalHandler(int signo) {
+  void* ucontext = nullptr;
+#else
+static void AbslFailureSignalHandler(int signo, siginfo_t*, void* ucontext) {
+#endif
+
+  const GetTidType this_tid = absl::base_internal::GetTID();
+  GetTidType previous_failed_tid = 0;
+  if (!failed_tid.compare_exchange_strong(
+          previous_failed_tid, static_cast<intptr_t>(this_tid),
+          std::memory_order_acq_rel, std::memory_order_relaxed)) {
+    ABSL_RAW_LOG(
+        ERROR,
+        "Signal %d raised at PC=%p while already in AbslFailureSignalHandler()",
+        signo, absl::debugging_internal::GetProgramCounter(ucontext));
+    if (this_tid != previous_failed_tid) {
+      // Another thread is already in AbslFailureSignalHandler(), so wait
+      // a bit for it to finish. If the other thread doesn't kill us,
+      // we do so after sleeping.
+      PortableSleepForSeconds(3);
+      RaiseToDefaultHandler(signo);
+      // The recursively raised signal may be blocked until we return.
+      return;
+    }
+  }
+
+#ifdef ABSL_HAVE_ALARM
+  // Set an alarm to abort the program in case this code hangs or deadlocks.
+  if (fsh_options.alarm_on_failure_secs > 0) {
+    alarm(0);  // Cancel any existing alarms.
+    signal(SIGALRM, ImmediateAbortSignalHandler);
+    alarm(fsh_options.alarm_on_failure_secs);
+  }
+#endif
+
+  // First write to stderr.
+  WriteFailureInfo(signo, ucontext, WriteToStderr);
+
+  // Riskier code (because it is less likely to be async-signal-safe)
+  // goes after this point.
+  if (fsh_options.writerfn != nullptr) {
+    WriteFailureInfo(signo, ucontext, fsh_options.writerfn);
+  }
+
+  if (fsh_options.call_previous_handler) {
+    RaiseToPreviousHandler(signo);
+  } else {
+    RaiseToDefaultHandler(signo);
+  }
+}
+
+void InstallFailureSignalHandler(const FailureSignalHandlerOptions& options) {
+  fsh_options = options;
+  for (auto& it : failure_signal_data) {
+    InstallOneFailureHandler(&it, AbslFailureSignalHandler);
+  }
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/failure_signal_handler.h b/third_party/abseil_cpp/absl/debugging/failure_signal_handler.h
new file mode 100644
index 000000000000..0c0f585d0fb4
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/failure_signal_handler.h
@@ -0,0 +1,121 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: failure_signal_handler.h
+// -----------------------------------------------------------------------------
+//
+// This file configures the Abseil *failure signal handler* to capture and dump
+// useful debugging information (such as a stacktrace) upon program failure.
+//
+// To use the failure signal handler, call `absl::InstallFailureSignalHandler()`
+// very early in your program, usually in the first few lines of main():
+//
+// int main(int argc, char** argv) {
+//   // Initialize the symbolizer to get a human-readable stack trace
+//   absl::InitializeSymbolizer(argv[0]);
+//
+//   absl::FailureSignalHandlerOptions options;
+//   absl::InstallFailureSignalHandler(options);
+//   DoSomethingInteresting();
+//   return 0;
+// }
+//
+// Any program that raises a fatal signal (such as `SIGSEGV`, `SIGILL`,
+// `SIGFPE`, `SIGABRT`, `SIGTERM`, `SIGBUG`, and `SIGTRAP`) will call the
+// installed failure signal handler and provide debugging information to stderr.
+//
+// Note that you should *not* install the Abseil failure signal handler more
+// than once. You may, of course, have another (non-Abseil) failure signal
+// handler installed (which would be triggered if Abseil's failure signal
+// handler sets `call_previous_handler` to `true`).
+
+#ifndef ABSL_DEBUGGING_FAILURE_SIGNAL_HANDLER_H_
+#define ABSL_DEBUGGING_FAILURE_SIGNAL_HANDLER_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// FailureSignalHandlerOptions
+//
+// Struct for holding `absl::InstallFailureSignalHandler()` configuration
+// options.
+struct FailureSignalHandlerOptions {
+  // If true, try to symbolize the stacktrace emitted on failure, provided that
+  // you have initialized a symbolizer for that purpose. (See symbolize.h for
+  // more information.)
+  bool symbolize_stacktrace = true;
+
+  // If true, try to run signal handlers on an alternate stack (if supported on
+  // the given platform). An alternate stack is useful for program crashes due
+  // to a stack overflow; by running on a alternate stack, the signal handler
+  // may run even when normal stack space has been exausted. The downside of
+  // using an alternate stack is that extra memory for the alternate stack needs
+  // to be pre-allocated.
+  bool use_alternate_stack = true;
+
+  // If positive, indicates the number of seconds after which the failure signal
+  // handler is invoked to abort the program. Setting such an alarm is useful in
+  // cases where the failure signal handler itself may become hung or
+  // deadlocked.
+  int alarm_on_failure_secs = 3;
+
+  // If true, call the previously registered signal handler for the signal that
+  // was received (if one was registered) after the existing signal handler
+  // runs. This mechanism can be used to chain signal handlers together.
+  //
+  // If false, the signal is raised to the default handler for that signal
+  // (which normally terminates the program).
+  //
+  // IMPORTANT: If true, the chained fatal signal handlers must not try to
+  // recover from the fatal signal. Instead, they should terminate the program
+  // via some mechanism, like raising the default handler for the signal, or by
+  // calling `_exit()`. Note that the failure signal handler may put parts of
+  // the Abseil library into a state from which they cannot recover.
+  bool call_previous_handler = false;
+
+  // If non-null, indicates a pointer to a callback function that will be called
+  // upon failure, with a string argument containing failure data. This function
+  // may be used as a hook to write failure data to a secondary location, such
+  // as a log file. This function may also be called with null data, as a hint
+  // to flush any buffered data before the program may be terminated. Consider
+  // flushing any buffered data in all calls to this function.
+  //
+  // Since this function runs within a signal handler, it should be
+  // async-signal-safe if possible.
+  // See http://man7.org/linux/man-pages/man7/signal-safety.7.html
+  void (*writerfn)(const char*) = nullptr;
+};
+
+// InstallFailureSignalHandler()
+//
+// Installs a signal handler for the common failure signals `SIGSEGV`, `SIGILL`,
+// `SIGFPE`, `SIGABRT`, `SIGTERM`, `SIGBUG`, and `SIGTRAP` (provided they exist
+// on the given platform). The failure signal handler dumps program failure data
+// useful for debugging in an unspecified format to stderr. This data may
+// include the program counter, a stacktrace, and register information on some
+// systems; do not rely on an exact format for the output, as it is subject to
+// change.
+void InstallFailureSignalHandler(const FailureSignalHandlerOptions& options);
+
+namespace debugging_internal {
+const char* FailureSignalToString(int signo);
+}  // namespace debugging_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_FAILURE_SIGNAL_HANDLER_H_
diff --git a/third_party/abseil_cpp/absl/debugging/failure_signal_handler_test.cc b/third_party/abseil_cpp/absl/debugging/failure_signal_handler_test.cc
new file mode 100644
index 000000000000..d8283b2f47cd
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/failure_signal_handler_test.cc
@@ -0,0 +1,159 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "absl/debugging/failure_signal_handler.h"
+
+#include <csignal>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <fstream>
+
+#include "gtest/gtest.h"
+#include "gmock/gmock.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/debugging/stacktrace.h"
+#include "absl/debugging/symbolize.h"
+#include "absl/strings/match.h"
+#include "absl/strings/str_cat.h"
+
+namespace {
+
+using testing::StartsWith;
+
+#if GTEST_HAS_DEATH_TEST
+
+// For the parameterized death tests. GetParam() returns the signal number.
+using FailureSignalHandlerDeathTest = ::testing::TestWithParam<int>;
+
+// This function runs in a fork()ed process on most systems.
+void InstallHandlerAndRaise(int signo) {
+  absl::InstallFailureSignalHandler(absl::FailureSignalHandlerOptions());
+  raise(signo);
+}
+
+TEST_P(FailureSignalHandlerDeathTest, AbslFailureSignal) {
+  const int signo = GetParam();
+  std::string exit_regex = absl::StrCat(
+      "\\*\\*\\* ", absl::debugging_internal::FailureSignalToString(signo),
+      " received at time=");
+#ifndef _WIN32
+  EXPECT_EXIT(InstallHandlerAndRaise(signo), testing::KilledBySignal(signo),
+              exit_regex);
+#else
+  // Windows doesn't have testing::KilledBySignal().
+  EXPECT_DEATH_IF_SUPPORTED(InstallHandlerAndRaise(signo), exit_regex);
+#endif
+}
+
+ABSL_CONST_INIT FILE* error_file = nullptr;
+
+void WriteToErrorFile(const char* msg) {
+  if (msg != nullptr) {
+    ABSL_RAW_CHECK(fwrite(msg, strlen(msg), 1, error_file) == 1,
+                   "fwrite() failed");
+  }
+  ABSL_RAW_CHECK(fflush(error_file) == 0, "fflush() failed");
+}
+
+std::string GetTmpDir() {
+  // TEST_TMPDIR is set by Bazel. Try the others when not running under Bazel.
+  static const char* const kTmpEnvVars[] = {"TEST_TMPDIR", "TMPDIR", "TEMP",
+                                            "TEMPDIR", "TMP"};
+  for (const char* const var : kTmpEnvVars) {
+    const char* tmp_dir = std::getenv(var);
+    if (tmp_dir != nullptr) {
+      return tmp_dir;
+    }
+  }
+
+  // Try something reasonable.
+  return "/tmp";
+}
+
+// This function runs in a fork()ed process on most systems.
+void InstallHandlerWithWriteToFileAndRaise(const char* file, int signo) {
+  error_file = fopen(file, "w");
+  ABSL_RAW_CHECK(error_file != nullptr, "Failed create error_file");
+  absl::FailureSignalHandlerOptions options;
+  options.writerfn = WriteToErrorFile;
+  absl::InstallFailureSignalHandler(options);
+  raise(signo);
+}
+
+TEST_P(FailureSignalHandlerDeathTest, AbslFatalSignalsWithWriterFn) {
+  const int signo = GetParam();
+  std::string tmp_dir = GetTmpDir();
+  std::string file = absl::StrCat(tmp_dir, "/signo_", signo);
+
+  std::string exit_regex = absl::StrCat(
+      "\\*\\*\\* ", absl::debugging_internal::FailureSignalToString(signo),
+      " received at time=");
+#ifndef _WIN32
+  EXPECT_EXIT(InstallHandlerWithWriteToFileAndRaise(file.c_str(), signo),
+              testing::KilledBySignal(signo), exit_regex);
+#else
+  // Windows doesn't have testing::KilledBySignal().
+  EXPECT_DEATH_IF_SUPPORTED(
+      InstallHandlerWithWriteToFileAndRaise(file.c_str(), signo), exit_regex);
+#endif
+
+  // Open the file in this process and check its contents.
+  std::fstream error_output(file);
+  ASSERT_TRUE(error_output.is_open()) << file;
+  std::string error_line;
+  std::getline(error_output, error_line);
+  EXPECT_THAT(
+      error_line,
+      StartsWith(absl::StrCat(
+          "*** ", absl::debugging_internal::FailureSignalToString(signo),
+          " received at ")));
+
+  if (absl::debugging_internal::StackTraceWorksForTest()) {
+    std::getline(error_output, error_line);
+    EXPECT_THAT(error_line, StartsWith("PC: "));
+  }
+}
+
+constexpr int kFailureSignals[] = {
+    SIGSEGV, SIGILL,  SIGFPE, SIGABRT, SIGTERM,
+#ifndef _WIN32
+    SIGBUS,  SIGTRAP,
+#endif
+};
+
+std::string SignalParamToString(const ::testing::TestParamInfo<int>& info) {
+  std::string result =
+      absl::debugging_internal::FailureSignalToString(info.param);
+  if (result.empty()) {
+    result = absl::StrCat(info.param);
+  }
+  return result;
+}
+
+INSTANTIATE_TEST_SUITE_P(AbslDeathTest, FailureSignalHandlerDeathTest,
+                         ::testing::ValuesIn(kFailureSignals),
+                         SignalParamToString);
+
+#endif  // GTEST_HAS_DEATH_TEST
+
+}  // namespace
+
+int main(int argc, char** argv) {
+  absl::InitializeSymbolizer(argv[0]);
+  testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}
diff --git a/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc b/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc
new file mode 100644
index 000000000000..65376063669f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc
@@ -0,0 +1,138 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// base::AddressIsReadable() probes an address to see whether it is readable,
+// without faulting.
+
+#include "absl/debugging/internal/address_is_readable.h"
+
+#if !defined(__linux__) || defined(__ANDROID__)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// On platforms other than Linux, just return true.
+bool AddressIsReadable(const void* /* addr */) { return true; }
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else
+
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include <atomic>
+#include <cerrno>
+#include <cstdint>
+
+#include "absl/base/internal/errno_saver.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Pack a pid and two file descriptors into a 64-bit word,
+// using 16, 24, and 24 bits for each respectively.
+static uint64_t Pack(uint64_t pid, uint64_t read_fd, uint64_t write_fd) {
+  ABSL_RAW_CHECK((read_fd >> 24) == 0 && (write_fd >> 24) == 0,
+                 "fd out of range");
+  return (pid << 48) | ((read_fd & 0xffffff) << 24) | (write_fd & 0xffffff);
+}
+
+// Unpack x into a pid and two file descriptors, where x was created with
+// Pack().
+static void Unpack(uint64_t x, int *pid, int *read_fd, int *write_fd) {
+  *pid = x >> 48;
+  *read_fd = (x >> 24) & 0xffffff;
+  *write_fd = x & 0xffffff;
+}
+
+// Return whether the byte at *addr is readable, without faulting.
+// Save and restores errno.   Returns true on systems where
+// unimplemented.
+// This is a namespace-scoped variable for correct zero-initialization.
+static std::atomic<uint64_t> pid_and_fds;  // initially 0, an invalid pid.
+bool AddressIsReadable(const void *addr) {
+  absl::base_internal::ErrnoSaver errno_saver;
+  // We test whether a byte is readable by using write().  Normally, this would
+  // be done via a cached file descriptor to /dev/null, but linux fails to
+  // check whether the byte is readable when the destination is /dev/null, so
+  // we use a cached pipe.  We store the pid of the process that created the
+  // pipe to handle the case where a process forks, and the child closes all
+  // the file descriptors and then calls this routine.  This is not perfect:
+  // the child could use the routine, then close all file descriptors and then
+  // use this routine again.  But the likely use of this routine is when
+  // crashing, to test the validity of pages when dumping the stack.  Beware
+  // that we may leak file descriptors, but we're unlikely to leak many.
+  int bytes_written;
+  int current_pid = getpid() & 0xffff;   // we use only the low order 16 bits
+  do {  // until we do not get EBADF trying to use file descriptors
+    int pid;
+    int read_fd;
+    int write_fd;
+    uint64_t local_pid_and_fds = pid_and_fds.load(std::memory_order_relaxed);
+    Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
+    while (current_pid != pid) {
+      int p[2];
+      // new pipe
+      if (pipe(p) != 0) {
+        ABSL_RAW_LOG(FATAL, "Failed to create pipe, errno=%d", errno);
+      }
+      fcntl(p[0], F_SETFD, FD_CLOEXEC);
+      fcntl(p[1], F_SETFD, FD_CLOEXEC);
+      uint64_t new_pid_and_fds = Pack(current_pid, p[0], p[1]);
+      if (pid_and_fds.compare_exchange_strong(
+              local_pid_and_fds, new_pid_and_fds, std::memory_order_relaxed,
+              std::memory_order_relaxed)) {
+        local_pid_and_fds = new_pid_and_fds;  // fds exposed to other threads
+      } else {  // fds not exposed to other threads; we can close them.
+        close(p[0]);
+        close(p[1]);
+        local_pid_and_fds = pid_and_fds.load(std::memory_order_relaxed);
+      }
+      Unpack(local_pid_and_fds, &pid, &read_fd, &write_fd);
+    }
+    errno = 0;
+    // Use syscall(SYS_write, ...) instead of write() to prevent ASAN
+    // and other checkers from complaining about accesses to arbitrary
+    // memory.
+    do {
+      bytes_written = syscall(SYS_write, write_fd, addr, 1);
+    } while (bytes_written == -1 && errno == EINTR);
+    if (bytes_written == 1) {   // remove the byte from the pipe
+      char c;
+      while (read(read_fd, &c, 1) == -1 && errno == EINTR) {
+      }
+    }
+    if (errno == EBADF) {  // Descriptors invalid.
+      // If pid_and_fds contains the problematic file descriptors we just used,
+      // this call will forget them, and the loop will try again.
+      pid_and_fds.compare_exchange_strong(local_pid_and_fds, 0,
+                                          std::memory_order_relaxed,
+                                          std::memory_order_relaxed);
+    }
+  } while (errno == EBADF);
+  return bytes_written == 1;
+}
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif
diff --git a/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.h b/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.h
new file mode 100644
index 000000000000..4bbaf4d69bd8
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.h
@@ -0,0 +1,32 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_ADDRESS_IS_READABLE_H_
+#define ABSL_DEBUGGING_INTERNAL_ADDRESS_IS_READABLE_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Return whether the byte at *addr is readable, without faulting.
+// Save and restores errno.
+bool AddressIsReadable(const void *addr);
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_ADDRESS_IS_READABLE_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/demangle.cc b/third_party/abseil_cpp/absl/debugging/internal/demangle.cc
new file mode 100644
index 000000000000..fc262e50ae50
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/demangle.cc
@@ -0,0 +1,1895 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// For reference check out:
+// https://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangling
+//
+// Note that we only have partial C++11 support yet.
+
+#include "absl/debugging/internal/demangle.h"
+
+#include <cstdint>
+#include <cstdio>
+#include <limits>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+typedef struct {
+  const char *abbrev;
+  const char *real_name;
+  // Number of arguments in <expression> context, or 0 if disallowed.
+  int arity;
+} AbbrevPair;
+
+// List of operators from Itanium C++ ABI.
+static const AbbrevPair kOperatorList[] = {
+    // New has special syntax (not currently supported).
+    {"nw", "new", 0},
+    {"na", "new[]", 0},
+
+    // Works except that the 'gs' prefix is not supported.
+    {"dl", "delete", 1},
+    {"da", "delete[]", 1},
+
+    {"ps", "+", 1},  // "positive"
+    {"ng", "-", 1},  // "negative"
+    {"ad", "&", 1},  // "address-of"
+    {"de", "*", 1},  // "dereference"
+    {"co", "~", 1},
+
+    {"pl", "+", 2},
+    {"mi", "-", 2},
+    {"ml", "*", 2},
+    {"dv", "/", 2},
+    {"rm", "%", 2},
+    {"an", "&", 2},
+    {"or", "|", 2},
+    {"eo", "^", 2},
+    {"aS", "=", 2},
+    {"pL", "+=", 2},
+    {"mI", "-=", 2},
+    {"mL", "*=", 2},
+    {"dV", "/=", 2},
+    {"rM", "%=", 2},
+    {"aN", "&=", 2},
+    {"oR", "|=", 2},
+    {"eO", "^=", 2},
+    {"ls", "<<", 2},
+    {"rs", ">>", 2},
+    {"lS", "<<=", 2},
+    {"rS", ">>=", 2},
+    {"eq", "==", 2},
+    {"ne", "!=", 2},
+    {"lt", "<", 2},
+    {"gt", ">", 2},
+    {"le", "<=", 2},
+    {"ge", ">=", 2},
+    {"nt", "!", 1},
+    {"aa", "&&", 2},
+    {"oo", "||", 2},
+    {"pp", "++", 1},
+    {"mm", "--", 1},
+    {"cm", ",", 2},
+    {"pm", "->*", 2},
+    {"pt", "->", 0},  // Special syntax
+    {"cl", "()", 0},  // Special syntax
+    {"ix", "[]", 2},
+    {"qu", "?", 3},
+    {"st", "sizeof", 0},  // Special syntax
+    {"sz", "sizeof", 1},  // Not a real operator name, but used in expressions.
+    {nullptr, nullptr, 0},
+};
+
+// List of builtin types from Itanium C++ ABI.
+//
+// Invariant: only one- or two-character type abbreviations here.
+static const AbbrevPair kBuiltinTypeList[] = {
+    {"v", "void", 0},
+    {"w", "wchar_t", 0},
+    {"b", "bool", 0},
+    {"c", "char", 0},
+    {"a", "signed char", 0},
+    {"h", "unsigned char", 0},
+    {"s", "short", 0},
+    {"t", "unsigned short", 0},
+    {"i", "int", 0},
+    {"j", "unsigned int", 0},
+    {"l", "long", 0},
+    {"m", "unsigned long", 0},
+    {"x", "long long", 0},
+    {"y", "unsigned long long", 0},
+    {"n", "__int128", 0},
+    {"o", "unsigned __int128", 0},
+    {"f", "float", 0},
+    {"d", "double", 0},
+    {"e", "long double", 0},
+    {"g", "__float128", 0},
+    {"z", "ellipsis", 0},
+
+    {"De", "decimal128", 0},      // IEEE 754r decimal floating point (128 bits)
+    {"Dd", "decimal64", 0},       // IEEE 754r decimal floating point (64 bits)
+    {"Dc", "decltype(auto)", 0},
+    {"Da", "auto", 0},
+    {"Dn", "std::nullptr_t", 0},  // i.e., decltype(nullptr)
+    {"Df", "decimal32", 0},       // IEEE 754r decimal floating point (32 bits)
+    {"Di", "char32_t", 0},
+    {"Ds", "char16_t", 0},
+    {"Dh", "float16", 0},         // IEEE 754r half-precision float (16 bits)
+    {nullptr, nullptr, 0},
+};
+
+// List of substitutions Itanium C++ ABI.
+static const AbbrevPair kSubstitutionList[] = {
+    {"St", "", 0},
+    {"Sa", "allocator", 0},
+    {"Sb", "basic_string", 0},
+    // std::basic_string<char, std::char_traits<char>,std::allocator<char> >
+    {"Ss", "string", 0},
+    // std::basic_istream<char, std::char_traits<char> >
+    {"Si", "istream", 0},
+    // std::basic_ostream<char, std::char_traits<char> >
+    {"So", "ostream", 0},
+    // std::basic_iostream<char, std::char_traits<char> >
+    {"Sd", "iostream", 0},
+    {nullptr, nullptr, 0},
+};
+
+// State needed for demangling.  This struct is copied in almost every stack
+// frame, so every byte counts.
+typedef struct {
+  int mangled_idx;                   // Cursor of mangled name.
+  int out_cur_idx;                   // Cursor of output string.
+  int prev_name_idx;                 // For constructors/destructors.
+  signed int prev_name_length : 16;  // For constructors/destructors.
+  signed int nest_level : 15;        // For nested names.
+  unsigned int append : 1;           // Append flag.
+  // Note: for some reason MSVC can't pack "bool append : 1" into the same int
+  // with the above two fields, so we use an int instead.  Amusingly it can pack
+  // "signed bool" as expected, but relying on that to continue to be a legal
+  // type seems ill-advised (as it's illegal in at least clang).
+} ParseState;
+
+static_assert(sizeof(ParseState) == 4 * sizeof(int),
+              "unexpected size of ParseState");
+
+// One-off state for demangling that's not subject to backtracking -- either
+// constant data, data that's intentionally immune to backtracking (steps), or
+// data that would never be changed by backtracking anyway (recursion_depth).
+//
+// Only one copy of this exists for each call to Demangle, so the size of this
+// struct is nearly inconsequential.
+typedef struct {
+  const char *mangled_begin;  // Beginning of input string.
+  char *out;                  // Beginning of output string.
+  int out_end_idx;            // One past last allowed output character.
+  int recursion_depth;        // For stack exhaustion prevention.
+  int steps;               // Cap how much work we'll do, regardless of depth.
+  ParseState parse_state;  // Backtrackable state copied for most frames.
+} State;
+
+namespace {
+// Prevent deep recursion / stack exhaustion.
+// Also prevent unbounded handling of complex inputs.
+class ComplexityGuard {
+ public:
+  explicit ComplexityGuard(State *state) : state_(state) {
+    ++state->recursion_depth;
+    ++state->steps;
+  }
+  ~ComplexityGuard() { --state_->recursion_depth; }
+
+  // 256 levels of recursion seems like a reasonable upper limit on depth.
+  // 128 is not enough to demagle synthetic tests from demangle_unittest.txt:
+  // "_ZaaZZZZ..." and "_ZaaZcvZcvZ..."
+  static constexpr int kRecursionDepthLimit = 256;
+
+  // We're trying to pick a charitable upper-limit on how many parse steps are
+  // necessary to handle something that a human could actually make use of.
+  // This is mostly in place as a bound on how much work we'll do if we are
+  // asked to demangle an mangled name from an untrusted source, so it should be
+  // much larger than the largest expected symbol, but much smaller than the
+  // amount of work we can do in, e.g., a second.
+  //
+  // Some real-world symbols from an arbitrary binary started failing between
+  // 2^12 and 2^13, so we multiply the latter by an extra factor of 16 to set
+  // the limit.
+  //
+  // Spending one second on 2^17 parse steps would require each step to take
+  // 7.6us, or ~30000 clock cycles, so it's safe to say this can be done in
+  // under a second.
+  static constexpr int kParseStepsLimit = 1 << 17;
+
+  bool IsTooComplex() const {
+    return state_->recursion_depth > kRecursionDepthLimit ||
+           state_->steps > kParseStepsLimit;
+  }
+
+ private:
+  State *state_;
+};
+}  // namespace
+
+// We don't use strlen() in libc since it's not guaranteed to be async
+// signal safe.
+static size_t StrLen(const char *str) {
+  size_t len = 0;
+  while (*str != '\0') {
+    ++str;
+    ++len;
+  }
+  return len;
+}
+
+// Returns true if "str" has at least "n" characters remaining.
+static bool AtLeastNumCharsRemaining(const char *str, int n) {
+  for (int i = 0; i < n; ++i) {
+    if (str[i] == '\0') {
+      return false;
+    }
+  }
+  return true;
+}
+
+// Returns true if "str" has "prefix" as a prefix.
+static bool StrPrefix(const char *str, const char *prefix) {
+  size_t i = 0;
+  while (str[i] != '\0' && prefix[i] != '\0' && str[i] == prefix[i]) {
+    ++i;
+  }
+  return prefix[i] == '\0';  // Consumed everything in "prefix".
+}
+
+static void InitState(State *state, const char *mangled, char *out,
+                      int out_size) {
+  state->mangled_begin = mangled;
+  state->out = out;
+  state->out_end_idx = out_size;
+  state->recursion_depth = 0;
+  state->steps = 0;
+
+  state->parse_state.mangled_idx = 0;
+  state->parse_state.out_cur_idx = 0;
+  state->parse_state.prev_name_idx = 0;
+  state->parse_state.prev_name_length = -1;
+  state->parse_state.nest_level = -1;
+  state->parse_state.append = true;
+}
+
+static inline const char *RemainingInput(State *state) {
+  return &state->mangled_begin[state->parse_state.mangled_idx];
+}
+
+// Returns true and advances "mangled_idx" if we find "one_char_token"
+// at "mangled_idx" position.  It is assumed that "one_char_token" does
+// not contain '\0'.
+static bool ParseOneCharToken(State *state, const char one_char_token) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (RemainingInput(state)[0] == one_char_token) {
+    ++state->parse_state.mangled_idx;
+    return true;
+  }
+  return false;
+}
+
+// Returns true and advances "mangled_cur" if we find "two_char_token"
+// at "mangled_cur" position.  It is assumed that "two_char_token" does
+// not contain '\0'.
+static bool ParseTwoCharToken(State *state, const char *two_char_token) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (RemainingInput(state)[0] == two_char_token[0] &&
+      RemainingInput(state)[1] == two_char_token[1]) {
+    state->parse_state.mangled_idx += 2;
+    return true;
+  }
+  return false;
+}
+
+// Returns true and advances "mangled_cur" if we find any character in
+// "char_class" at "mangled_cur" position.
+static bool ParseCharClass(State *state, const char *char_class) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (RemainingInput(state)[0] == '\0') {
+    return false;
+  }
+  const char *p = char_class;
+  for (; *p != '\0'; ++p) {
+    if (RemainingInput(state)[0] == *p) {
+      ++state->parse_state.mangled_idx;
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool ParseDigit(State *state, int *digit) {
+  char c = RemainingInput(state)[0];
+  if (ParseCharClass(state, "0123456789")) {
+    if (digit != nullptr) {
+      *digit = c - '0';
+    }
+    return true;
+  }
+  return false;
+}
+
+// This function is used for handling an optional non-terminal.
+static bool Optional(bool /*status*/) { return true; }
+
+// This function is used for handling <non-terminal>+ syntax.
+typedef bool (*ParseFunc)(State *);
+static bool OneOrMore(ParseFunc parse_func, State *state) {
+  if (parse_func(state)) {
+    while (parse_func(state)) {
+    }
+    return true;
+  }
+  return false;
+}
+
+// This function is used for handling <non-terminal>* syntax. The function
+// always returns true and must be followed by a termination token or a
+// terminating sequence not handled by parse_func (e.g.
+// ParseOneCharToken(state, 'E')).
+static bool ZeroOrMore(ParseFunc parse_func, State *state) {
+  while (parse_func(state)) {
+  }
+  return true;
+}
+
+// Append "str" at "out_cur_idx".  If there is an overflow, out_cur_idx is
+// set to out_end_idx+1.  The output string is ensured to
+// always terminate with '\0' as long as there is no overflow.
+static void Append(State *state, const char *const str, const int length) {
+  for (int i = 0; i < length; ++i) {
+    if (state->parse_state.out_cur_idx + 1 <
+        state->out_end_idx) {  // +1 for '\0'
+      state->out[state->parse_state.out_cur_idx++] = str[i];
+    } else {
+      // signal overflow
+      state->parse_state.out_cur_idx = state->out_end_idx + 1;
+      break;
+    }
+  }
+  if (state->parse_state.out_cur_idx < state->out_end_idx) {
+    state->out[state->parse_state.out_cur_idx] =
+        '\0';  // Terminate it with '\0'
+  }
+}
+
+// We don't use equivalents in libc to avoid locale issues.
+static bool IsLower(char c) { return c >= 'a' && c <= 'z'; }
+
+static bool IsAlpha(char c) {
+  return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
+}
+
+static bool IsDigit(char c) { return c >= '0' && c <= '9'; }
+
+// Returns true if "str" is a function clone suffix.  These suffixes are used
+// by GCC 4.5.x and later versions (and our locally-modified version of GCC
+// 4.4.x) to indicate functions which have been cloned during optimization.
+// We treat any sequence (.<alpha>+.<digit>+)+ as a function clone suffix.
+static bool IsFunctionCloneSuffix(const char *str) {
+  size_t i = 0;
+  while (str[i] != '\0') {
+    // Consume a single .<alpha>+.<digit>+ sequence.
+    if (str[i] != '.' || !IsAlpha(str[i + 1])) {
+      return false;
+    }
+    i += 2;
+    while (IsAlpha(str[i])) {
+      ++i;
+    }
+    if (str[i] != '.' || !IsDigit(str[i + 1])) {
+      return false;
+    }
+    i += 2;
+    while (IsDigit(str[i])) {
+      ++i;
+    }
+  }
+  return true;  // Consumed everything in "str".
+}
+
+static bool EndsWith(State *state, const char chr) {
+  return state->parse_state.out_cur_idx > 0 &&
+         chr == state->out[state->parse_state.out_cur_idx - 1];
+}
+
+// Append "str" with some tweaks, iff "append" state is true.
+static void MaybeAppendWithLength(State *state, const char *const str,
+                                  const int length) {
+  if (state->parse_state.append && length > 0) {
+    // Append a space if the output buffer ends with '<' and "str"
+    // starts with '<' to avoid <<<.
+    if (str[0] == '<' && EndsWith(state, '<')) {
+      Append(state, " ", 1);
+    }
+    // Remember the last identifier name for ctors/dtors.
+    if (IsAlpha(str[0]) || str[0] == '_') {
+      state->parse_state.prev_name_idx = state->parse_state.out_cur_idx;
+      state->parse_state.prev_name_length = length;
+    }
+    Append(state, str, length);
+  }
+}
+
+// Appends a positive decimal number to the output if appending is enabled.
+static bool MaybeAppendDecimal(State *state, unsigned int val) {
+  // Max {32-64}-bit unsigned int is 20 digits.
+  constexpr size_t kMaxLength = 20;
+  char buf[kMaxLength];
+
+  // We can't use itoa or sprintf as neither is specified to be
+  // async-signal-safe.
+  if (state->parse_state.append) {
+    // We can't have a one-before-the-beginning pointer, so instead start with
+    // one-past-the-end and manipulate one character before the pointer.
+    char *p = &buf[kMaxLength];
+    do {  // val=0 is the only input that should write a leading zero digit.
+      *--p = (val % 10) + '0';
+      val /= 10;
+    } while (p > buf && val != 0);
+
+    // 'p' landed on the last character we set.  How convenient.
+    Append(state, p, kMaxLength - (p - buf));
+  }
+
+  return true;
+}
+
+// A convenient wrapper around MaybeAppendWithLength().
+// Returns true so that it can be placed in "if" conditions.
+static bool MaybeAppend(State *state, const char *const str) {
+  if (state->parse_state.append) {
+    int length = StrLen(str);
+    MaybeAppendWithLength(state, str, length);
+  }
+  return true;
+}
+
+// This function is used for handling nested names.
+static bool EnterNestedName(State *state) {
+  state->parse_state.nest_level = 0;
+  return true;
+}
+
+// This function is used for handling nested names.
+static bool LeaveNestedName(State *state, int16_t prev_value) {
+  state->parse_state.nest_level = prev_value;
+  return true;
+}
+
+// Disable the append mode not to print function parameters, etc.
+static bool DisableAppend(State *state) {
+  state->parse_state.append = false;
+  return true;
+}
+
+// Restore the append mode to the previous state.
+static bool RestoreAppend(State *state, bool prev_value) {
+  state->parse_state.append = prev_value;
+  return true;
+}
+
+// Increase the nest level for nested names.
+static void MaybeIncreaseNestLevel(State *state) {
+  if (state->parse_state.nest_level > -1) {
+    ++state->parse_state.nest_level;
+  }
+}
+
+// Appends :: for nested names if necessary.
+static void MaybeAppendSeparator(State *state) {
+  if (state->parse_state.nest_level >= 1) {
+    MaybeAppend(state, "::");
+  }
+}
+
+// Cancel the last separator if necessary.
+static void MaybeCancelLastSeparator(State *state) {
+  if (state->parse_state.nest_level >= 1 && state->parse_state.append &&
+      state->parse_state.out_cur_idx >= 2) {
+    state->parse_state.out_cur_idx -= 2;
+    state->out[state->parse_state.out_cur_idx] = '\0';
+  }
+}
+
+// Returns true if the identifier of the given length pointed to by
+// "mangled_cur" is anonymous namespace.
+static bool IdentifierIsAnonymousNamespace(State *state, int length) {
+  // Returns true if "anon_prefix" is a proper prefix of "mangled_cur".
+  static const char anon_prefix[] = "_GLOBAL__N_";
+  return (length > static_cast<int>(sizeof(anon_prefix) - 1) &&
+          StrPrefix(RemainingInput(state), anon_prefix));
+}
+
+// Forward declarations of our parsing functions.
+static bool ParseMangledName(State *state);
+static bool ParseEncoding(State *state);
+static bool ParseName(State *state);
+static bool ParseUnscopedName(State *state);
+static bool ParseNestedName(State *state);
+static bool ParsePrefix(State *state);
+static bool ParseUnqualifiedName(State *state);
+static bool ParseSourceName(State *state);
+static bool ParseLocalSourceName(State *state);
+static bool ParseUnnamedTypeName(State *state);
+static bool ParseNumber(State *state, int *number_out);
+static bool ParseFloatNumber(State *state);
+static bool ParseSeqId(State *state);
+static bool ParseIdentifier(State *state, int length);
+static bool ParseOperatorName(State *state, int *arity);
+static bool ParseSpecialName(State *state);
+static bool ParseCallOffset(State *state);
+static bool ParseNVOffset(State *state);
+static bool ParseVOffset(State *state);
+static bool ParseCtorDtorName(State *state);
+static bool ParseDecltype(State *state);
+static bool ParseType(State *state);
+static bool ParseCVQualifiers(State *state);
+static bool ParseBuiltinType(State *state);
+static bool ParseFunctionType(State *state);
+static bool ParseBareFunctionType(State *state);
+static bool ParseClassEnumType(State *state);
+static bool ParseArrayType(State *state);
+static bool ParsePointerToMemberType(State *state);
+static bool ParseTemplateParam(State *state);
+static bool ParseTemplateTemplateParam(State *state);
+static bool ParseTemplateArgs(State *state);
+static bool ParseTemplateArg(State *state);
+static bool ParseBaseUnresolvedName(State *state);
+static bool ParseUnresolvedName(State *state);
+static bool ParseExpression(State *state);
+static bool ParseExprPrimary(State *state);
+static bool ParseExprCastValue(State *state);
+static bool ParseLocalName(State *state);
+static bool ParseLocalNameSuffix(State *state);
+static bool ParseDiscriminator(State *state);
+static bool ParseSubstitution(State *state, bool accept_std);
+
+// Implementation note: the following code is a straightforward
+// translation of the Itanium C++ ABI defined in BNF with a couple of
+// exceptions.
+//
+// - Support GNU extensions not defined in the Itanium C++ ABI
+// - <prefix> and <template-prefix> are combined to avoid infinite loop
+// - Reorder patterns to shorten the code
+// - Reorder patterns to give greedier functions precedence
+//   We'll mark "Less greedy than" for these cases in the code
+//
+// Each parsing function changes the parse state and returns true on
+// success, or returns false and doesn't change the parse state (note:
+// the parse-steps counter increases regardless of success or failure).
+// To ensure that the parse state isn't changed in the latter case, we
+// save the original state before we call multiple parsing functions
+// consecutively with &&, and restore it if unsuccessful.  See
+// ParseEncoding() as an example of this convention.  We follow the
+// convention throughout the code.
+//
+// Originally we tried to do demangling without following the full ABI
+// syntax but it turned out we needed to follow the full syntax to
+// parse complicated cases like nested template arguments.  Note that
+// implementing a full-fledged demangler isn't trivial (libiberty's
+// cp-demangle.c has +4300 lines).
+//
+// Note that (foo) in <(foo) ...> is a modifier to be ignored.
+//
+// Reference:
+// - Itanium C++ ABI
+//   <https://mentorembedded.github.io/cxx-abi/abi.html#mangling>
+
+// <mangled-name> ::= _Z <encoding>
+static bool ParseMangledName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  return ParseTwoCharToken(state, "_Z") && ParseEncoding(state);
+}
+
+// <encoding> ::= <(function) name> <bare-function-type>
+//            ::= <(data) name>
+//            ::= <special-name>
+static bool ParseEncoding(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  // Implementing the first two productions together as <name>
+  // [<bare-function-type>] avoids exponential blowup of backtracking.
+  //
+  // Since Optional(...) can't fail, there's no need to copy the state for
+  // backtracking.
+  if (ParseName(state) && Optional(ParseBareFunctionType(state))) {
+    return true;
+  }
+
+  if (ParseSpecialName(state)) {
+    return true;
+  }
+  return false;
+}
+
+// <name> ::= <nested-name>
+//        ::= <unscoped-template-name> <template-args>
+//        ::= <unscoped-name>
+//        ::= <local-name>
+static bool ParseName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (ParseNestedName(state) || ParseLocalName(state)) {
+    return true;
+  }
+
+  // We reorganize the productions to avoid re-parsing unscoped names.
+  // - Inline <unscoped-template-name> productions:
+  //   <name> ::= <substitution> <template-args>
+  //          ::= <unscoped-name> <template-args>
+  //          ::= <unscoped-name>
+  // - Merge the two productions that start with unscoped-name:
+  //   <name> ::= <unscoped-name> [<template-args>]
+
+  ParseState copy = state->parse_state;
+  // "std<...>" isn't a valid name.
+  if (ParseSubstitution(state, /*accept_std=*/false) &&
+      ParseTemplateArgs(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Note there's no need to restore state after this since only the first
+  // subparser can fail.
+  return ParseUnscopedName(state) && Optional(ParseTemplateArgs(state));
+}
+
+// <unscoped-name> ::= <unqualified-name>
+//                 ::= St <unqualified-name>
+static bool ParseUnscopedName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (ParseUnqualifiedName(state)) {
+    return true;
+  }
+
+  ParseState copy = state->parse_state;
+  if (ParseTwoCharToken(state, "St") && MaybeAppend(state, "std::") &&
+      ParseUnqualifiedName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <ref-qualifer> ::= R // lvalue method reference qualifier
+//                ::= O // rvalue method reference qualifier
+static inline bool ParseRefQualifier(State *state) {
+  return ParseCharClass(state, "OR");
+}
+
+// <nested-name> ::= N [<CV-qualifiers>] [<ref-qualifier>] <prefix>
+//                   <unqualified-name> E
+//               ::= N [<CV-qualifiers>] [<ref-qualifier>] <template-prefix>
+//                   <template-args> E
+static bool ParseNestedName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'N') && EnterNestedName(state) &&
+      Optional(ParseCVQualifiers(state)) &&
+      Optional(ParseRefQualifier(state)) && ParsePrefix(state) &&
+      LeaveNestedName(state, copy.nest_level) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// This part is tricky.  If we literally translate them to code, we'll
+// end up infinite loop.  Hence we merge them to avoid the case.
+//
+// <prefix> ::= <prefix> <unqualified-name>
+//          ::= <template-prefix> <template-args>
+//          ::= <template-param>
+//          ::= <substitution>
+//          ::= # empty
+// <template-prefix> ::= <prefix> <(template) unqualified-name>
+//                   ::= <template-param>
+//                   ::= <substitution>
+static bool ParsePrefix(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  bool has_something = false;
+  while (true) {
+    MaybeAppendSeparator(state);
+    if (ParseTemplateParam(state) ||
+        ParseSubstitution(state, /*accept_std=*/true) ||
+        ParseUnscopedName(state) ||
+        (ParseOneCharToken(state, 'M') && ParseUnnamedTypeName(state))) {
+      has_something = true;
+      MaybeIncreaseNestLevel(state);
+      continue;
+    }
+    MaybeCancelLastSeparator(state);
+    if (has_something && ParseTemplateArgs(state)) {
+      return ParsePrefix(state);
+    } else {
+      break;
+    }
+  }
+  return true;
+}
+
+// <unqualified-name> ::= <operator-name>
+//                    ::= <ctor-dtor-name>
+//                    ::= <source-name>
+//                    ::= <local-source-name> // GCC extension; see below.
+//                    ::= <unnamed-type-name>
+static bool ParseUnqualifiedName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  return (ParseOperatorName(state, nullptr) || ParseCtorDtorName(state) ||
+          ParseSourceName(state) || ParseLocalSourceName(state) ||
+          ParseUnnamedTypeName(state));
+}
+
+// <source-name> ::= <positive length number> <identifier>
+static bool ParseSourceName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  int length = -1;
+  if (ParseNumber(state, &length) && ParseIdentifier(state, length)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <local-source-name> ::= L <source-name> [<discriminator>]
+//
+// References:
+//   https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31775
+//   https://gcc.gnu.org/viewcvs?view=rev&revision=124467
+static bool ParseLocalSourceName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'L') && ParseSourceName(state) &&
+      Optional(ParseDiscriminator(state))) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <unnamed-type-name> ::= Ut [<(nonnegative) number>] _
+//                     ::= <closure-type-name>
+// <closure-type-name> ::= Ul <lambda-sig> E [<(nonnegative) number>] _
+// <lambda-sig>        ::= <(parameter) type>+
+static bool ParseUnnamedTypeName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  // Type's 1-based index n is encoded as { "", n == 1; itoa(n-2), otherwise }.
+  // Optionally parse the encoded value into 'which' and add 2 to get the index.
+  int which = -1;
+
+  // Unnamed type local to function or class.
+  if (ParseTwoCharToken(state, "Ut") && Optional(ParseNumber(state, &which)) &&
+      which <= std::numeric_limits<int>::max() - 2 &&  // Don't overflow.
+      ParseOneCharToken(state, '_')) {
+    MaybeAppend(state, "{unnamed type#");
+    MaybeAppendDecimal(state, 2 + which);
+    MaybeAppend(state, "}");
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Closure type.
+  which = -1;
+  if (ParseTwoCharToken(state, "Ul") && DisableAppend(state) &&
+      OneOrMore(ParseType, state) && RestoreAppend(state, copy.append) &&
+      ParseOneCharToken(state, 'E') && Optional(ParseNumber(state, &which)) &&
+      which <= std::numeric_limits<int>::max() - 2 &&  // Don't overflow.
+      ParseOneCharToken(state, '_')) {
+    MaybeAppend(state, "{lambda()#");
+    MaybeAppendDecimal(state, 2 + which);
+    MaybeAppend(state, "}");
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <number> ::= [n] <non-negative decimal integer>
+// If "number_out" is non-null, then *number_out is set to the value of the
+// parsed number on success.
+static bool ParseNumber(State *state, int *number_out) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  bool negative = false;
+  if (ParseOneCharToken(state, 'n')) {
+    negative = true;
+  }
+  const char *p = RemainingInput(state);
+  uint64_t number = 0;
+  for (; *p != '\0'; ++p) {
+    if (IsDigit(*p)) {
+      number = number * 10 + (*p - '0');
+    } else {
+      break;
+    }
+  }
+  // Apply the sign with uint64_t arithmetic so overflows aren't UB.  Gives
+  // "incorrect" results for out-of-range inputs, but negative values only
+  // appear for literals, which aren't printed.
+  if (negative) {
+    number = ~number + 1;
+  }
+  if (p != RemainingInput(state)) {  // Conversion succeeded.
+    state->parse_state.mangled_idx += p - RemainingInput(state);
+    if (number_out != nullptr) {
+      // Note: possibly truncate "number".
+      *number_out = number;
+    }
+    return true;
+  }
+  return false;
+}
+
+// Floating-point literals are encoded using a fixed-length lowercase
+// hexadecimal string.
+static bool ParseFloatNumber(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  const char *p = RemainingInput(state);
+  for (; *p != '\0'; ++p) {
+    if (!IsDigit(*p) && !(*p >= 'a' && *p <= 'f')) {
+      break;
+    }
+  }
+  if (p != RemainingInput(state)) {  // Conversion succeeded.
+    state->parse_state.mangled_idx += p - RemainingInput(state);
+    return true;
+  }
+  return false;
+}
+
+// The <seq-id> is a sequence number in base 36,
+// using digits and upper case letters
+static bool ParseSeqId(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  const char *p = RemainingInput(state);
+  for (; *p != '\0'; ++p) {
+    if (!IsDigit(*p) && !(*p >= 'A' && *p <= 'Z')) {
+      break;
+    }
+  }
+  if (p != RemainingInput(state)) {  // Conversion succeeded.
+    state->parse_state.mangled_idx += p - RemainingInput(state);
+    return true;
+  }
+  return false;
+}
+
+// <identifier> ::= <unqualified source code identifier> (of given length)
+static bool ParseIdentifier(State *state, int length) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (length < 0 || !AtLeastNumCharsRemaining(RemainingInput(state), length)) {
+    return false;
+  }
+  if (IdentifierIsAnonymousNamespace(state, length)) {
+    MaybeAppend(state, "(anonymous namespace)");
+  } else {
+    MaybeAppendWithLength(state, RemainingInput(state), length);
+  }
+  state->parse_state.mangled_idx += length;
+  return true;
+}
+
+// <operator-name> ::= nw, and other two letters cases
+//                 ::= cv <type>  # (cast)
+//                 ::= v  <digit> <source-name> # vendor extended operator
+static bool ParseOperatorName(State *state, int *arity) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (!AtLeastNumCharsRemaining(RemainingInput(state), 2)) {
+    return false;
+  }
+  // First check with "cv" (cast) case.
+  ParseState copy = state->parse_state;
+  if (ParseTwoCharToken(state, "cv") && MaybeAppend(state, "operator ") &&
+      EnterNestedName(state) && ParseType(state) &&
+      LeaveNestedName(state, copy.nest_level)) {
+    if (arity != nullptr) {
+      *arity = 1;
+    }
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Then vendor extended operators.
+  if (ParseOneCharToken(state, 'v') && ParseDigit(state, arity) &&
+      ParseSourceName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Other operator names should start with a lower alphabet followed
+  // by a lower/upper alphabet.
+  if (!(IsLower(RemainingInput(state)[0]) &&
+        IsAlpha(RemainingInput(state)[1]))) {
+    return false;
+  }
+  // We may want to perform a binary search if we really need speed.
+  const AbbrevPair *p;
+  for (p = kOperatorList; p->abbrev != nullptr; ++p) {
+    if (RemainingInput(state)[0] == p->abbrev[0] &&
+        RemainingInput(state)[1] == p->abbrev[1]) {
+      if (arity != nullptr) {
+        *arity = p->arity;
+      }
+      MaybeAppend(state, "operator");
+      if (IsLower(*p->real_name)) {  // new, delete, etc.
+        MaybeAppend(state, " ");
+      }
+      MaybeAppend(state, p->real_name);
+      state->parse_state.mangled_idx += 2;
+      return true;
+    }
+  }
+  return false;
+}
+
+// <special-name> ::= TV <type>
+//                ::= TT <type>
+//                ::= TI <type>
+//                ::= TS <type>
+//                ::= Tc <call-offset> <call-offset> <(base) encoding>
+//                ::= GV <(object) name>
+//                ::= T <call-offset> <(base) encoding>
+// G++ extensions:
+//                ::= TC <type> <(offset) number> _ <(base) type>
+//                ::= TF <type>
+//                ::= TJ <type>
+//                ::= GR <name>
+//                ::= GA <encoding>
+//                ::= Th <call-offset> <(base) encoding>
+//                ::= Tv <call-offset> <(base) encoding>
+//
+// Note: we don't care much about them since they don't appear in
+// stack traces.  The are special data.
+static bool ParseSpecialName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'T') && ParseCharClass(state, "VTIS") &&
+      ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "Tc") && ParseCallOffset(state) &&
+      ParseCallOffset(state) && ParseEncoding(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "GV") && ParseName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'T') && ParseCallOffset(state) &&
+      ParseEncoding(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // G++ extensions
+  if (ParseTwoCharToken(state, "TC") && ParseType(state) &&
+      ParseNumber(state, nullptr) && ParseOneCharToken(state, '_') &&
+      DisableAppend(state) && ParseType(state)) {
+    RestoreAppend(state, copy.append);
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'T') && ParseCharClass(state, "FJ") &&
+      ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "GR") && ParseName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "GA") && ParseEncoding(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'T') && ParseCharClass(state, "hv") &&
+      ParseCallOffset(state) && ParseEncoding(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <call-offset> ::= h <nv-offset> _
+//               ::= v <v-offset> _
+static bool ParseCallOffset(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'h') && ParseNVOffset(state) &&
+      ParseOneCharToken(state, '_')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'v') && ParseVOffset(state) &&
+      ParseOneCharToken(state, '_')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <nv-offset> ::= <(offset) number>
+static bool ParseNVOffset(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  return ParseNumber(state, nullptr);
+}
+
+// <v-offset>  ::= <(offset) number> _ <(virtual offset) number>
+static bool ParseVOffset(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseNumber(state, nullptr) && ParseOneCharToken(state, '_') &&
+      ParseNumber(state, nullptr)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <ctor-dtor-name> ::= C1 | C2 | C3
+//                  ::= D0 | D1 | D2
+// # GCC extensions: "unified" constructor/destructor.  See
+// # https://github.com/gcc-mirror/gcc/blob/7ad17b583c3643bd4557f29b8391ca7ef08391f5/gcc/cp/mangle.c#L1847
+//                  ::= C4 | D4
+static bool ParseCtorDtorName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'C') && ParseCharClass(state, "1234")) {
+    const char *const prev_name = state->out + state->parse_state.prev_name_idx;
+    MaybeAppendWithLength(state, prev_name,
+                          state->parse_state.prev_name_length);
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'D') && ParseCharClass(state, "0124")) {
+    const char *const prev_name = state->out + state->parse_state.prev_name_idx;
+    MaybeAppend(state, "~");
+    MaybeAppendWithLength(state, prev_name,
+                          state->parse_state.prev_name_length);
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <decltype> ::= Dt <expression> E  # decltype of an id-expression or class
+//                                   # member access (C++0x)
+//            ::= DT <expression> E  # decltype of an expression (C++0x)
+static bool ParseDecltype(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'D') && ParseCharClass(state, "tT") &&
+      ParseExpression(state) && ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <type> ::= <CV-qualifiers> <type>
+//        ::= P <type>   # pointer-to
+//        ::= R <type>   # reference-to
+//        ::= O <type>   # rvalue reference-to (C++0x)
+//        ::= C <type>   # complex pair (C 2000)
+//        ::= G <type>   # imaginary (C 2000)
+//        ::= U <source-name> <type>  # vendor extended type qualifier
+//        ::= <builtin-type>
+//        ::= <function-type>
+//        ::= <class-enum-type>  # note: just an alias for <name>
+//        ::= <array-type>
+//        ::= <pointer-to-member-type>
+//        ::= <template-template-param> <template-args>
+//        ::= <template-param>
+//        ::= <decltype>
+//        ::= <substitution>
+//        ::= Dp <type>          # pack expansion of (C++0x)
+//
+static bool ParseType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+
+  // We should check CV-qualifers, and PRGC things first.
+  //
+  // CV-qualifiers overlap with some operator names, but an operator name is not
+  // valid as a type.  To avoid an ambiguity that can lead to exponential time
+  // complexity, refuse to backtrack the CV-qualifiers.
+  //
+  // _Z4aoeuIrMvvE
+  //  => _Z 4aoeuI        rM  v     v   E
+  //         aoeu<operator%=, void, void>
+  //  => _Z 4aoeuI r Mv v              E
+  //         aoeu<void void::* restrict>
+  //
+  // By consuming the CV-qualifiers first, the former parse is disabled.
+  if (ParseCVQualifiers(state)) {
+    const bool result = ParseType(state);
+    if (!result) state->parse_state = copy;
+    return result;
+  }
+  state->parse_state = copy;
+
+  // Similarly, these tag characters can overlap with other <name>s resulting in
+  // two different parse prefixes that land on <template-args> in the same
+  // place, such as "C3r1xI...".  So, disable the "ctor-name = C3" parse by
+  // refusing to backtrack the tag characters.
+  if (ParseCharClass(state, "OPRCG")) {
+    const bool result = ParseType(state);
+    if (!result) state->parse_state = copy;
+    return result;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "Dp") && ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'U') && ParseSourceName(state) &&
+      ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseBuiltinType(state) || ParseFunctionType(state) ||
+      ParseClassEnumType(state) || ParseArrayType(state) ||
+      ParsePointerToMemberType(state) || ParseDecltype(state) ||
+      // "std" on its own isn't a type.
+      ParseSubstitution(state, /*accept_std=*/false)) {
+    return true;
+  }
+
+  if (ParseTemplateTemplateParam(state) && ParseTemplateArgs(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Less greedy than <template-template-param> <template-args>.
+  if (ParseTemplateParam(state)) {
+    return true;
+  }
+
+  return false;
+}
+
+// <CV-qualifiers> ::= [r] [V] [K]
+// We don't allow empty <CV-qualifiers> to avoid infinite loop in
+// ParseType().
+static bool ParseCVQualifiers(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  int num_cv_qualifiers = 0;
+  num_cv_qualifiers += ParseOneCharToken(state, 'r');
+  num_cv_qualifiers += ParseOneCharToken(state, 'V');
+  num_cv_qualifiers += ParseOneCharToken(state, 'K');
+  return num_cv_qualifiers > 0;
+}
+
+// <builtin-type> ::= v, etc.  # single-character builtin types
+//                ::= u <source-name>
+//                ::= Dd, etc.  # two-character builtin types
+//
+// Not supported:
+//                ::= DF <number> _ # _FloatN (N bits)
+//
+static bool ParseBuiltinType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  const AbbrevPair *p;
+  for (p = kBuiltinTypeList; p->abbrev != nullptr; ++p) {
+    // Guaranteed only 1- or 2-character strings in kBuiltinTypeList.
+    if (p->abbrev[1] == '\0') {
+      if (ParseOneCharToken(state, p->abbrev[0])) {
+        MaybeAppend(state, p->real_name);
+        return true;
+      }
+    } else if (p->abbrev[2] == '\0' && ParseTwoCharToken(state, p->abbrev)) {
+      MaybeAppend(state, p->real_name);
+      return true;
+    }
+  }
+
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'u') && ParseSourceName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <function-type> ::= F [Y] <bare-function-type> E
+static bool ParseFunctionType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'F') &&
+      Optional(ParseOneCharToken(state, 'Y')) && ParseBareFunctionType(state) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <bare-function-type> ::= <(signature) type>+
+static bool ParseBareFunctionType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  DisableAppend(state);
+  if (OneOrMore(ParseType, state)) {
+    RestoreAppend(state, copy.append);
+    MaybeAppend(state, "()");
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <class-enum-type> ::= <name>
+static bool ParseClassEnumType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  return ParseName(state);
+}
+
+// <array-type> ::= A <(positive dimension) number> _ <(element) type>
+//              ::= A [<(dimension) expression>] _ <(element) type>
+static bool ParseArrayType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'A') && ParseNumber(state, nullptr) &&
+      ParseOneCharToken(state, '_') && ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'A') && Optional(ParseExpression(state)) &&
+      ParseOneCharToken(state, '_') && ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <pointer-to-member-type> ::= M <(class) type> <(member) type>
+static bool ParsePointerToMemberType(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'M') && ParseType(state) && ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <template-param> ::= T_
+//                  ::= T <parameter-2 non-negative number> _
+static bool ParseTemplateParam(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (ParseTwoCharToken(state, "T_")) {
+    MaybeAppend(state, "?");  // We don't support template substitutions.
+    return true;
+  }
+
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'T') && ParseNumber(state, nullptr) &&
+      ParseOneCharToken(state, '_')) {
+    MaybeAppend(state, "?");  // We don't support template substitutions.
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <template-template-param> ::= <template-param>
+//                           ::= <substitution>
+static bool ParseTemplateTemplateParam(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  return (ParseTemplateParam(state) ||
+          // "std" on its own isn't a template.
+          ParseSubstitution(state, /*accept_std=*/false));
+}
+
+// <template-args> ::= I <template-arg>+ E
+static bool ParseTemplateArgs(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  DisableAppend(state);
+  if (ParseOneCharToken(state, 'I') && OneOrMore(ParseTemplateArg, state) &&
+      ParseOneCharToken(state, 'E')) {
+    RestoreAppend(state, copy.append);
+    MaybeAppend(state, "<>");
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <template-arg>  ::= <type>
+//                 ::= <expr-primary>
+//                 ::= J <template-arg>* E        # argument pack
+//                 ::= X <expression> E
+static bool ParseTemplateArg(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'J') && ZeroOrMore(ParseTemplateArg, state) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // There can be significant overlap between the following leading to
+  // exponential backtracking:
+  //
+  //   <expr-primary> ::= L <type> <expr-cast-value> E
+  //                 e.g. L 2xxIvE 1                 E
+  //   <type>         ==> <local-source-name> <template-args>
+  //                 e.g. L 2xx               IvE
+  //
+  // This means parsing an entire <type> twice, and <type> can contain
+  // <template-arg>, so this can generate exponential backtracking.  There is
+  // only overlap when the remaining input starts with "L <source-name>", so
+  // parse all cases that can start this way jointly to share the common prefix.
+  //
+  // We have:
+  //
+  //   <template-arg> ::= <type>
+  //                  ::= <expr-primary>
+  //
+  // First, drop all the productions of <type> that must start with something
+  // other than 'L'.  All that's left is <class-enum-type>; inline it.
+  //
+  //   <type> ::= <nested-name> # starts with 'N'
+  //          ::= <unscoped-name>
+  //          ::= <unscoped-template-name> <template-args>
+  //          ::= <local-name> # starts with 'Z'
+  //
+  // Drop and inline again:
+  //
+  //   <type> ::= <unscoped-name>
+  //          ::= <unscoped-name> <template-args>
+  //          ::= <substitution> <template-args> # starts with 'S'
+  //
+  // Merge the first two, inline <unscoped-name>, drop last:
+  //
+  //   <type> ::= <unqualified-name> [<template-args>]
+  //          ::= St <unqualified-name> [<template-args>] # starts with 'S'
+  //
+  // Drop and inline:
+  //
+  //   <type> ::= <operator-name> [<template-args>] # starts with lowercase
+  //          ::= <ctor-dtor-name> [<template-args>] # starts with 'C' or 'D'
+  //          ::= <source-name> [<template-args>] # starts with digit
+  //          ::= <local-source-name> [<template-args>]
+  //          ::= <unnamed-type-name> [<template-args>] # starts with 'U'
+  //
+  // One more time:
+  //
+  //   <type> ::= L <source-name> [<template-args>]
+  //
+  // Likewise with <expr-primary>:
+  //
+  //   <expr-primary> ::= L <type> <expr-cast-value> E
+  //                  ::= LZ <encoding> E # cannot overlap; drop
+  //                  ::= L <mangled_name> E # cannot overlap; drop
+  //
+  // By similar reasoning as shown above, the only <type>s starting with
+  // <source-name> are "<source-name> [<template-args>]".  Inline this.
+  //
+  //   <expr-primary> ::= L <source-name> [<template-args>] <expr-cast-value> E
+  //
+  // Now inline both of these into <template-arg>:
+  //
+  //   <template-arg> ::= L <source-name> [<template-args>]
+  //                  ::= L <source-name> [<template-args>] <expr-cast-value> E
+  //
+  // Merge them and we're done:
+  //   <template-arg>
+  //     ::= L <source-name> [<template-args>] [<expr-cast-value> E]
+  if (ParseLocalSourceName(state) && Optional(ParseTemplateArgs(state))) {
+    copy = state->parse_state;
+    if (ParseExprCastValue(state) && ParseOneCharToken(state, 'E')) {
+      return true;
+    }
+    state->parse_state = copy;
+    return true;
+  }
+
+  // Now that the overlapping cases can't reach this code, we can safely call
+  // both of these.
+  if (ParseType(state) || ParseExprPrimary(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'X') && ParseExpression(state) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <unresolved-type> ::= <template-param> [<template-args>]
+//                   ::= <decltype>
+//                   ::= <substitution>
+static inline bool ParseUnresolvedType(State *state) {
+  // No ComplexityGuard because we don't copy the state in this stack frame.
+  return (ParseTemplateParam(state) && Optional(ParseTemplateArgs(state))) ||
+         ParseDecltype(state) || ParseSubstitution(state, /*accept_std=*/false);
+}
+
+// <simple-id> ::= <source-name> [<template-args>]
+static inline bool ParseSimpleId(State *state) {
+  // No ComplexityGuard because we don't copy the state in this stack frame.
+
+  // Note: <simple-id> cannot be followed by a parameter pack; see comment in
+  // ParseUnresolvedType.
+  return ParseSourceName(state) && Optional(ParseTemplateArgs(state));
+}
+
+// <base-unresolved-name> ::= <source-name> [<template-args>]
+//                        ::= on <operator-name> [<template-args>]
+//                        ::= dn <destructor-name>
+static bool ParseBaseUnresolvedName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+
+  if (ParseSimpleId(state)) {
+    return true;
+  }
+
+  ParseState copy = state->parse_state;
+  if (ParseTwoCharToken(state, "on") && ParseOperatorName(state, nullptr) &&
+      Optional(ParseTemplateArgs(state))) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "dn") &&
+      (ParseUnresolvedType(state) || ParseSimpleId(state))) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <unresolved-name> ::= [gs] <base-unresolved-name>
+//                   ::= sr <unresolved-type> <base-unresolved-name>
+//                   ::= srN <unresolved-type> <unresolved-qualifier-level>+ E
+//                         <base-unresolved-name>
+//                   ::= [gs] sr <unresolved-qualifier-level>+ E
+//                         <base-unresolved-name>
+static bool ParseUnresolvedName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+
+  ParseState copy = state->parse_state;
+  if (Optional(ParseTwoCharToken(state, "gs")) &&
+      ParseBaseUnresolvedName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "sr") && ParseUnresolvedType(state) &&
+      ParseBaseUnresolvedName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseTwoCharToken(state, "sr") && ParseOneCharToken(state, 'N') &&
+      ParseUnresolvedType(state) &&
+      OneOrMore(/* <unresolved-qualifier-level> ::= */ ParseSimpleId, state) &&
+      ParseOneCharToken(state, 'E') && ParseBaseUnresolvedName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (Optional(ParseTwoCharToken(state, "gs")) &&
+      ParseTwoCharToken(state, "sr") &&
+      OneOrMore(/* <unresolved-qualifier-level> ::= */ ParseSimpleId, state) &&
+      ParseOneCharToken(state, 'E') && ParseBaseUnresolvedName(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <expression> ::= <1-ary operator-name> <expression>
+//              ::= <2-ary operator-name> <expression> <expression>
+//              ::= <3-ary operator-name> <expression> <expression> <expression>
+//              ::= cl <expression>+ E
+//              ::= cv <type> <expression>      # type (expression)
+//              ::= cv <type> _ <expression>* E # type (expr-list)
+//              ::= st <type>
+//              ::= <template-param>
+//              ::= <function-param>
+//              ::= <expr-primary>
+//              ::= dt <expression> <unresolved-name> # expr.name
+//              ::= pt <expression> <unresolved-name> # expr->name
+//              ::= sp <expression>         # argument pack expansion
+//              ::= sr <type> <unqualified-name> <template-args>
+//              ::= sr <type> <unqualified-name>
+// <function-param> ::= fp <(top-level) CV-qualifiers> _
+//                  ::= fp <(top-level) CV-qualifiers> <number> _
+//                  ::= fL <number> p <(top-level) CV-qualifiers> _
+//                  ::= fL <number> p <(top-level) CV-qualifiers> <number> _
+static bool ParseExpression(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (ParseTemplateParam(state) || ParseExprPrimary(state)) {
+    return true;
+  }
+
+  // Object/function call expression.
+  ParseState copy = state->parse_state;
+  if (ParseTwoCharToken(state, "cl") && OneOrMore(ParseExpression, state) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Function-param expression (level 0).
+  if (ParseTwoCharToken(state, "fp") && Optional(ParseCVQualifiers(state)) &&
+      Optional(ParseNumber(state, nullptr)) && ParseOneCharToken(state, '_')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Function-param expression (level 1+).
+  if (ParseTwoCharToken(state, "fL") && Optional(ParseNumber(state, nullptr)) &&
+      ParseOneCharToken(state, 'p') && Optional(ParseCVQualifiers(state)) &&
+      Optional(ParseNumber(state, nullptr)) && ParseOneCharToken(state, '_')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Parse the conversion expressions jointly to avoid re-parsing the <type> in
+  // their common prefix.  Parsed as:
+  // <expression> ::= cv <type> <conversion-args>
+  // <conversion-args> ::= _ <expression>* E
+  //                   ::= <expression>
+  //
+  // Also don't try ParseOperatorName after seeing "cv", since ParseOperatorName
+  // also needs to accept "cv <type>" in other contexts.
+  if (ParseTwoCharToken(state, "cv")) {
+    if (ParseType(state)) {
+      ParseState copy2 = state->parse_state;
+      if (ParseOneCharToken(state, '_') && ZeroOrMore(ParseExpression, state) &&
+          ParseOneCharToken(state, 'E')) {
+        return true;
+      }
+      state->parse_state = copy2;
+      if (ParseExpression(state)) {
+        return true;
+      }
+    }
+  } else {
+    // Parse unary, binary, and ternary operator expressions jointly, taking
+    // care not to re-parse subexpressions repeatedly. Parse like:
+    //   <expression> ::= <operator-name> <expression>
+    //                    [<one-to-two-expressions>]
+    //   <one-to-two-expressions> ::= <expression> [<expression>]
+    int arity = -1;
+    if (ParseOperatorName(state, &arity) &&
+        arity > 0 &&  // 0 arity => disabled.
+        (arity < 3 || ParseExpression(state)) &&
+        (arity < 2 || ParseExpression(state)) &&
+        (arity < 1 || ParseExpression(state))) {
+      return true;
+    }
+  }
+  state->parse_state = copy;
+
+  // sizeof type
+  if (ParseTwoCharToken(state, "st") && ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Object and pointer member access expressions.
+  if ((ParseTwoCharToken(state, "dt") || ParseTwoCharToken(state, "pt")) &&
+      ParseExpression(state) && ParseType(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Pointer-to-member access expressions.  This parses the same as a binary
+  // operator, but it's implemented separately because "ds" shouldn't be
+  // accepted in other contexts that parse an operator name.
+  if (ParseTwoCharToken(state, "ds") && ParseExpression(state) &&
+      ParseExpression(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Parameter pack expansion
+  if (ParseTwoCharToken(state, "sp") && ParseExpression(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return ParseUnresolvedName(state);
+}
+
+// <expr-primary> ::= L <type> <(value) number> E
+//                ::= L <type> <(value) float> E
+//                ::= L <mangled-name> E
+//                // A bug in g++'s C++ ABI version 2 (-fabi-version=2).
+//                ::= LZ <encoding> E
+//
+// Warning, subtle: the "bug" LZ production above is ambiguous with the first
+// production where <type> starts with <local-name>, which can lead to
+// exponential backtracking in two scenarios:
+//
+// - When whatever follows the E in the <local-name> in the first production is
+//   not a name, we backtrack the whole <encoding> and re-parse the whole thing.
+//
+// - When whatever follows the <local-name> in the first production is not a
+//   number and this <expr-primary> may be followed by a name, we backtrack the
+//   <name> and re-parse it.
+//
+// Moreover this ambiguity isn't always resolved -- for example, the following
+// has two different parses:
+//
+//   _ZaaILZ4aoeuE1x1EvE
+//   => operator&&<aoeu, x, E, void>
+//   => operator&&<(aoeu::x)(1), void>
+//
+// To resolve this, we just do what GCC's demangler does, and refuse to parse
+// casts to <local-name> types.
+static bool ParseExprPrimary(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+
+  // The "LZ" special case: if we see LZ, we commit to accept "LZ <encoding> E"
+  // or fail, no backtracking.
+  if (ParseTwoCharToken(state, "LZ")) {
+    if (ParseEncoding(state) && ParseOneCharToken(state, 'E')) {
+      return true;
+    }
+
+    state->parse_state = copy;
+    return false;
+  }
+
+  // The merged cast production.
+  if (ParseOneCharToken(state, 'L') && ParseType(state) &&
+      ParseExprCastValue(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseOneCharToken(state, 'L') && ParseMangledName(state) &&
+      ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <number> or <float>, followed by 'E', as described above ParseExprPrimary.
+static bool ParseExprCastValue(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  // We have to be able to backtrack after accepting a number because we could
+  // have e.g. "7fffE", which will accept "7" as a number but then fail to find
+  // the 'E'.
+  ParseState copy = state->parse_state;
+  if (ParseNumber(state, nullptr) && ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  if (ParseFloatNumber(state) && ParseOneCharToken(state, 'E')) {
+    return true;
+  }
+  state->parse_state = copy;
+
+  return false;
+}
+
+// <local-name> ::= Z <(function) encoding> E <(entity) name> [<discriminator>]
+//              ::= Z <(function) encoding> E s [<discriminator>]
+//
+// Parsing a common prefix of these two productions together avoids an
+// exponential blowup of backtracking.  Parse like:
+//   <local-name> := Z <encoding> E <local-name-suffix>
+//   <local-name-suffix> ::= s [<discriminator>]
+//                       ::= <name> [<discriminator>]
+
+static bool ParseLocalNameSuffix(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+
+  if (MaybeAppend(state, "::") && ParseName(state) &&
+      Optional(ParseDiscriminator(state))) {
+    return true;
+  }
+
+  // Since we're not going to overwrite the above "::" by re-parsing the
+  // <encoding> (whose trailing '\0' byte was in the byte now holding the
+  // first ':'), we have to rollback the "::" if the <name> parse failed.
+  if (state->parse_state.append) {
+    state->out[state->parse_state.out_cur_idx - 2] = '\0';
+  }
+
+  return ParseOneCharToken(state, 's') && Optional(ParseDiscriminator(state));
+}
+
+static bool ParseLocalName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'Z') && ParseEncoding(state) &&
+      ParseOneCharToken(state, 'E') && ParseLocalNameSuffix(state)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <discriminator> := _ <(non-negative) number>
+static bool ParseDiscriminator(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, '_') && ParseNumber(state, nullptr)) {
+    return true;
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// <substitution> ::= S_
+//                ::= S <seq-id> _
+//                ::= St, etc.
+//
+// "St" is special in that it's not valid as a standalone name, and it *is*
+// allowed to precede a name without being wrapped in "N...E".  This means that
+// if we accept it on its own, we can accept "St1a" and try to parse
+// template-args, then fail and backtrack, accept "St" on its own, then "1a" as
+// an unqualified name and re-parse the same template-args.  To block this
+// exponential backtracking, we disable it with 'accept_std=false' in
+// problematic contexts.
+static bool ParseSubstitution(State *state, bool accept_std) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (ParseTwoCharToken(state, "S_")) {
+    MaybeAppend(state, "?");  // We don't support substitutions.
+    return true;
+  }
+
+  ParseState copy = state->parse_state;
+  if (ParseOneCharToken(state, 'S') && ParseSeqId(state) &&
+      ParseOneCharToken(state, '_')) {
+    MaybeAppend(state, "?");  // We don't support substitutions.
+    return true;
+  }
+  state->parse_state = copy;
+
+  // Expand abbreviations like "St" => "std".
+  if (ParseOneCharToken(state, 'S')) {
+    const AbbrevPair *p;
+    for (p = kSubstitutionList; p->abbrev != nullptr; ++p) {
+      if (RemainingInput(state)[0] == p->abbrev[1] &&
+          (accept_std || p->abbrev[1] != 't')) {
+        MaybeAppend(state, "std");
+        if (p->real_name[0] != '\0') {
+          MaybeAppend(state, "::");
+          MaybeAppend(state, p->real_name);
+        }
+        ++state->parse_state.mangled_idx;
+        return true;
+      }
+    }
+  }
+  state->parse_state = copy;
+  return false;
+}
+
+// Parse <mangled-name>, optionally followed by either a function-clone suffix
+// or version suffix.  Returns true only if all of "mangled_cur" was consumed.
+static bool ParseTopLevelMangledName(State *state) {
+  ComplexityGuard guard(state);
+  if (guard.IsTooComplex()) return false;
+  if (ParseMangledName(state)) {
+    if (RemainingInput(state)[0] != '\0') {
+      // Drop trailing function clone suffix, if any.
+      if (IsFunctionCloneSuffix(RemainingInput(state))) {
+        return true;
+      }
+      // Append trailing version suffix if any.
+      // ex. _Z3foo@@GLIBCXX_3.4
+      if (RemainingInput(state)[0] == '@') {
+        MaybeAppend(state, RemainingInput(state));
+        return true;
+      }
+      return false;  // Unconsumed suffix.
+    }
+    return true;
+  }
+  return false;
+}
+
+static bool Overflowed(const State *state) {
+  return state->parse_state.out_cur_idx >= state->out_end_idx;
+}
+
+// The demangler entry point.
+bool Demangle(const char *mangled, char *out, int out_size) {
+  State state;
+  InitState(&state, mangled, out, out_size);
+  return ParseTopLevelMangledName(&state) && !Overflowed(&state);
+}
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/internal/demangle.h b/third_party/abseil_cpp/absl/debugging/internal/demangle.h
new file mode 100644
index 000000000000..c314d9bc237c
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/demangle.h
@@ -0,0 +1,71 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// An async-signal-safe and thread-safe demangler for Itanium C++ ABI
+// (aka G++ V3 ABI).
+//
+// The demangler is implemented to be used in async signal handlers to
+// symbolize stack traces.  We cannot use libstdc++'s
+// abi::__cxa_demangle() in such signal handlers since it's not async
+// signal safe (it uses malloc() internally).
+//
+// Note that this demangler doesn't support full demangling.  More
+// specifically, it doesn't print types of function parameters and
+// types of template arguments.  It just skips them.  However, it's
+// still very useful to extract basic information such as class,
+// function, constructor, destructor, and operator names.
+//
+// See the implementation note in demangle.cc if you are interested.
+//
+// Example:
+//
+// | Mangled Name  | The Demangler | abi::__cxa_demangle()
+// |---------------|---------------|-----------------------
+// | _Z1fv         | f()           | f()
+// | _Z1fi         | f()           | f(int)
+// | _Z3foo3bar    | foo()         | foo(bar)
+// | _Z1fIiEvi     | f<>()         | void f<int>(int)
+// | _ZN1N1fE      | N::f          | N::f
+// | _ZN3Foo3BarEv | Foo::Bar()    | Foo::Bar()
+// | _Zrm1XS_"     | operator%()   | operator%(X, X)
+// | _ZN3FooC1Ev   | Foo::Foo()    | Foo::Foo()
+// | _Z1fSs        | f()           | f(std::basic_string<char,
+// |               |               |   std::char_traits<char>,
+// |               |               |   std::allocator<char> >)
+//
+// See the unit test for more examples.
+//
+// Note: we might want to write demanglers for ABIs other than Itanium
+// C++ ABI in the future.
+//
+
+#ifndef ABSL_DEBUGGING_INTERNAL_DEMANGLE_H_
+#define ABSL_DEBUGGING_INTERNAL_DEMANGLE_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Demangle `mangled`.  On success, return true and write the
+// demangled symbol name to `out`.  Otherwise, return false.
+// `out` is modified even if demangling is unsuccessful.
+bool Demangle(const char *mangled, char *out, int out_size);
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_DEMANGLE_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/demangle_test.cc b/third_party/abseil_cpp/absl/debugging/internal/demangle_test.cc
new file mode 100644
index 000000000000..c6f1ce184c10
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/demangle_test.cc
@@ -0,0 +1,195 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/debugging/internal/demangle.h"
+
+#include <cstdlib>
+#include <string>
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/debugging/internal/stack_consumption.h"
+#include "absl/memory/memory.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+namespace {
+
+// A wrapper function for Demangle() to make the unit test simple.
+static const char *DemangleIt(const char * const mangled) {
+  static char demangled[4096];
+  if (Demangle(mangled, demangled, sizeof(demangled))) {
+    return demangled;
+  } else {
+    return mangled;
+  }
+}
+
+// Test corner cases of bounary conditions.
+TEST(Demangle, CornerCases) {
+  char tmp[10];
+  EXPECT_TRUE(Demangle("_Z6foobarv", tmp, sizeof(tmp)));
+  // sizeof("foobar()") == 9
+  EXPECT_STREQ("foobar()", tmp);
+  EXPECT_TRUE(Demangle("_Z6foobarv", tmp, 9));
+  EXPECT_STREQ("foobar()", tmp);
+  EXPECT_FALSE(Demangle("_Z6foobarv", tmp, 8));  // Not enough.
+  EXPECT_FALSE(Demangle("_Z6foobarv", tmp, 1));
+  EXPECT_FALSE(Demangle("_Z6foobarv", tmp, 0));
+  EXPECT_FALSE(Demangle("_Z6foobarv", nullptr, 0));  // Should not cause SEGV.
+  EXPECT_FALSE(Demangle("_Z1000000", tmp, 9));
+}
+
+// Test handling of functions suffixed with .clone.N, which is used
+// by GCC 4.5.x (and our locally-modified version of GCC 4.4.x), and
+// .constprop.N and .isra.N, which are used by GCC 4.6.x.  These
+// suffixes are used to indicate functions which have been cloned
+// during optimization.  We ignore these suffixes.
+TEST(Demangle, Clones) {
+  char tmp[20];
+  EXPECT_TRUE(Demangle("_ZL3Foov", tmp, sizeof(tmp)));
+  EXPECT_STREQ("Foo()", tmp);
+  EXPECT_TRUE(Demangle("_ZL3Foov.clone.3", tmp, sizeof(tmp)));
+  EXPECT_STREQ("Foo()", tmp);
+  EXPECT_TRUE(Demangle("_ZL3Foov.constprop.80", tmp, sizeof(tmp)));
+  EXPECT_STREQ("Foo()", tmp);
+  EXPECT_TRUE(Demangle("_ZL3Foov.isra.18", tmp, sizeof(tmp)));
+  EXPECT_STREQ("Foo()", tmp);
+  EXPECT_TRUE(Demangle("_ZL3Foov.isra.2.constprop.18", tmp, sizeof(tmp)));
+  EXPECT_STREQ("Foo()", tmp);
+  // Invalid (truncated), should not demangle.
+  EXPECT_FALSE(Demangle("_ZL3Foov.clo", tmp, sizeof(tmp)));
+  // Invalid (.clone. not followed by number), should not demangle.
+  EXPECT_FALSE(Demangle("_ZL3Foov.clone.", tmp, sizeof(tmp)));
+  // Invalid (.clone. followed by non-number), should not demangle.
+  EXPECT_FALSE(Demangle("_ZL3Foov.clone.foo", tmp, sizeof(tmp)));
+  // Invalid (.constprop. not followed by number), should not demangle.
+  EXPECT_FALSE(Demangle("_ZL3Foov.isra.2.constprop.", tmp, sizeof(tmp)));
+}
+
+// Tests that verify that Demangle footprint is within some limit.
+// They are not to be run under sanitizers as the sanitizers increase
+// stack consumption by about 4x.
+#if defined(ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION) &&   \
+    !defined(ADDRESS_SANITIZER) && !defined(MEMORY_SANITIZER) && \
+    !defined(THREAD_SANITIZER)
+
+static const char *g_mangled;
+static char g_demangle_buffer[4096];
+static char *g_demangle_result;
+
+static void DemangleSignalHandler(int signo) {
+  if (Demangle(g_mangled, g_demangle_buffer, sizeof(g_demangle_buffer))) {
+    g_demangle_result = g_demangle_buffer;
+  } else {
+    g_demangle_result = nullptr;
+  }
+}
+
+// Call Demangle and figure out the stack footprint of this call.
+static const char *DemangleStackConsumption(const char *mangled,
+                                            int *stack_consumed) {
+  g_mangled = mangled;
+  *stack_consumed = GetSignalHandlerStackConsumption(DemangleSignalHandler);
+  ABSL_RAW_LOG(INFO, "Stack consumption of Demangle: %d", *stack_consumed);
+  return g_demangle_result;
+}
+
+// Demangle stack consumption should be within 8kB for simple mangled names
+// with some level of nesting. With alternate signal stack we have 64K,
+// but some signal handlers run on thread stack, and could have arbitrarily
+// little space left (so we don't want to make this number too large).
+const int kStackConsumptionUpperLimit = 8192;
+
+// Returns a mangled name nested to the given depth.
+static std::string NestedMangledName(int depth) {
+  std::string mangled_name = "_Z1a";
+  if (depth > 0) {
+    mangled_name += "IXL";
+    mangled_name += NestedMangledName(depth - 1);
+    mangled_name += "EEE";
+  }
+  return mangled_name;
+}
+
+TEST(Demangle, DemangleStackConsumption) {
+  // Measure stack consumption of Demangle for nested mangled names of varying
+  // depth.  Since Demangle is implemented as a recursive descent parser,
+  // stack consumption will grow as the nesting depth increases.  By measuring
+  // the stack consumption for increasing depths, we can see the growing
+  // impact of any stack-saving changes made to the code for Demangle.
+  int stack_consumed = 0;
+
+  const char *demangled =
+      DemangleStackConsumption("_Z6foobarv", &stack_consumed);
+  EXPECT_STREQ("foobar()", demangled);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, kStackConsumptionUpperLimit);
+
+  const std::string nested_mangled_name0 = NestedMangledName(0);
+  demangled = DemangleStackConsumption(nested_mangled_name0.c_str(),
+                                       &stack_consumed);
+  EXPECT_STREQ("a", demangled);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, kStackConsumptionUpperLimit);
+
+  const std::string nested_mangled_name1 = NestedMangledName(1);
+  demangled = DemangleStackConsumption(nested_mangled_name1.c_str(),
+                                       &stack_consumed);
+  EXPECT_STREQ("a<>", demangled);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, kStackConsumptionUpperLimit);
+
+  const std::string nested_mangled_name2 = NestedMangledName(2);
+  demangled = DemangleStackConsumption(nested_mangled_name2.c_str(),
+                                       &stack_consumed);
+  EXPECT_STREQ("a<>", demangled);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, kStackConsumptionUpperLimit);
+
+  const std::string nested_mangled_name3 = NestedMangledName(3);
+  demangled = DemangleStackConsumption(nested_mangled_name3.c_str(),
+                                       &stack_consumed);
+  EXPECT_STREQ("a<>", demangled);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, kStackConsumptionUpperLimit);
+}
+
+#endif  // Stack consumption tests
+
+static void TestOnInput(const char* input) {
+  static const int kOutSize = 1048576;
+  auto out = absl::make_unique<char[]>(kOutSize);
+  Demangle(input, out.get(), kOutSize);
+}
+
+TEST(DemangleRegression, NegativeLength) {
+  TestOnInput("_ZZn4");
+}
+
+TEST(DemangleRegression, DeeplyNestedArrayType) {
+  const int depth = 100000;
+  std::string data = "_ZStI";
+  data.reserve(data.size() + 3 * depth + 1);
+  for (int i = 0; i < depth; i++) {
+    data += "A1_";
+  }
+  TestOnInput(data.c_str());
+}
+
+}  // namespace
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.cc b/third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.cc
new file mode 100644
index 000000000000..24cc01302dc5
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.cc
@@ -0,0 +1,382 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Allow dynamic symbol lookup in an in-memory Elf image.
+//
+
+#include "absl/debugging/internal/elf_mem_image.h"
+
+#ifdef ABSL_HAVE_ELF_MEM_IMAGE  // defined in elf_mem_image.h
+
+#include <string.h>
+#include <cassert>
+#include <cstddef>
+#include "absl/base/internal/raw_logging.h"
+
+// From binutils/include/elf/common.h (this doesn't appear to be documented
+// anywhere else).
+//
+//   /* This flag appears in a Versym structure.  It means that the symbol
+//      is hidden, and is only visible with an explicit version number.
+//      This is a GNU extension.  */
+//   #define VERSYM_HIDDEN           0x8000
+//
+//   /* This is the mask for the rest of the Versym information.  */
+//   #define VERSYM_VERSION          0x7fff
+
+#define VERSYM_VERSION 0x7fff
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+namespace {
+
+#if __WORDSIZE == 32
+const int kElfClass = ELFCLASS32;
+int ElfBind(const ElfW(Sym) *symbol) { return ELF32_ST_BIND(symbol->st_info); }
+int ElfType(const ElfW(Sym) *symbol) { return ELF32_ST_TYPE(symbol->st_info); }
+#elif __WORDSIZE == 64
+const int kElfClass = ELFCLASS64;
+int ElfBind(const ElfW(Sym) *symbol) { return ELF64_ST_BIND(symbol->st_info); }
+int ElfType(const ElfW(Sym) *symbol) { return ELF64_ST_TYPE(symbol->st_info); }
+#else
+const int kElfClass = -1;
+int ElfBind(const ElfW(Sym) *) {
+  ABSL_RAW_LOG(FATAL, "Unexpected word size");
+  return 0;
+}
+int ElfType(const ElfW(Sym) *) {
+  ABSL_RAW_LOG(FATAL, "Unexpected word size");
+  return 0;
+}
+#endif
+
+// Extract an element from one of the ELF tables, cast it to desired type.
+// This is just a simple arithmetic and a glorified cast.
+// Callers are responsible for bounds checking.
+template <typename T>
+const T *GetTableElement(const ElfW(Ehdr) * ehdr, ElfW(Off) table_offset,
+                         ElfW(Word) element_size, size_t index) {
+  return reinterpret_cast<const T*>(reinterpret_cast<const char *>(ehdr)
+                                    + table_offset
+                                    + index * element_size);
+}
+
+}  // namespace
+
+// The value of this variable doesn't matter; it's used only for its
+// unique address.
+const int ElfMemImage::kInvalidBaseSentinel = 0;
+
+ElfMemImage::ElfMemImage(const void *base) {
+  ABSL_RAW_CHECK(base != kInvalidBase, "bad pointer");
+  Init(base);
+}
+
+int ElfMemImage::GetNumSymbols() const {
+  if (!hash_) {
+    return 0;
+  }
+  // See http://www.caldera.com/developers/gabi/latest/ch5.dynamic.html#hash
+  return hash_[1];
+}
+
+const ElfW(Sym) *ElfMemImage::GetDynsym(int index) const {
+  ABSL_RAW_CHECK(index < GetNumSymbols(), "index out of range");
+  return dynsym_ + index;
+}
+
+const ElfW(Versym) *ElfMemImage::GetVersym(int index) const {
+  ABSL_RAW_CHECK(index < GetNumSymbols(), "index out of range");
+  return versym_ + index;
+}
+
+const ElfW(Phdr) *ElfMemImage::GetPhdr(int index) const {
+  ABSL_RAW_CHECK(index < ehdr_->e_phnum, "index out of range");
+  return GetTableElement<ElfW(Phdr)>(ehdr_,
+                                     ehdr_->e_phoff,
+                                     ehdr_->e_phentsize,
+                                     index);
+}
+
+const char *ElfMemImage::GetDynstr(ElfW(Word) offset) const {
+  ABSL_RAW_CHECK(offset < strsize_, "offset out of range");
+  return dynstr_ + offset;
+}
+
+const void *ElfMemImage::GetSymAddr(const ElfW(Sym) *sym) const {
+  if (sym->st_shndx == SHN_UNDEF || sym->st_shndx >= SHN_LORESERVE) {
+    // Symbol corresponds to "special" (e.g. SHN_ABS) section.
+    return reinterpret_cast<const void *>(sym->st_value);
+  }
+  ABSL_RAW_CHECK(link_base_ < sym->st_value, "symbol out of range");
+  return GetTableElement<char>(ehdr_, 0, 1, sym->st_value - link_base_);
+}
+
+const ElfW(Verdef) *ElfMemImage::GetVerdef(int index) const {
+  ABSL_RAW_CHECK(0 <= index && static_cast<size_t>(index) <= verdefnum_,
+                 "index out of range");
+  const ElfW(Verdef) *version_definition = verdef_;
+  while (version_definition->vd_ndx < index && version_definition->vd_next) {
+    const char *const version_definition_as_char =
+        reinterpret_cast<const char *>(version_definition);
+    version_definition =
+        reinterpret_cast<const ElfW(Verdef) *>(version_definition_as_char +
+                                               version_definition->vd_next);
+  }
+  return version_definition->vd_ndx == index ? version_definition : nullptr;
+}
+
+const ElfW(Verdaux) *ElfMemImage::GetVerdefAux(
+    const ElfW(Verdef) *verdef) const {
+  return reinterpret_cast<const ElfW(Verdaux) *>(verdef+1);
+}
+
+const char *ElfMemImage::GetVerstr(ElfW(Word) offset) const {
+  ABSL_RAW_CHECK(offset < strsize_, "offset out of range");
+  return dynstr_ + offset;
+}
+
+void ElfMemImage::Init(const void *base) {
+  ehdr_      = nullptr;
+  dynsym_    = nullptr;
+  dynstr_    = nullptr;
+  versym_    = nullptr;
+  verdef_    = nullptr;
+  hash_      = nullptr;
+  strsize_   = 0;
+  verdefnum_ = 0;
+  link_base_ = ~0L;  // Sentinel: PT_LOAD .p_vaddr can't possibly be this.
+  if (!base) {
+    return;
+  }
+  const char *const base_as_char = reinterpret_cast<const char *>(base);
+  if (base_as_char[EI_MAG0] != ELFMAG0 || base_as_char[EI_MAG1] != ELFMAG1 ||
+      base_as_char[EI_MAG2] != ELFMAG2 || base_as_char[EI_MAG3] != ELFMAG3) {
+    assert(false);
+    return;
+  }
+  int elf_class = base_as_char[EI_CLASS];
+  if (elf_class != kElfClass) {
+    assert(false);
+    return;
+  }
+  switch (base_as_char[EI_DATA]) {
+    case ELFDATA2LSB: {
+      if (__LITTLE_ENDIAN != __BYTE_ORDER) {
+        assert(false);
+        return;
+      }
+      break;
+    }
+    case ELFDATA2MSB: {
+      if (__BIG_ENDIAN != __BYTE_ORDER) {
+        assert(false);
+        return;
+      }
+      break;
+    }
+    default: {
+      assert(false);
+      return;
+    }
+  }
+
+  ehdr_ = reinterpret_cast<const ElfW(Ehdr) *>(base);
+  const ElfW(Phdr) *dynamic_program_header = nullptr;
+  for (int i = 0; i < ehdr_->e_phnum; ++i) {
+    const ElfW(Phdr) *const program_header = GetPhdr(i);
+    switch (program_header->p_type) {
+      case PT_LOAD:
+        if (!~link_base_) {
+          link_base_ = program_header->p_vaddr;
+        }
+        break;
+      case PT_DYNAMIC:
+        dynamic_program_header = program_header;
+        break;
+    }
+  }
+  if (!~link_base_ || !dynamic_program_header) {
+    assert(false);
+    // Mark this image as not present. Can not recur infinitely.
+    Init(nullptr);
+    return;
+  }
+  ptrdiff_t relocation =
+      base_as_char - reinterpret_cast<const char *>(link_base_);
+  ElfW(Dyn) *dynamic_entry =
+      reinterpret_cast<ElfW(Dyn) *>(dynamic_program_header->p_vaddr +
+                                    relocation);
+  for (; dynamic_entry->d_tag != DT_NULL; ++dynamic_entry) {
+    const ElfW(Xword) value = dynamic_entry->d_un.d_val + relocation;
+    switch (dynamic_entry->d_tag) {
+      case DT_HASH:
+        hash_ = reinterpret_cast<ElfW(Word) *>(value);
+        break;
+      case DT_SYMTAB:
+        dynsym_ = reinterpret_cast<ElfW(Sym) *>(value);
+        break;
+      case DT_STRTAB:
+        dynstr_ = reinterpret_cast<const char *>(value);
+        break;
+      case DT_VERSYM:
+        versym_ = reinterpret_cast<ElfW(Versym) *>(value);
+        break;
+      case DT_VERDEF:
+        verdef_ = reinterpret_cast<ElfW(Verdef) *>(value);
+        break;
+      case DT_VERDEFNUM:
+        verdefnum_ = dynamic_entry->d_un.d_val;
+        break;
+      case DT_STRSZ:
+        strsize_ = dynamic_entry->d_un.d_val;
+        break;
+      default:
+        // Unrecognized entries explicitly ignored.
+        break;
+    }
+  }
+  if (!hash_ || !dynsym_ || !dynstr_ || !versym_ ||
+      !verdef_ || !verdefnum_ || !strsize_) {
+    assert(false);  // invalid VDSO
+    // Mark this image as not present. Can not recur infinitely.
+    Init(nullptr);
+    return;
+  }
+}
+
+bool ElfMemImage::LookupSymbol(const char *name,
+                               const char *version,
+                               int type,
+                               SymbolInfo *info_out) const {
+  for (const SymbolInfo& info : *this) {
+    if (strcmp(info.name, name) == 0 && strcmp(info.version, version) == 0 &&
+        ElfType(info.symbol) == type) {
+      if (info_out) {
+        *info_out = info;
+      }
+      return true;
+    }
+  }
+  return false;
+}
+
+bool ElfMemImage::LookupSymbolByAddress(const void *address,
+                                        SymbolInfo *info_out) const {
+  for (const SymbolInfo& info : *this) {
+    const char *const symbol_start =
+        reinterpret_cast<const char *>(info.address);
+    const char *const symbol_end = symbol_start + info.symbol->st_size;
+    if (symbol_start <= address && address < symbol_end) {
+      if (info_out) {
+        // Client wants to know details for that symbol (the usual case).
+        if (ElfBind(info.symbol) == STB_GLOBAL) {
+          // Strong symbol; just return it.
+          *info_out = info;
+          return true;
+        } else {
+          // Weak or local. Record it, but keep looking for a strong one.
+          *info_out = info;
+        }
+      } else {
+        // Client only cares if there is an overlapping symbol.
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+ElfMemImage::SymbolIterator::SymbolIterator(const void *const image, int index)
+    : index_(index), image_(image) {
+}
+
+const ElfMemImage::SymbolInfo *ElfMemImage::SymbolIterator::operator->() const {
+  return &info_;
+}
+
+const ElfMemImage::SymbolInfo& ElfMemImage::SymbolIterator::operator*() const {
+  return info_;
+}
+
+bool ElfMemImage::SymbolIterator::operator==(const SymbolIterator &rhs) const {
+  return this->image_ == rhs.image_ && this->index_ == rhs.index_;
+}
+
+bool ElfMemImage::SymbolIterator::operator!=(const SymbolIterator &rhs) const {
+  return !(*this == rhs);
+}
+
+ElfMemImage::SymbolIterator &ElfMemImage::SymbolIterator::operator++() {
+  this->Update(1);
+  return *this;
+}
+
+ElfMemImage::SymbolIterator ElfMemImage::begin() const {
+  SymbolIterator it(this, 0);
+  it.Update(0);
+  return it;
+}
+
+ElfMemImage::SymbolIterator ElfMemImage::end() const {
+  return SymbolIterator(this, GetNumSymbols());
+}
+
+void ElfMemImage::SymbolIterator::Update(int increment) {
+  const ElfMemImage *image = reinterpret_cast<const ElfMemImage *>(image_);
+  ABSL_RAW_CHECK(image->IsPresent() || increment == 0, "");
+  if (!image->IsPresent()) {
+    return;
+  }
+  index_ += increment;
+  if (index_ >= image->GetNumSymbols()) {
+    index_ = image->GetNumSymbols();
+    return;
+  }
+  const ElfW(Sym)    *symbol = image->GetDynsym(index_);
+  const ElfW(Versym) *version_symbol = image->GetVersym(index_);
+  ABSL_RAW_CHECK(symbol && version_symbol, "");
+  const char *const symbol_name = image->GetDynstr(symbol->st_name);
+  const ElfW(Versym) version_index = version_symbol[0] & VERSYM_VERSION;
+  const ElfW(Verdef) *version_definition = nullptr;
+  const char *version_name = "";
+  if (symbol->st_shndx == SHN_UNDEF) {
+    // Undefined symbols reference DT_VERNEED, not DT_VERDEF, and
+    // version_index could well be greater than verdefnum_, so calling
+    // GetVerdef(version_index) may trigger assertion.
+  } else {
+    version_definition = image->GetVerdef(version_index);
+  }
+  if (version_definition) {
+    // I am expecting 1 or 2 auxiliary entries: 1 for the version itself,
+    // optional 2nd if the version has a parent.
+    ABSL_RAW_CHECK(
+        version_definition->vd_cnt == 1 || version_definition->vd_cnt == 2,
+        "wrong number of entries");
+    const ElfW(Verdaux) *version_aux = image->GetVerdefAux(version_definition);
+    version_name = image->GetVerstr(version_aux->vda_name);
+  }
+  info_.name    = symbol_name;
+  info_.version = version_name;
+  info_.address = image->GetSymAddr(symbol);
+  info_.symbol  = symbol;
+}
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_HAVE_ELF_MEM_IMAGE
diff --git a/third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.h b/third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.h
new file mode 100644
index 000000000000..46bfade3503e
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/elf_mem_image.h
@@ -0,0 +1,134 @@
+/*
+ * Copyright 2017 The Abseil Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Allow dynamic symbol lookup for in-memory Elf images.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
+#define ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
+
+// Including this will define the __GLIBC__ macro if glibc is being
+// used.
+#include <climits>
+
+#include "absl/base/config.h"
+
+// Maybe one day we can rewrite this file not to require the elf
+// symbol extensions in glibc, but for right now we need them.
+#ifdef ABSL_HAVE_ELF_MEM_IMAGE
+#error ABSL_HAVE_ELF_MEM_IMAGE cannot be directly set
+#endif
+
+#if defined(__ELF__) && defined(__GLIBC__) && !defined(__native_client__) && \
+    !defined(__asmjs__) && !defined(__wasm__)
+#define ABSL_HAVE_ELF_MEM_IMAGE 1
+#endif
+
+#ifdef ABSL_HAVE_ELF_MEM_IMAGE
+
+#include <link.h>  // for ElfW
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// An in-memory ELF image (may not exist on disk).
+class ElfMemImage {
+ private:
+  // Sentinel: there could never be an elf image at &kInvalidBaseSentinel.
+  static const int kInvalidBaseSentinel;
+
+ public:
+  // Sentinel: there could never be an elf image at this address.
+  static constexpr const void *const kInvalidBase =
+    static_cast<const void*>(&kInvalidBaseSentinel);
+
+  // Information about a single vdso symbol.
+  // All pointers are into .dynsym, .dynstr, or .text of the VDSO.
+  // Do not free() them or modify through them.
+  struct SymbolInfo {
+    const char      *name;      // E.g. "__vdso_getcpu"
+    const char      *version;   // E.g. "LINUX_2.6", could be ""
+                                // for unversioned symbol.
+    const void      *address;   // Relocated symbol address.
+    const ElfW(Sym) *symbol;    // Symbol in the dynamic symbol table.
+  };
+
+  // Supports iteration over all dynamic symbols.
+  class SymbolIterator {
+   public:
+    friend class ElfMemImage;
+    const SymbolInfo *operator->() const;
+    const SymbolInfo &operator*() const;
+    SymbolIterator& operator++();
+    bool operator!=(const SymbolIterator &rhs) const;
+    bool operator==(const SymbolIterator &rhs) const;
+   private:
+    SymbolIterator(const void *const image, int index);
+    void Update(int incr);
+    SymbolInfo info_;
+    int index_;
+    const void *const image_;
+  };
+
+
+  explicit ElfMemImage(const void *base);
+  void                 Init(const void *base);
+  bool                 IsPresent() const { return ehdr_ != nullptr; }
+  const ElfW(Phdr)*    GetPhdr(int index) const;
+  const ElfW(Sym)*     GetDynsym(int index) const;
+  const ElfW(Versym)*  GetVersym(int index) const;
+  const ElfW(Verdef)*  GetVerdef(int index) const;
+  const ElfW(Verdaux)* GetVerdefAux(const ElfW(Verdef) *verdef) const;
+  const char*          GetDynstr(ElfW(Word) offset) const;
+  const void*          GetSymAddr(const ElfW(Sym) *sym) const;
+  const char*          GetVerstr(ElfW(Word) offset) const;
+  int                  GetNumSymbols() const;
+
+  SymbolIterator begin() const;
+  SymbolIterator end() const;
+
+  // Look up versioned dynamic symbol in the image.
+  // Returns false if image is not present, or doesn't contain given
+  // symbol/version/type combination.
+  // If info_out is non-null, additional details are filled in.
+  bool LookupSymbol(const char *name, const char *version,
+                    int symbol_type, SymbolInfo *info_out) const;
+
+  // Find info about symbol (if any) which overlaps given address.
+  // Returns true if symbol was found; false if image isn't present
+  // or doesn't have a symbol overlapping given address.
+  // If info_out is non-null, additional details are filled in.
+  bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
+
+ private:
+  const ElfW(Ehdr) *ehdr_;
+  const ElfW(Sym) *dynsym_;
+  const ElfW(Versym) *versym_;
+  const ElfW(Verdef) *verdef_;
+  const ElfW(Word) *hash_;
+  const char *dynstr_;
+  size_t strsize_;
+  size_t verdefnum_;
+  ElfW(Addr) link_base_;     // Link-time base (p_vaddr of first PT_LOAD).
+};
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_HAVE_ELF_MEM_IMAGE
+
+#endif  // ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/examine_stack.cc b/third_party/abseil_cpp/absl/debugging/internal/examine_stack.cc
new file mode 100644
index 000000000000..a3dd893a9dfe
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/examine_stack.cc
@@ -0,0 +1,157 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "absl/debugging/internal/examine_stack.h"
+
+#ifndef _WIN32
+#include <unistd.h>
+#endif
+
+#include <csignal>
+#include <cstdio>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/macros.h"
+#include "absl/debugging/stacktrace.h"
+#include "absl/debugging/symbolize.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Returns the program counter from signal context, nullptr if
+// unknown. vuc is a ucontext_t*. We use void* to avoid the use of
+// ucontext_t on non-POSIX systems.
+void* GetProgramCounter(void* vuc) {
+#ifdef __linux__
+  if (vuc != nullptr) {
+    ucontext_t* context = reinterpret_cast<ucontext_t*>(vuc);
+#if defined(__aarch64__)
+    return reinterpret_cast<void*>(context->uc_mcontext.pc);
+#elif defined(__arm__)
+    return reinterpret_cast<void*>(context->uc_mcontext.arm_pc);
+#elif defined(__i386__)
+    if (14 < ABSL_ARRAYSIZE(context->uc_mcontext.gregs))
+      return reinterpret_cast<void*>(context->uc_mcontext.gregs[14]);
+#elif defined(__mips__)
+    return reinterpret_cast<void*>(context->uc_mcontext.pc);
+#elif defined(__powerpc64__)
+    return reinterpret_cast<void*>(context->uc_mcontext.gp_regs[32]);
+#elif defined(__powerpc__)
+    return reinterpret_cast<void*>(context->uc_mcontext.regs->nip);
+#elif defined(__riscv)
+    return reinterpret_cast<void*>(context->uc_mcontext.__gregs[REG_PC]);
+#elif defined(__s390__) && !defined(__s390x__)
+    return reinterpret_cast<void*>(context->uc_mcontext.psw.addr & 0x7fffffff);
+#elif defined(__s390__) && defined(__s390x__)
+    return reinterpret_cast<void*>(context->uc_mcontext.psw.addr);
+#elif defined(__x86_64__)
+    if (16 < ABSL_ARRAYSIZE(context->uc_mcontext.gregs))
+      return reinterpret_cast<void*>(context->uc_mcontext.gregs[16]);
+#else
+#error "Undefined Architecture."
+#endif
+  }
+#elif defined(__akaros__)
+  auto* ctx = reinterpret_cast<struct user_context*>(vuc);
+  return reinterpret_cast<void*>(get_user_ctx_pc(ctx));
+#endif
+  static_cast<void>(vuc);
+  return nullptr;
+}
+
+// The %p field width for printf() functions is two characters per byte,
+// and two extra for the leading "0x".
+static constexpr int kPrintfPointerFieldWidth = 2 + 2 * sizeof(void*);
+
+// Print a program counter, its stack frame size, and its symbol name.
+// Note that there is a separate symbolize_pc argument. Return addresses may be
+// at the end of the function, and this allows the caller to back up from pc if
+// appropriate.
+static void DumpPCAndFrameSizeAndSymbol(void (*writerfn)(const char*, void*),
+                                        void* writerfn_arg, void* pc,
+                                        void* symbolize_pc, int framesize,
+                                        const char* const prefix) {
+  char tmp[1024];
+  const char* symbol = "(unknown)";
+  if (absl::Symbolize(symbolize_pc, tmp, sizeof(tmp))) {
+    symbol = tmp;
+  }
+  char buf[1024];
+  if (framesize <= 0) {
+    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)  %s\n", prefix,
+             kPrintfPointerFieldWidth, pc, symbol);
+  } else {
+    snprintf(buf, sizeof(buf), "%s@ %*p  %9d  %s\n", prefix,
+             kPrintfPointerFieldWidth, pc, framesize, symbol);
+  }
+  writerfn(buf, writerfn_arg);
+}
+
+// Print a program counter and the corresponding stack frame size.
+static void DumpPCAndFrameSize(void (*writerfn)(const char*, void*),
+                               void* writerfn_arg, void* pc, int framesize,
+                               const char* const prefix) {
+  char buf[100];
+  if (framesize <= 0) {
+    snprintf(buf, sizeof(buf), "%s@ %*p  (unknown)\n", prefix,
+             kPrintfPointerFieldWidth, pc);
+  } else {
+    snprintf(buf, sizeof(buf), "%s@ %*p  %9d\n", prefix,
+             kPrintfPointerFieldWidth, pc, framesize);
+  }
+  writerfn(buf, writerfn_arg);
+}
+
+void DumpPCAndFrameSizesAndStackTrace(
+    void* pc, void* const stack[], int frame_sizes[], int depth,
+    int min_dropped_frames, bool symbolize_stacktrace,
+    void (*writerfn)(const char*, void*), void* writerfn_arg) {
+  if (pc != nullptr) {
+    // We don't know the stack frame size for PC, use 0.
+    if (symbolize_stacktrace) {
+      DumpPCAndFrameSizeAndSymbol(writerfn, writerfn_arg, pc, pc, 0, "PC: ");
+    } else {
+      DumpPCAndFrameSize(writerfn, writerfn_arg, pc, 0, "PC: ");
+    }
+  }
+  for (int i = 0; i < depth; i++) {
+    if (symbolize_stacktrace) {
+      // Pass the previous address of pc as the symbol address because pc is a
+      // return address, and an overrun may occur when the function ends with a
+      // call to a function annotated noreturn (e.g. CHECK). Note that we don't
+      // do this for pc above, as the adjustment is only correct for return
+      // addresses.
+      DumpPCAndFrameSizeAndSymbol(writerfn, writerfn_arg, stack[i],
+                                  reinterpret_cast<char*>(stack[i]) - 1,
+                                  frame_sizes[i], "    ");
+    } else {
+      DumpPCAndFrameSize(writerfn, writerfn_arg, stack[i], frame_sizes[i],
+                         "    ");
+    }
+  }
+  if (min_dropped_frames > 0) {
+    char buf[100];
+    snprintf(buf, sizeof(buf), "    @ ... and at least %d more frames\n",
+             min_dropped_frames);
+    writerfn(buf, writerfn_arg);
+  }
+}
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/internal/examine_stack.h b/third_party/abseil_cpp/absl/debugging/internal/examine_stack.h
new file mode 100644
index 000000000000..393369131f1e
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/examine_stack.h
@@ -0,0 +1,42 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_DEBUGGING_INTERNAL_EXAMINE_STACK_H_
+#define ABSL_DEBUGGING_INTERNAL_EXAMINE_STACK_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Returns the program counter from signal context, or nullptr if
+// unknown. `vuc` is a ucontext_t*. We use void* to avoid the use of
+// ucontext_t on non-POSIX systems.
+void* GetProgramCounter(void* vuc);
+
+// Uses `writerfn` to dump the program counter, stack trace, and stack
+// frame sizes.
+void DumpPCAndFrameSizesAndStackTrace(
+    void* pc, void* const stack[], int frame_sizes[], int depth,
+    int min_dropped_frames, bool symbolize_stacktrace,
+    void (*writerfn)(const char*, void*), void* writerfn_arg);
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_EXAMINE_STACK_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stack_consumption.cc b/third_party/abseil_cpp/absl/debugging/internal/stack_consumption.cc
new file mode 100644
index 000000000000..875ca6d91f7f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stack_consumption.cc
@@ -0,0 +1,184 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/debugging/internal/stack_consumption.h"
+
+#ifdef ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
+
+#include <signal.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include <string.h>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+namespace {
+
+// This code requires that we know the direction in which the stack
+// grows. It is commonly believed that this can be detected by putting
+// a variable on the stack and then passing its address to a function
+// that compares the address of this variable to the address of a
+// variable on the function's own stack. However, this is unspecified
+// behavior in C++: If two pointers p and q of the same type point to
+// different objects that are not members of the same object or
+// elements of the same array or to different functions, or if only
+// one of them is null, the results of p<q, p>q, p<=q, and p>=q are
+// unspecified. Therefore, instead we hardcode the direction of the
+// stack on platforms we know about.
+#if defined(__i386__) || defined(__x86_64__) || defined(__ppc__)
+constexpr bool kStackGrowsDown = true;
+#else
+#error Need to define kStackGrowsDown
+#endif
+
+// To measure the stack footprint of some code, we create a signal handler
+// (for SIGUSR2 say) that exercises this code on an alternate stack. This
+// alternate stack is initialized to some known pattern (0x55, 0x55, 0x55,
+// ...). We then self-send this signal, and after the signal handler returns,
+// look at the alternate stack buffer to see what portion has been touched.
+//
+// This trick gives us the the stack footprint of the signal handler.  But the
+// signal handler, even before the code for it is exercised, consumes some
+// stack already. We however only want the stack usage of the code inside the
+// signal handler. To measure this accurately, we install two signal handlers:
+// one that does nothing and just returns, and the user-provided signal
+// handler. The difference between the stack consumption of these two signals
+// handlers should give us the stack foorprint of interest.
+
+void EmptySignalHandler(int) {}
+
+// This is arbitrary value, and could be increase further, at the cost of
+// memset()ting it all to known sentinel value.
+constexpr int kAlternateStackSize = 64 << 10;  // 64KiB
+
+constexpr int kSafetyMargin = 32;
+constexpr char kAlternateStackFillValue = 0x55;
+
+// These helper functions look at the alternate stack buffer, and figure
+// out what portion of this buffer has been touched - this is the stack
+// consumption of the signal handler running on this alternate stack.
+// This function will return -1 if the alternate stack buffer has not been
+// touched. It will abort the program if the buffer has overflowed or is about
+// to overflow.
+int GetStackConsumption(const void* const altstack) {
+  const char* begin;
+  int increment;
+  if (kStackGrowsDown) {
+    begin = reinterpret_cast<const char*>(altstack);
+    increment = 1;
+  } else {
+    begin = reinterpret_cast<const char*>(altstack) + kAlternateStackSize - 1;
+    increment = -1;
+  }
+
+  for (int usage_count = kAlternateStackSize; usage_count > 0; --usage_count) {
+    if (*begin != kAlternateStackFillValue) {
+      ABSL_RAW_CHECK(usage_count <= kAlternateStackSize - kSafetyMargin,
+                     "Buffer has overflowed or is about to overflow");
+      return usage_count;
+    }
+    begin += increment;
+  }
+
+  ABSL_RAW_LOG(FATAL, "Unreachable code");
+  return -1;
+}
+
+}  // namespace
+
+int GetSignalHandlerStackConsumption(void (*signal_handler)(int)) {
+  // The alt-signal-stack cannot be heap allocated because there is a
+  // bug in glibc-2.2 where some signal handler setup code looks at the
+  // current stack pointer to figure out what thread is currently running.
+  // Therefore, the alternate stack must be allocated from the main stack
+  // itself.
+  void* altstack = mmap(nullptr, kAlternateStackSize, PROT_READ | PROT_WRITE,
+                        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  ABSL_RAW_CHECK(altstack != MAP_FAILED, "mmap() failed");
+
+  // Set up the alt-signal-stack (and save the older one).
+  stack_t sigstk;
+  memset(&sigstk, 0, sizeof(sigstk));
+  sigstk.ss_sp = altstack;
+  sigstk.ss_size = kAlternateStackSize;
+  sigstk.ss_flags = 0;
+  stack_t old_sigstk;
+  memset(&old_sigstk, 0, sizeof(old_sigstk));
+  ABSL_RAW_CHECK(sigaltstack(&sigstk, &old_sigstk) == 0,
+                 "sigaltstack() failed");
+
+  // Set up SIGUSR1 and SIGUSR2 signal handlers (and save the older ones).
+  struct sigaction sa;
+  memset(&sa, 0, sizeof(sa));
+  struct sigaction old_sa1, old_sa2;
+  sigemptyset(&sa.sa_mask);
+  sa.sa_flags = SA_ONSTACK;
+
+  // SIGUSR1 maps to EmptySignalHandler.
+  sa.sa_handler = EmptySignalHandler;
+  ABSL_RAW_CHECK(sigaction(SIGUSR1, &sa, &old_sa1) == 0, "sigaction() failed");
+
+  // SIGUSR2 maps to signal_handler.
+  sa.sa_handler = signal_handler;
+  ABSL_RAW_CHECK(sigaction(SIGUSR2, &sa, &old_sa2) == 0, "sigaction() failed");
+
+  // Send SIGUSR1 signal and measure the stack consumption of the empty
+  // signal handler.
+  // The first signal might use more stack space. Run once and ignore the
+  // results to get that out of the way.
+  ABSL_RAW_CHECK(kill(getpid(), SIGUSR1) == 0, "kill() failed");
+
+  memset(altstack, kAlternateStackFillValue, kAlternateStackSize);
+  ABSL_RAW_CHECK(kill(getpid(), SIGUSR1) == 0, "kill() failed");
+  int base_stack_consumption = GetStackConsumption(altstack);
+
+  // Send SIGUSR2 signal and measure the stack consumption of signal_handler.
+  ABSL_RAW_CHECK(kill(getpid(), SIGUSR2) == 0, "kill() failed");
+  int signal_handler_stack_consumption = GetStackConsumption(altstack);
+
+  // Now restore the old alt-signal-stack and signal handlers.
+  if (old_sigstk.ss_sp == nullptr && old_sigstk.ss_size == 0 &&
+      (old_sigstk.ss_flags & SS_DISABLE)) {
+    // https://git.musl-libc.org/cgit/musl/commit/src/signal/sigaltstack.c?id=7829f42a2c8944555439380498ab8b924d0f2070
+    // The original stack has ss_size==0 and ss_flags==SS_DISABLE, but some
+    // versions of musl have a bug that rejects ss_size==0. Work around this by
+    // setting ss_size to MINSIGSTKSZ, which should be ignored by the kernel
+    // when SS_DISABLE is set.
+    old_sigstk.ss_size = MINSIGSTKSZ;
+  }
+  ABSL_RAW_CHECK(sigaltstack(&old_sigstk, nullptr) == 0,
+                 "sigaltstack() failed");
+  ABSL_RAW_CHECK(sigaction(SIGUSR1, &old_sa1, nullptr) == 0,
+                 "sigaction() failed");
+  ABSL_RAW_CHECK(sigaction(SIGUSR2, &old_sa2, nullptr) == 0,
+                 "sigaction() failed");
+
+  ABSL_RAW_CHECK(munmap(altstack, kAlternateStackSize) == 0, "munmap() failed");
+  if (signal_handler_stack_consumption != -1 && base_stack_consumption != -1) {
+    return signal_handler_stack_consumption - base_stack_consumption;
+  }
+  return -1;
+}
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stack_consumption.h b/third_party/abseil_cpp/absl/debugging/internal/stack_consumption.h
new file mode 100644
index 000000000000..5e60ec422916
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stack_consumption.h
@@ -0,0 +1,49 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Helper function for measuring stack consumption of signal handlers.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACK_CONSUMPTION_H_
+#define ABSL_DEBUGGING_INTERNAL_STACK_CONSUMPTION_H_
+
+#include "absl/base/config.h"
+
+// The code in this module is not portable.
+// Use this feature test macro to detect its availability.
+#ifdef ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
+#error ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION cannot be set directly
+#elif !defined(__APPLE__) && !defined(_WIN32) && \
+    (defined(__i386__) || defined(__x86_64__) || defined(__ppc__))
+#define ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION 1
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Returns the stack consumption in bytes for the code exercised by
+// signal_handler.  To measure stack consumption, signal_handler is registered
+// as a signal handler, so the code that it exercises must be async-signal
+// safe.  The argument of signal_handler is an implementation detail of signal
+// handlers and should ignored by the code for signal_handler.  Use global
+// variables to pass information between your test code and signal_handler.
+int GetSignalHandlerStackConsumption(void (*signal_handler)(int));
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACK_CONSUMPTION_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stack_consumption_test.cc b/third_party/abseil_cpp/absl/debugging/internal/stack_consumption_test.cc
new file mode 100644
index 000000000000..80445bf43aab
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stack_consumption_test.cc
@@ -0,0 +1,50 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/debugging/internal/stack_consumption.h"
+
+#ifdef ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
+
+#include <string.h>
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+namespace {
+
+static void SimpleSignalHandler(int signo) {
+  char buf[100];
+  memset(buf, 'a', sizeof(buf));
+
+  // Never true, but prevents compiler from optimizing buf out.
+  if (signo == 0) {
+    ABSL_RAW_LOG(INFO, "%p", static_cast<void*>(buf));
+  }
+}
+
+TEST(SignalHandlerStackConsumptionTest, MeasuresStackConsumption) {
+  // Our handler should consume reasonable number of bytes.
+  EXPECT_GE(GetSignalHandlerStackConsumption(SimpleSignalHandler), 100);
+}
+
+}  // namespace
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_aarch64-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_aarch64-inl.inc
new file mode 100644
index 000000000000..14a76f1eb5b3
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_aarch64-inl.inc
@@ -0,0 +1,196 @@
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_AARCH64_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_AARCH64_INL_H_
+
+// Generate stack tracer for aarch64
+
+#if defined(__linux__)
+#include <sys/mman.h>
+#include <ucontext.h>
+#include <unistd.h>
+#endif
+
+#include <atomic>
+#include <cassert>
+#include <cstdint>
+#include <iostream>
+
+#include "absl/base/attributes.h"
+#include "absl/debugging/internal/address_is_readable.h"
+#include "absl/debugging/internal/vdso_support.h"  // a no-op on non-elf or non-glibc systems
+#include "absl/debugging/stacktrace.h"
+
+static const uintptr_t kUnknownFrameSize = 0;
+
+#if defined(__linux__)
+// Returns the address of the VDSO __kernel_rt_sigreturn function, if present.
+static const unsigned char* GetKernelRtSigreturnAddress() {
+  constexpr uintptr_t kImpossibleAddress = 1;
+  ABSL_CONST_INIT static std::atomic<uintptr_t> memoized{kImpossibleAddress};
+  uintptr_t address = memoized.load(std::memory_order_relaxed);
+  if (address != kImpossibleAddress) {
+    return reinterpret_cast<const unsigned char*>(address);
+  }
+
+  address = reinterpret_cast<uintptr_t>(nullptr);
+
+#ifdef ABSL_HAVE_VDSO_SUPPORT
+  absl::debugging_internal::VDSOSupport vdso;
+  if (vdso.IsPresent()) {
+    absl::debugging_internal::VDSOSupport::SymbolInfo symbol_info;
+    if (!vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_2.6.39", STT_FUNC,
+                           &symbol_info) ||
+        symbol_info.address == nullptr) {
+      // Unexpected: VDSO is present, yet the expected symbol is missing
+      // or null.
+      assert(false && "VDSO is present, but doesn't have expected symbol");
+    } else {
+      if (reinterpret_cast<uintptr_t>(symbol_info.address) !=
+          kImpossibleAddress) {
+        address = reinterpret_cast<uintptr_t>(symbol_info.address);
+      } else {
+        assert(false && "VDSO returned invalid address");
+      }
+    }
+  }
+#endif
+
+  memoized.store(address, std::memory_order_relaxed);
+  return reinterpret_cast<const unsigned char*>(address);
+}
+#endif  // __linux__
+
+// Compute the size of a stack frame in [low..high).  We assume that
+// low < high.  Return size of kUnknownFrameSize.
+template<typename T>
+static inline uintptr_t ComputeStackFrameSize(const T* low,
+                                              const T* high) {
+  const char* low_char_ptr = reinterpret_cast<const char *>(low);
+  const char* high_char_ptr = reinterpret_cast<const char *>(high);
+  return low < high ? high_char_ptr - low_char_ptr : kUnknownFrameSize;
+}
+
+// Given a pointer to a stack frame, locate and return the calling
+// stackframe, or return null if no stackframe can be found. Perform sanity
+// checks (the strictness of which is controlled by the boolean parameter
+// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
+template<bool STRICT_UNWINDING, bool WITH_CONTEXT>
+ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
+static void **NextStackFrame(void **old_frame_pointer, const void *uc) {
+  void **new_frame_pointer = reinterpret_cast<void**>(*old_frame_pointer);
+  bool check_frame_size = true;
+
+#if defined(__linux__)
+  if (WITH_CONTEXT && uc != nullptr) {
+    // Check to see if next frame's return address is __kernel_rt_sigreturn.
+    if (old_frame_pointer[1] == GetKernelRtSigreturnAddress()) {
+      const ucontext_t *ucv = static_cast<const ucontext_t *>(uc);
+      // old_frame_pointer[0] is not suitable for unwinding, look at
+      // ucontext to discover frame pointer before signal.
+      void **const pre_signal_frame_pointer =
+          reinterpret_cast<void **>(ucv->uc_mcontext.regs[29]);
+
+      // Check that alleged frame pointer is actually readable. This is to
+      // prevent "double fault" in case we hit the first fault due to e.g.
+      // stack corruption.
+      if (!absl::debugging_internal::AddressIsReadable(
+              pre_signal_frame_pointer))
+        return nullptr;
+
+      // Alleged frame pointer is readable, use it for further unwinding.
+      new_frame_pointer = pre_signal_frame_pointer;
+
+      // Skip frame size check if we return from a signal. We may be using a
+      // an alternate stack for signals.
+      check_frame_size = false;
+    }
+  }
+#endif
+
+  // aarch64 ABI requires stack pointer to be 16-byte-aligned.
+  if ((reinterpret_cast<uintptr_t>(new_frame_pointer) & 15) != 0)
+    return nullptr;
+
+  // Check frame size.  In strict mode, we assume frames to be under
+  // 100,000 bytes.  In non-strict mode, we relax the limit to 1MB.
+  if (check_frame_size) {
+    const uintptr_t max_size = STRICT_UNWINDING ? 100000 : 1000000;
+    const uintptr_t frame_size =
+        ComputeStackFrameSize(old_frame_pointer, new_frame_pointer);
+    if (frame_size == kUnknownFrameSize || frame_size > max_size)
+      return nullptr;
+  }
+
+  return new_frame_pointer;
+}
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void *ucp, int *min_dropped_frames) {
+#ifdef __GNUC__
+  void **frame_pointer = reinterpret_cast<void**>(__builtin_frame_address(0));
+#else
+# error reading stack point not yet supported on this platform.
+#endif
+
+  skip_count++;    // Skip the frame for this function.
+  int n = 0;
+
+  // The frame pointer points to low address of a frame.  The first 64-bit
+  // word of a frame points to the next frame up the call chain, which normally
+  // is just after the high address of the current frame.  The second word of
+  // a frame contains return adress of to the caller.   To find a pc value
+  // associated with the current frame, we need to go down a level in the call
+  // chain.  So we remember return the address of the last frame seen.  This
+  // does not work for the first stack frame, which belongs to UnwindImp() but
+  // we skip the frame for UnwindImp() anyway.
+  void* prev_return_address = nullptr;
+
+  while (frame_pointer && n < max_depth) {
+    // The absl::GetStackFrames routine is called when we are in some
+    // informational context (the failure signal handler for example).
+    // Use the non-strict unwinding rules to produce a stack trace
+    // that is as complete as possible (even if it contains a few bogus
+    // entries in some rare cases).
+    void **next_frame_pointer =
+        NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp);
+
+    if (skip_count > 0) {
+      skip_count--;
+    } else {
+      result[n] = prev_return_address;
+      if (IS_STACK_FRAMES) {
+        sizes[n] = ComputeStackFrameSize(frame_pointer, next_frame_pointer);
+      }
+      n++;
+    }
+    prev_return_address = frame_pointer[1];
+    frame_pointer = next_frame_pointer;
+  }
+  if (min_dropped_frames != nullptr) {
+    // Implementation detail: we clamp the max of frames we are willing to
+    // count, so as not to spend too much time in the loop below.
+    const int kMaxUnwind = 200;
+    int j = 0;
+    for (; frame_pointer != nullptr && j < kMaxUnwind; j++) {
+      frame_pointer =
+          NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp);
+    }
+    *min_dropped_frames = j;
+  }
+  return n;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return true;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_AARCH64_INL_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_arm-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_arm-inl.inc
new file mode 100644
index 000000000000..2a1bf2e88694
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_arm-inl.inc
@@ -0,0 +1,134 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This is inspired by Craig Silverstein's PowerPC stacktrace code.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_ARM_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_ARM_INL_H_
+
+#include <cstdint>
+
+#include "absl/debugging/stacktrace.h"
+
+// WARNING:
+// This only works if all your code is in either ARM or THUMB mode.  With
+// interworking, the frame pointer of the caller can either be in r11 (ARM
+// mode) or r7 (THUMB mode).  A callee only saves the frame pointer of its
+// mode in a fixed location on its stack frame.  If the caller is a different
+// mode, there is no easy way to find the frame pointer.  It can either be
+// still in the designated register or saved on stack along with other callee
+// saved registers.
+
+// Given a pointer to a stack frame, locate and return the calling
+// stackframe, or return nullptr if no stackframe can be found. Perform sanity
+// checks (the strictness of which is controlled by the boolean parameter
+// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
+template<bool STRICT_UNWINDING>
+static void **NextStackFrame(void **old_sp) {
+  void **new_sp = (void**) old_sp[-1];
+
+  // Check that the transition from frame pointer old_sp to frame
+  // pointer new_sp isn't clearly bogus
+  if (STRICT_UNWINDING) {
+    // With the stack growing downwards, older stack frame must be
+    // at a greater address that the current one.
+    if (new_sp <= old_sp) return nullptr;
+    // Assume stack frames larger than 100,000 bytes are bogus.
+    if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return nullptr;
+  } else {
+    // In the non-strict mode, allow discontiguous stack frames.
+    // (alternate-signal-stacks for example).
+    if (new_sp == old_sp) return nullptr;
+    // And allow frames upto about 1MB.
+    if ((new_sp > old_sp)
+        && ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000)) return nullptr;
+  }
+  if ((uintptr_t)new_sp & (sizeof(void *) - 1)) return nullptr;
+  return new_sp;
+}
+
+// This ensures that absl::GetStackTrace sets up the Link Register properly.
+#ifdef __GNUC__
+void StacktraceArmDummyFunction() __attribute__((noinline));
+void StacktraceArmDummyFunction() { __asm__ volatile(""); }
+#else
+# error StacktraceArmDummyFunction() needs to be ported to this platform.
+#endif
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void * /* ucp */, int *min_dropped_frames) {
+#ifdef __GNUC__
+  void **sp = reinterpret_cast<void**>(__builtin_frame_address(0));
+#else
+# error reading stack point not yet supported on this platform.
+#endif
+
+  // On ARM, the return address is stored in the link register (r14).
+  // This is not saved on the stack frame of a leaf function.  To
+  // simplify code that reads return addresses, we call a dummy
+  // function so that the return address of this function is also
+  // stored in the stack frame.  This works at least for gcc.
+  StacktraceArmDummyFunction();
+
+  int n = 0;
+  while (sp && n < max_depth) {
+    // The absl::GetStackFrames routine is called when we are in some
+    // informational context (the failure signal handler for example).
+    // Use the non-strict unwinding rules to produce a stack trace
+    // that is as complete as possible (even if it contains a few bogus
+    // entries in some rare cases).
+    void **next_sp = NextStackFrame<!IS_STACK_FRAMES>(sp);
+
+    if (skip_count > 0) {
+      skip_count--;
+    } else {
+      result[n] = *sp;
+
+      if (IS_STACK_FRAMES) {
+        if (next_sp > sp) {
+          sizes[n] = (uintptr_t)next_sp - (uintptr_t)sp;
+        } else {
+          // A frame-size of 0 is used to indicate unknown frame size.
+          sizes[n] = 0;
+        }
+      }
+      n++;
+    }
+    sp = next_sp;
+  }
+  if (min_dropped_frames != nullptr) {
+    // Implementation detail: we clamp the max of frames we are willing to
+    // count, so as not to spend too much time in the loop below.
+    const int kMaxUnwind = 200;
+    int j = 0;
+    for (; sp != nullptr && j < kMaxUnwind; j++) {
+      sp = NextStackFrame<!IS_STACK_FRAMES>(sp);
+    }
+    *min_dropped_frames = j;
+  }
+  return n;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return false;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_ARM_INL_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_config.h b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_config.h
new file mode 100644
index 000000000000..d4e8480a8e28
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_config.h
@@ -0,0 +1,70 @@
+/*
+ * Copyright 2017 The Abseil Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+
+ * Defines ABSL_STACKTRACE_INL_HEADER to the *-inl.h containing
+ * actual unwinder implementation.
+ * This header is "private" to stacktrace.cc.
+ * DO NOT include it into any other files.
+*/
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_CONFIG_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_CONFIG_H_
+
+#if defined(ABSL_STACKTRACE_INL_HEADER)
+#error ABSL_STACKTRACE_INL_HEADER cannot be directly set
+
+#elif defined(_WIN32)
+#define ABSL_STACKTRACE_INL_HEADER \
+    "absl/debugging/internal/stacktrace_win32-inl.inc"
+
+#elif defined(__linux__) && !defined(__ANDROID__)
+
+#if !defined(NO_FRAME_POINTER)
+# if defined(__i386__) || defined(__x86_64__)
+#define ABSL_STACKTRACE_INL_HEADER \
+    "absl/debugging/internal/stacktrace_x86-inl.inc"
+# elif defined(__ppc__) || defined(__PPC__)
+#define ABSL_STACKTRACE_INL_HEADER \
+    "absl/debugging/internal/stacktrace_powerpc-inl.inc"
+# elif defined(__aarch64__)
+#define ABSL_STACKTRACE_INL_HEADER \
+    "absl/debugging/internal/stacktrace_aarch64-inl.inc"
+# elif defined(__arm__)
+// Note: When using glibc this may require -funwind-tables to function properly.
+#define ABSL_STACKTRACE_INL_HEADER \
+  "absl/debugging/internal/stacktrace_generic-inl.inc"
+# else
+#define ABSL_STACKTRACE_INL_HEADER \
+   "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
+# endif
+#else  // defined(NO_FRAME_POINTER)
+# if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__)
+#define ABSL_STACKTRACE_INL_HEADER \
+    "absl/debugging/internal/stacktrace_generic-inl.inc"
+# elif defined(__ppc__) || defined(__PPC__)
+#define ABSL_STACKTRACE_INL_HEADER \
+    "absl/debugging/internal/stacktrace_generic-inl.inc"
+# else
+#define ABSL_STACKTRACE_INL_HEADER \
+   "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
+# endif
+#endif  // NO_FRAME_POINTER
+
+#else
+#define ABSL_STACKTRACE_INL_HEADER \
+  "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
+
+#endif
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_CONFIG_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_generic-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_generic-inl.inc
new file mode 100644
index 000000000000..b2792a1f3ada
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_generic-inl.inc
@@ -0,0 +1,108 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Portable implementation - just use glibc
+//
+// Note:  The glibc implementation may cause a call to malloc.
+// This can cause a deadlock in HeapProfiler.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_
+
+#include <execinfo.h>
+#include <atomic>
+#include <cstring>
+
+#include "absl/debugging/stacktrace.h"
+#include "absl/base/attributes.h"
+
+// Sometimes, we can try to get a stack trace from within a stack
+// trace, because we don't block signals inside this code (which would be too
+// expensive: the two extra system calls per stack trace do matter here).
+// That can cause a self-deadlock.
+// Protect against such reentrant call by failing to get a stack trace.
+//
+// We use __thread here because the code here is extremely low level -- it is
+// called while collecting stack traces from within malloc and mmap, and thus
+// can not call anything which might call malloc or mmap itself.
+static __thread int recursive = 0;
+
+// The stack trace function might be invoked very early in the program's
+// execution (e.g. from the very first malloc if using tcmalloc). Also, the
+// glibc implementation itself will trigger malloc the first time it is called.
+// As such, we suppress usage of backtrace during this early stage of execution.
+static std::atomic<bool> disable_stacktraces(true);  // Disabled until healthy.
+// Waiting until static initializers run seems to be late enough.
+// This file is included into stacktrace.cc so this will only run once.
+ABSL_ATTRIBUTE_UNUSED static int stacktraces_enabler = []() {
+  void* unused_stack[1];
+  // Force the first backtrace to happen early to get the one-time shared lib
+  // loading (allocation) out of the way. After the first call it is much safer
+  // to use backtrace from a signal handler if we crash somewhere later.
+  backtrace(unused_stack, 1);
+  disable_stacktraces.store(false, std::memory_order_relaxed);
+  return 0;
+}();
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void *ucp, int *min_dropped_frames) {
+  if (recursive || disable_stacktraces.load(std::memory_order_relaxed)) {
+    return 0;
+  }
+  ++recursive;
+
+  static_cast<void>(ucp);  // Unused.
+  static const int kStackLength = 64;
+  void * stack[kStackLength];
+  int size;
+
+  size = backtrace(stack, kStackLength);
+  skip_count++;  // we want to skip the current frame as well
+  int result_count = size - skip_count;
+  if (result_count < 0)
+    result_count = 0;
+  if (result_count > max_depth)
+    result_count = max_depth;
+  for (int i = 0; i < result_count; i++)
+    result[i] = stack[i + skip_count];
+
+  if (IS_STACK_FRAMES) {
+    // No implementation for finding out the stack frame sizes yet.
+    memset(sizes, 0, sizeof(*sizes) * result_count);
+  }
+  if (min_dropped_frames != nullptr) {
+    if (size - skip_count - max_depth > 0) {
+      *min_dropped_frames = size - skip_count - max_depth;
+    } else {
+      *min_dropped_frames = 0;
+    }
+  }
+
+  --recursive;
+
+  return result_count;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return true;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_GENERIC_INL_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_powerpc-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_powerpc-inl.inc
new file mode 100644
index 000000000000..2e7c2f404f20
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_powerpc-inl.inc
@@ -0,0 +1,248 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Produce stack trace.  I'm guessing (hoping!) the code is much like
+// for x86.  For apple machines, at least, it seems to be; see
+//    https://developer.apple.com/documentation/mac/runtimehtml/RTArch-59.html
+//    https://www.linux-foundation.org/spec/ELF/ppc64/PPC-elf64abi-1.9.html#STACK
+// Linux has similar code: http://patchwork.ozlabs.org/linuxppc/patch?id=8882
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_POWERPC_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_POWERPC_INL_H_
+
+#if defined(__linux__)
+#include <asm/ptrace.h>   // for PT_NIP.
+#include <ucontext.h>     // for ucontext_t
+#endif
+
+#include <unistd.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
+
+#include "absl/base/attributes.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+#include "absl/debugging/stacktrace.h"
+#include "absl/debugging/internal/address_is_readable.h"
+#include "absl/debugging/internal/vdso_support.h"  // a no-op on non-elf or non-glibc systems
+
+// Given a stack pointer, return the saved link register value.
+// Note that this is the link register for a callee.
+static inline void *StacktracePowerPCGetLR(void **sp) {
+  // PowerPC has 3 main ABIs, which say where in the stack the
+  // Link Register is.  For DARWIN and AIX (used by apple and
+  // linux ppc64), it's in sp[2].  For SYSV (used by linux ppc),
+  // it's in sp[1].
+#if defined(_CALL_AIX) || defined(_CALL_DARWIN)
+  return *(sp+2);
+#elif defined(_CALL_SYSV)
+  return *(sp+1);
+#elif defined(__APPLE__) || defined(__FreeBSD__) || \
+    (defined(__linux__) && defined(__PPC64__))
+  // This check is in case the compiler doesn't define _CALL_AIX/etc.
+  return *(sp+2);
+#elif defined(__linux)
+  // This check is in case the compiler doesn't define _CALL_SYSV.
+  return *(sp+1);
+#else
+#error Need to specify the PPC ABI for your archiecture.
+#endif
+}
+
+// Given a pointer to a stack frame, locate and return the calling
+// stackframe, or return null if no stackframe can be found. Perform sanity
+// checks (the strictness of which is controlled by the boolean parameter
+// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
+template<bool STRICT_UNWINDING, bool IS_WITH_CONTEXT>
+ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
+static void **NextStackFrame(void **old_sp, const void *uc) {
+  void **new_sp = (void **) *old_sp;
+  enum { kStackAlignment = 16 };
+
+  // Check that the transition from frame pointer old_sp to frame
+  // pointer new_sp isn't clearly bogus
+  if (STRICT_UNWINDING) {
+    // With the stack growing downwards, older stack frame must be
+    // at a greater address that the current one.
+    if (new_sp <= old_sp) return nullptr;
+    // Assume stack frames larger than 100,000 bytes are bogus.
+    if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return nullptr;
+  } else {
+    // In the non-strict mode, allow discontiguous stack frames.
+    // (alternate-signal-stacks for example).
+    if (new_sp == old_sp) return nullptr;
+    // And allow frames upto about 1MB.
+    if ((new_sp > old_sp)
+        && ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000)) return nullptr;
+  }
+  if ((uintptr_t)new_sp % kStackAlignment != 0) return nullptr;
+
+#if defined(__linux__)
+  enum StackTraceKernelSymbolStatus {
+      kNotInitialized = 0, kAddressValid, kAddressInvalid };
+
+  if (IS_WITH_CONTEXT && uc != nullptr) {
+    static StackTraceKernelSymbolStatus kernel_symbol_status =
+        kNotInitialized;  // Sentinel: not computed yet.
+    // Initialize with sentinel value: __kernel_rt_sigtramp_rt64 can not
+    // possibly be there.
+    static const unsigned char *kernel_sigtramp_rt64_address = nullptr;
+    if (kernel_symbol_status == kNotInitialized) {
+      absl::debugging_internal::VDSOSupport vdso;
+      if (vdso.IsPresent()) {
+        absl::debugging_internal::VDSOSupport::SymbolInfo
+            sigtramp_rt64_symbol_info;
+        if (!vdso.LookupSymbol(
+                "__kernel_sigtramp_rt64", "LINUX_2.6.15",
+                absl::debugging_internal::VDSOSupport::kVDSOSymbolType,
+                &sigtramp_rt64_symbol_info) ||
+            sigtramp_rt64_symbol_info.address == nullptr) {
+          // Unexpected: VDSO is present, yet the expected symbol is missing
+          // or null.
+          assert(false && "VDSO is present, but doesn't have expected symbol");
+          kernel_symbol_status = kAddressInvalid;
+        } else {
+          kernel_sigtramp_rt64_address =
+              reinterpret_cast<const unsigned char *>(
+                  sigtramp_rt64_symbol_info.address);
+          kernel_symbol_status = kAddressValid;
+        }
+      } else {
+        kernel_symbol_status = kAddressInvalid;
+      }
+    }
+
+    if (new_sp != nullptr &&
+        kernel_symbol_status == kAddressValid &&
+        StacktracePowerPCGetLR(new_sp) == kernel_sigtramp_rt64_address) {
+      const ucontext_t* signal_context =
+          reinterpret_cast<const ucontext_t*>(uc);
+      void **const sp_before_signal =
+          reinterpret_cast<void**>(signal_context->uc_mcontext.gp_regs[PT_R1]);
+      // Check that alleged sp before signal is nonnull and is reasonably
+      // aligned.
+      if (sp_before_signal != nullptr &&
+          ((uintptr_t)sp_before_signal % kStackAlignment) == 0) {
+        // Check that alleged stack pointer is actually readable. This is to
+        // prevent a "double fault" in case we hit the first fault due to e.g.
+        // a stack corruption.
+        if (absl::debugging_internal::AddressIsReadable(sp_before_signal)) {
+          // Alleged stack pointer is readable, use it for further unwinding.
+          new_sp = sp_before_signal;
+        }
+      }
+    }
+  }
+#endif
+
+  return new_sp;
+}
+
+// This ensures that absl::GetStackTrace sets up the Link Register properly.
+ABSL_ATTRIBUTE_NOINLINE static void AbslStacktracePowerPCDummyFunction() {
+  ABSL_BLOCK_TAIL_CALL_OPTIMIZATION();
+}
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void *ucp, int *min_dropped_frames) {
+  void **sp;
+  // Apple macOS uses an old version of gnu as -- both Darwin 7.9.0 (Panther)
+  // and Darwin 8.8.1 (Tiger) use as 1.38.  This means we have to use a
+  // different asm syntax.  I don't know quite the best way to discriminate
+  // systems using the old as from the new one; I've gone with __APPLE__.
+#ifdef __APPLE__
+  __asm__ volatile ("mr %0,r1" : "=r" (sp));
+#else
+  __asm__ volatile ("mr %0,1" : "=r" (sp));
+#endif
+
+  // On PowerPC, the "Link Register" or "Link Record" (LR), is a stack
+  // entry that holds the return address of the subroutine call (what
+  // instruction we run after our function finishes).  This is the
+  // same as the stack-pointer of our parent routine, which is what we
+  // want here.  While the compiler will always(?) set up LR for
+  // subroutine calls, it may not for leaf functions (such as this one).
+  // This routine forces the compiler (at least gcc) to push it anyway.
+  AbslStacktracePowerPCDummyFunction();
+
+  // The LR save area is used by the callee, so the top entry is bogus.
+  skip_count++;
+
+  int n = 0;
+
+  // Unlike ABIs of X86 and ARM, PowerPC ABIs say that return address (in
+  // the link register) of a function call is stored in the caller's stack
+  // frame instead of the callee's.  When we look for the return address
+  // associated with a stack frame, we need to make sure that there is a
+  // caller frame before it.  So we call NextStackFrame before entering the
+  // loop below and check next_sp instead of sp for loop termination.
+  // The outermost frame is set up by runtimes and it does not have a
+  // caller frame, so it is skipped.
+
+  // The absl::GetStackFrames routine is called when we are in some
+  // informational context (the failure signal handler for example).
+  // Use the non-strict unwinding rules to produce a stack trace
+  // that is as complete as possible (even if it contains a few
+  // bogus entries in some rare cases).
+  void **next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(sp, ucp);
+
+  while (next_sp && n < max_depth) {
+    if (skip_count > 0) {
+      skip_count--;
+    } else {
+      result[n] = StacktracePowerPCGetLR(sp);
+      if (IS_STACK_FRAMES) {
+        if (next_sp > sp) {
+          sizes[n] = (uintptr_t)next_sp - (uintptr_t)sp;
+        } else {
+          // A frame-size of 0 is used to indicate unknown frame size.
+          sizes[n] = 0;
+        }
+      }
+      n++;
+    }
+
+    sp = next_sp;
+    next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(sp, ucp);
+  }
+
+  if (min_dropped_frames != nullptr) {
+    // Implementation detail: we clamp the max of frames we are willing to
+    // count, so as not to spend too much time in the loop below.
+    const int kMaxUnwind = 1000;
+    int j = 0;
+    for (; next_sp != nullptr && j < kMaxUnwind; j++) {
+      next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(next_sp, ucp);
+    }
+    *min_dropped_frames = j;
+  }
+  return n;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return true;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_POWERPC_INL_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_unimplemented-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_unimplemented-inl.inc
new file mode 100644
index 000000000000..5b8fb191b65a
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_unimplemented-inl.inc
@@ -0,0 +1,24 @@
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_UNIMPLEMENTED_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_UNIMPLEMENTED_INL_H_
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void** /* result */, int* /* sizes */,
+                      int /* max_depth */, int /* skip_count */,
+                      const void* /* ucp */, int *min_dropped_frames) {
+  if (min_dropped_frames != nullptr) {
+    *min_dropped_frames = 0;
+  }
+  return 0;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return false;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_UNIMPLEMENTED_INL_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_win32-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_win32-inl.inc
new file mode 100644
index 000000000000..1c666c8b561f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_win32-inl.inc
@@ -0,0 +1,93 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Produces a stack trace for Windows.  Normally, one could use
+// stacktrace_x86-inl.h or stacktrace_x86_64-inl.h -- and indeed, that
+// should work for binaries compiled using MSVC in "debug" mode.
+// However, in "release" mode, Windows uses frame-pointer
+// optimization, which makes getting a stack trace very difficult.
+//
+// There are several approaches one can take.  One is to use Windows
+// intrinsics like StackWalk64.  These can work, but have restrictions
+// on how successful they can be.  Another attempt is to write a
+// version of stacktrace_x86-inl.h that has heuristic support for
+// dealing with FPO, similar to what WinDbg does (see
+// http://www.nynaeve.net/?p=97).  There are (non-working) examples of
+// these approaches, complete with TODOs, in stacktrace_win32-inl.h#1
+//
+// The solution we've ended up doing is to call the undocumented
+// windows function RtlCaptureStackBackTrace, which probably doesn't
+// work with FPO but at least is fast, and doesn't require a symbol
+// server.
+//
+// This code is inspired by a patch from David Vitek:
+//   https://code.google.com/p/google-perftools/issues/detail?id=83
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_WIN32_INL_H_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_WIN32_INL_H_
+
+#include <windows.h>    // for GetProcAddress and GetModuleHandle
+#include <cassert>
+
+typedef USHORT NTAPI RtlCaptureStackBackTrace_Function(
+    IN ULONG frames_to_skip,
+    IN ULONG frames_to_capture,
+    OUT PVOID *backtrace,
+    OUT PULONG backtrace_hash);
+
+// It is not possible to load RtlCaptureStackBackTrace at static init time in
+// UWP. CaptureStackBackTrace is the public version of RtlCaptureStackBackTrace
+#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP) && \
+    !WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+static RtlCaptureStackBackTrace_Function* const RtlCaptureStackBackTrace_fn =
+    &::CaptureStackBackTrace;
+#else
+// Load the function we need at static init time, where we don't have
+// to worry about someone else holding the loader's lock.
+static RtlCaptureStackBackTrace_Function* const RtlCaptureStackBackTrace_fn =
+    (RtlCaptureStackBackTrace_Function*)GetProcAddress(
+        GetModuleHandleA("ntdll.dll"), "RtlCaptureStackBackTrace");
+#endif  // WINAPI_PARTITION_APP && !WINAPI_PARTITION_DESKTOP
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
+                      const void*, int* min_dropped_frames) {
+  int n = 0;
+  if (!RtlCaptureStackBackTrace_fn) {
+    // can't find a stacktrace with no function to call
+  } else {
+    n = (int)RtlCaptureStackBackTrace_fn(skip_count + 2, max_depth, result, 0);
+  }
+  if (IS_STACK_FRAMES) {
+    // No implementation for finding out the stack frame sizes yet.
+    memset(sizes, 0, sizeof(*sizes) * n);
+  }
+  if (min_dropped_frames != nullptr) {
+    // Not implemented.
+    *min_dropped_frames = 0;
+  }
+  return n;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return false;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_WIN32_INL_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/stacktrace_x86-inl.inc b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_x86-inl.inc
new file mode 100644
index 000000000000..bc320ff75bc5
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/stacktrace_x86-inl.inc
@@ -0,0 +1,346 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Produce stack trace
+
+#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_X86_INL_INC_
+#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_X86_INL_INC_
+
+#if defined(__linux__) && (defined(__i386__) || defined(__x86_64__))
+#include <ucontext.h>  // for ucontext_t
+#endif
+
+#if !defined(_WIN32)
+#include <unistd.h>
+#endif
+
+#include <cassert>
+#include <cstdint>
+
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/debugging/internal/address_is_readable.h"
+#include "absl/debugging/internal/vdso_support.h"  // a no-op on non-elf or non-glibc systems
+#include "absl/debugging/stacktrace.h"
+
+#include "absl/base/internal/raw_logging.h"
+
+using absl::debugging_internal::AddressIsReadable;
+
+#if defined(__linux__) && defined(__i386__)
+// Count "push %reg" instructions in VDSO __kernel_vsyscall(),
+// preceeding "syscall" or "sysenter".
+// If __kernel_vsyscall uses frame pointer, answer 0.
+//
+// kMaxBytes tells how many instruction bytes of __kernel_vsyscall
+// to analyze before giving up. Up to kMaxBytes+1 bytes of
+// instructions could be accessed.
+//
+// Here are known __kernel_vsyscall instruction sequences:
+//
+// SYSENTER (linux-2.6.26/arch/x86/vdso/vdso32/sysenter.S).
+// Used on Intel.
+//  0xffffe400 <__kernel_vsyscall+0>:       push   %ecx
+//  0xffffe401 <__kernel_vsyscall+1>:       push   %edx
+//  0xffffe402 <__kernel_vsyscall+2>:       push   %ebp
+//  0xffffe403 <__kernel_vsyscall+3>:       mov    %esp,%ebp
+//  0xffffe405 <__kernel_vsyscall+5>:       sysenter
+//
+// SYSCALL (see linux-2.6.26/arch/x86/vdso/vdso32/syscall.S).
+// Used on AMD.
+//  0xffffe400 <__kernel_vsyscall+0>:       push   %ebp
+//  0xffffe401 <__kernel_vsyscall+1>:       mov    %ecx,%ebp
+//  0xffffe403 <__kernel_vsyscall+3>:       syscall
+//
+
+// The sequence below isn't actually expected in Google fleet,
+// here only for completeness. Remove this comment from OSS release.
+
+// i386 (see linux-2.6.26/arch/x86/vdso/vdso32/int80.S)
+//  0xffffe400 <__kernel_vsyscall+0>:       int $0x80
+//  0xffffe401 <__kernel_vsyscall+1>:       ret
+//
+static const int kMaxBytes = 10;
+
+// We use assert()s instead of DCHECK()s -- this is too low level
+// for DCHECK().
+
+static int CountPushInstructions(const unsigned char *const addr) {
+  int result = 0;
+  for (int i = 0; i < kMaxBytes; ++i) {
+    if (addr[i] == 0x89) {
+      // "mov reg,reg"
+      if (addr[i + 1] == 0xE5) {
+        // Found "mov %esp,%ebp".
+        return 0;
+      }
+      ++i;  // Skip register encoding byte.
+    } else if (addr[i] == 0x0F &&
+               (addr[i + 1] == 0x34 || addr[i + 1] == 0x05)) {
+      // Found "sysenter" or "syscall".
+      return result;
+    } else if ((addr[i] & 0xF0) == 0x50) {
+      // Found "push %reg".
+      ++result;
+    } else if (addr[i] == 0xCD && addr[i + 1] == 0x80) {
+      // Found "int $0x80"
+      assert(result == 0);
+      return 0;
+    } else {
+      // Unexpected instruction.
+      assert(false && "unexpected instruction in __kernel_vsyscall");
+      return 0;
+    }
+  }
+  // Unexpected: didn't find SYSENTER or SYSCALL in
+  // [__kernel_vsyscall, __kernel_vsyscall + kMaxBytes) interval.
+  assert(false && "did not find SYSENTER or SYSCALL in __kernel_vsyscall");
+  return 0;
+}
+#endif
+
+// Assume stack frames larger than 100,000 bytes are bogus.
+static const int kMaxFrameBytes = 100000;
+
+// Returns the stack frame pointer from signal context, 0 if unknown.
+// vuc is a ucontext_t *.  We use void* to avoid the use
+// of ucontext_t on non-POSIX systems.
+static uintptr_t GetFP(const void *vuc) {
+#if !defined(__linux__)
+  static_cast<void>(vuc);  // Avoid an unused argument compiler warning.
+#else
+  if (vuc != nullptr) {
+    auto *uc = reinterpret_cast<const ucontext_t *>(vuc);
+#if defined(__i386__)
+    const auto bp = uc->uc_mcontext.gregs[REG_EBP];
+    const auto sp = uc->uc_mcontext.gregs[REG_ESP];
+#elif defined(__x86_64__)
+    const auto bp = uc->uc_mcontext.gregs[REG_RBP];
+    const auto sp = uc->uc_mcontext.gregs[REG_RSP];
+#else
+    const uintptr_t bp = 0;
+    const uintptr_t sp = 0;
+#endif
+    // Sanity-check that the base pointer is valid.  It should be as long as
+    // SHRINK_WRAP_FRAME_POINTER is not set, but it's possible that some code in
+    // the process is compiled with --copt=-fomit-frame-pointer or
+    // --copt=-momit-leaf-frame-pointer.
+    //
+    // TODO(bcmills): -momit-leaf-frame-pointer is currently the default
+    // behavior when building with clang.  Talk to the C++ toolchain team about
+    // fixing that.
+    if (bp >= sp && bp - sp <= kMaxFrameBytes) return bp;
+
+    // If bp isn't a plausible frame pointer, return the stack pointer instead.
+    // If we're lucky, it points to the start of a stack frame; otherwise, we'll
+    // get one frame of garbage in the stack trace and fail the sanity check on
+    // the next iteration.
+    return sp;
+  }
+#endif
+  return 0;
+}
+
+// Given a pointer to a stack frame, locate and return the calling
+// stackframe, or return null if no stackframe can be found. Perform sanity
+// checks (the strictness of which is controlled by the boolean parameter
+// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
+template <bool STRICT_UNWINDING, bool WITH_CONTEXT>
+ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
+static void **NextStackFrame(void **old_fp, const void *uc) {
+  void **new_fp = (void **)*old_fp;
+
+#if defined(__linux__) && defined(__i386__)
+  if (WITH_CONTEXT && uc != nullptr) {
+    // How many "push %reg" instructions are there at __kernel_vsyscall?
+    // This is constant for a given kernel and processor, so compute
+    // it only once.
+    static int num_push_instructions = -1;  // Sentinel: not computed yet.
+    // Initialize with sentinel value: __kernel_rt_sigreturn can not possibly
+    // be there.
+    static const unsigned char *kernel_rt_sigreturn_address = nullptr;
+    static const unsigned char *kernel_vsyscall_address = nullptr;
+    if (num_push_instructions == -1) {
+#ifdef ABSL_HAVE_VDSO_SUPPORT
+      absl::debugging_internal::VDSOSupport vdso;
+      if (vdso.IsPresent()) {
+        absl::debugging_internal::VDSOSupport::SymbolInfo
+            rt_sigreturn_symbol_info;
+        absl::debugging_internal::VDSOSupport::SymbolInfo vsyscall_symbol_info;
+        if (!vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_2.5", STT_FUNC,
+                               &rt_sigreturn_symbol_info) ||
+            !vdso.LookupSymbol("__kernel_vsyscall", "LINUX_2.5", STT_FUNC,
+                               &vsyscall_symbol_info) ||
+            rt_sigreturn_symbol_info.address == nullptr ||
+            vsyscall_symbol_info.address == nullptr) {
+          // Unexpected: 32-bit VDSO is present, yet one of the expected
+          // symbols is missing or null.
+          assert(false && "VDSO is present, but doesn't have expected symbols");
+          num_push_instructions = 0;
+        } else {
+          kernel_rt_sigreturn_address =
+              reinterpret_cast<const unsigned char *>(
+                  rt_sigreturn_symbol_info.address);
+          kernel_vsyscall_address =
+              reinterpret_cast<const unsigned char *>(
+                  vsyscall_symbol_info.address);
+          num_push_instructions =
+              CountPushInstructions(kernel_vsyscall_address);
+        }
+      } else {
+        num_push_instructions = 0;
+      }
+#else  // ABSL_HAVE_VDSO_SUPPORT
+      num_push_instructions = 0;
+#endif  // ABSL_HAVE_VDSO_SUPPORT
+    }
+    if (num_push_instructions != 0 && kernel_rt_sigreturn_address != nullptr &&
+        old_fp[1] == kernel_rt_sigreturn_address) {
+      const ucontext_t *ucv = static_cast<const ucontext_t *>(uc);
+      // This kernel does not use frame pointer in its VDSO code,
+      // and so %ebp is not suitable for unwinding.
+      void **const reg_ebp =
+          reinterpret_cast<void **>(ucv->uc_mcontext.gregs[REG_EBP]);
+      const unsigned char *const reg_eip =
+          reinterpret_cast<unsigned char *>(ucv->uc_mcontext.gregs[REG_EIP]);
+      if (new_fp == reg_ebp && kernel_vsyscall_address <= reg_eip &&
+          reg_eip - kernel_vsyscall_address < kMaxBytes) {
+        // We "stepped up" to __kernel_vsyscall, but %ebp is not usable.
+        // Restore from 'ucv' instead.
+        void **const reg_esp =
+            reinterpret_cast<void **>(ucv->uc_mcontext.gregs[REG_ESP]);
+        // Check that alleged %esp is not null and is reasonably aligned.
+        if (reg_esp &&
+            ((uintptr_t)reg_esp & (sizeof(reg_esp) - 1)) == 0) {
+          // Check that alleged %esp is actually readable. This is to prevent
+          // "double fault" in case we hit the first fault due to e.g. stack
+          // corruption.
+          void *const reg_esp2 = reg_esp[num_push_instructions - 1];
+          if (AddressIsReadable(reg_esp2)) {
+            // Alleged %esp is readable, use it for further unwinding.
+            new_fp = reinterpret_cast<void **>(reg_esp2);
+          }
+        }
+      }
+    }
+  }
+#endif
+
+  const uintptr_t old_fp_u = reinterpret_cast<uintptr_t>(old_fp);
+  const uintptr_t new_fp_u = reinterpret_cast<uintptr_t>(new_fp);
+
+  // Check that the transition from frame pointer old_fp to frame
+  // pointer new_fp isn't clearly bogus.  Skip the checks if new_fp
+  // matches the signal context, so that we don't skip out early when
+  // using an alternate signal stack.
+  //
+  // TODO(bcmills): The GetFP call should be completely unnecessary when
+  // SHRINK_WRAP_FRAME_POINTER is set (because we should be back in the thread's
+  // stack by this point), but it is empirically still needed (e.g. when the
+  // stack includes a call to abort).  unw_get_reg returns UNW_EBADREG for some
+  // frames.  Figure out why GetValidFrameAddr and/or libunwind isn't doing what
+  // it's supposed to.
+  if (STRICT_UNWINDING &&
+      (!WITH_CONTEXT || uc == nullptr || new_fp_u != GetFP(uc))) {
+    // With the stack growing downwards, older stack frame must be
+    // at a greater address that the current one.
+    if (new_fp_u <= old_fp_u) return nullptr;
+    if (new_fp_u - old_fp_u > kMaxFrameBytes) return nullptr;
+  } else {
+    if (new_fp == nullptr) return nullptr;  // skip AddressIsReadable() below
+    // In the non-strict mode, allow discontiguous stack frames.
+    // (alternate-signal-stacks for example).
+    if (new_fp == old_fp) return nullptr;
+  }
+
+  if (new_fp_u & (sizeof(void *) - 1)) return nullptr;
+#ifdef __i386__
+  // On 32-bit machines, the stack pointer can be very close to
+  // 0xffffffff, so we explicitly check for a pointer into the
+  // last two pages in the address space
+  if (new_fp_u >= 0xffffe000) return nullptr;
+#endif
+#if !defined(_WIN32)
+  if (!STRICT_UNWINDING) {
+    // Lax sanity checks cause a crash in 32-bit tcmalloc/crash_reason_test
+    // on AMD-based machines with VDSO-enabled kernels.
+    // Make an extra sanity check to insure new_fp is readable.
+    // Note: NextStackFrame<false>() is only called while the program
+    //       is already on its last leg, so it's ok to be slow here.
+
+    if (!AddressIsReadable(new_fp)) {
+      return nullptr;
+    }
+  }
+#endif
+  return new_fp;
+}
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
+ABSL_ATTRIBUTE_NOINLINE
+static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
+                      const void *ucp, int *min_dropped_frames) {
+  int n = 0;
+  void **fp = reinterpret_cast<void **>(__builtin_frame_address(0));
+
+  while (fp && n < max_depth) {
+    if (*(fp + 1) == reinterpret_cast<void *>(0)) {
+      // In 64-bit code, we often see a frame that
+      // points to itself and has a return address of 0.
+      break;
+    }
+    void **next_fp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(fp, ucp);
+    if (skip_count > 0) {
+      skip_count--;
+    } else {
+      result[n] = *(fp + 1);
+      if (IS_STACK_FRAMES) {
+        if (next_fp > fp) {
+          sizes[n] = (uintptr_t)next_fp - (uintptr_t)fp;
+        } else {
+          // A frame-size of 0 is used to indicate unknown frame size.
+          sizes[n] = 0;
+        }
+      }
+      n++;
+    }
+    fp = next_fp;
+  }
+  if (min_dropped_frames != nullptr) {
+    // Implementation detail: we clamp the max of frames we are willing to
+    // count, so as not to spend too much time in the loop below.
+    const int kMaxUnwind = 1000;
+    int j = 0;
+    for (; fp != nullptr && j < kMaxUnwind; j++) {
+      fp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(fp, ucp);
+    }
+    *min_dropped_frames = j;
+  }
+  return n;
+}
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+bool StackTraceWorksForTest() {
+  return true;
+}
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_STACKTRACE_X86_INL_INC_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/symbolize.h b/third_party/abseil_cpp/absl/debugging/internal/symbolize.h
new file mode 100644
index 000000000000..5d0858b5c7e1
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/symbolize.h
@@ -0,0 +1,128 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file contains internal parts of the Abseil symbolizer.
+// Do not depend on the anything in this file, it may change at anytime.
+
+#ifndef ABSL_DEBUGGING_INTERNAL_SYMBOLIZE_H_
+#define ABSL_DEBUGGING_INTERNAL_SYMBOLIZE_H_
+
+#include <cstddef>
+#include <cstdint>
+
+#include "absl/base/config.h"
+
+#ifdef ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE
+#error ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE cannot be directly set
+#elif defined(__ELF__) && defined(__GLIBC__) && !defined(__native_client__) && \
+    !defined(__asmjs__) && !defined(__wasm__)
+#define ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE 1
+
+#include <elf.h>
+#include <link.h>  // For ElfW() macro.
+#include <functional>
+#include <string>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// Iterates over all sections, invoking callback on each with the section name
+// and the section header.
+//
+// Returns true on success; otherwise returns false in case of errors.
+//
+// This is not async-signal-safe.
+bool ForEachSection(int fd,
+                    const std::function<bool(const std::string& name,
+                                             const ElfW(Shdr) &)>& callback);
+
+// Gets the section header for the given name, if it exists. Returns true on
+// success. Otherwise, returns false.
+bool GetSectionHeaderByName(int fd, const char *name, size_t name_len,
+                            ElfW(Shdr) *out);
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+struct SymbolDecoratorArgs {
+  // The program counter we are getting symbolic name for.
+  const void *pc;
+  // 0 for main executable, load address for shared libraries.
+  ptrdiff_t relocation;
+  // Read-only file descriptor for ELF image covering "pc",
+  // or -1 if no such ELF image exists in /proc/self/maps.
+  int fd;
+  // Output buffer, size.
+  // Note: the buffer may not be empty -- default symbolizer may have already
+  // produced some output, and earlier decorators may have adorned it in
+  // some way. You are free to replace or augment the contents (within the
+  // symbol_buf_size limit).
+  char *const symbol_buf;
+  size_t symbol_buf_size;
+  // Temporary scratch space, size.
+  // Use that space in preference to allocating your own stack buffer to
+  // conserve stack.
+  char *const tmp_buf;
+  size_t tmp_buf_size;
+  // User-provided argument
+  void* arg;
+};
+using SymbolDecorator = void (*)(const SymbolDecoratorArgs *);
+
+// Installs a function-pointer as a decorator. Returns a value less than zero
+// if the system cannot install the decorator. Otherwise, returns a unique
+// identifier corresponding to the decorator. This identifier can be used to
+// uninstall the decorator - See RemoveSymbolDecorator() below.
+int InstallSymbolDecorator(SymbolDecorator decorator, void* arg);
+
+// Removes a previously installed function-pointer decorator. Parameter "ticket"
+// is the return-value from calling InstallSymbolDecorator().
+bool RemoveSymbolDecorator(int ticket);
+
+// Remove all installed decorators.  Returns true if successful, false if
+// symbolization is currently in progress.
+bool RemoveAllSymbolDecorators(void);
+
+// Registers an address range to a file mapping.
+//
+// Preconditions:
+//   start <= end
+//   filename != nullptr
+//
+// Returns true if the file was successfully registered.
+bool RegisterFileMappingHint(
+    const void* start, const void* end, uint64_t offset, const char* filename);
+
+// Looks up the file mapping registered by RegisterFileMappingHint for an
+// address range. If there is one, the file name is stored in *filename and
+// *start and *end are modified to reflect the registered mapping. Returns
+// whether any hint was found.
+bool GetFileMappingHint(const void** start,
+                        const void** end,
+                        uint64_t    *  offset,
+                        const char** filename);
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_INTERNAL_SYMBOLIZE_H_
diff --git a/third_party/abseil_cpp/absl/debugging/internal/vdso_support.cc b/third_party/abseil_cpp/absl/debugging/internal/vdso_support.cc
new file mode 100644
index 000000000000..1e8a78ac9c1f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/vdso_support.cc
@@ -0,0 +1,194 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Allow dynamic symbol lookup in the kernel VDSO page.
+//
+// VDSOSupport -- a class representing kernel VDSO (if present).
+
+#include "absl/debugging/internal/vdso_support.h"
+
+#ifdef ABSL_HAVE_VDSO_SUPPORT     // defined in vdso_support.h
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#if __GLIBC_PREREQ(2, 16)  // GLIBC-2.16 implements getauxval.
+#include <sys/auxv.h>
+#endif
+
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/port.h"
+
+#ifndef AT_SYSINFO_EHDR
+#define AT_SYSINFO_EHDR 33  // for crosstoolv10
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+ABSL_CONST_INIT
+std::atomic<const void *> VDSOSupport::vdso_base_(
+    debugging_internal::ElfMemImage::kInvalidBase);
+
+std::atomic<VDSOSupport::GetCpuFn> VDSOSupport::getcpu_fn_(&InitAndGetCPU);
+VDSOSupport::VDSOSupport()
+    // If vdso_base_ is still set to kInvalidBase, we got here
+    // before VDSOSupport::Init has been called. Call it now.
+    : image_(vdso_base_.load(std::memory_order_relaxed) ==
+                     debugging_internal::ElfMemImage::kInvalidBase
+                 ? Init()
+                 : vdso_base_.load(std::memory_order_relaxed)) {}
+
+// NOTE: we can't use GoogleOnceInit() below, because we can be
+// called by tcmalloc, and none of the *once* stuff may be functional yet.
+//
+// In addition, we hope that the VDSOSupportHelper constructor
+// causes this code to run before there are any threads, and before
+// InitGoogle() has executed any chroot or setuid calls.
+//
+// Finally, even if there is a race here, it is harmless, because
+// the operation should be idempotent.
+const void *VDSOSupport::Init() {
+  const auto kInvalidBase = debugging_internal::ElfMemImage::kInvalidBase;
+#if __GLIBC_PREREQ(2, 16)
+  if (vdso_base_.load(std::memory_order_relaxed) == kInvalidBase) {
+    errno = 0;
+    const void *const sysinfo_ehdr =
+        reinterpret_cast<const void *>(getauxval(AT_SYSINFO_EHDR));
+    if (errno == 0) {
+      vdso_base_.store(sysinfo_ehdr, std::memory_order_relaxed);
+    }
+  }
+#endif  // __GLIBC_PREREQ(2, 16)
+  if (vdso_base_.load(std::memory_order_relaxed) == kInvalidBase) {
+    // Valgrind zaps AT_SYSINFO_EHDR and friends from the auxv[]
+    // on stack, and so glibc works as if VDSO was not present.
+    // But going directly to kernel via /proc/self/auxv below bypasses
+    // Valgrind zapping. So we check for Valgrind separately.
+    if (RunningOnValgrind()) {
+      vdso_base_.store(nullptr, std::memory_order_relaxed);
+      getcpu_fn_.store(&GetCPUViaSyscall, std::memory_order_relaxed);
+      return nullptr;
+    }
+    int fd = open("/proc/self/auxv", O_RDONLY);
+    if (fd == -1) {
+      // Kernel too old to have a VDSO.
+      vdso_base_.store(nullptr, std::memory_order_relaxed);
+      getcpu_fn_.store(&GetCPUViaSyscall, std::memory_order_relaxed);
+      return nullptr;
+    }
+    ElfW(auxv_t) aux;
+    while (read(fd, &aux, sizeof(aux)) == sizeof(aux)) {
+      if (aux.a_type == AT_SYSINFO_EHDR) {
+        vdso_base_.store(reinterpret_cast<void *>(aux.a_un.a_val),
+                         std::memory_order_relaxed);
+        break;
+      }
+    }
+    close(fd);
+    if (vdso_base_.load(std::memory_order_relaxed) == kInvalidBase) {
+      // Didn't find AT_SYSINFO_EHDR in auxv[].
+      vdso_base_.store(nullptr, std::memory_order_relaxed);
+    }
+  }
+  GetCpuFn fn = &GetCPUViaSyscall;  // default if VDSO not present.
+  if (vdso_base_.load(std::memory_order_relaxed)) {
+    VDSOSupport vdso;
+    SymbolInfo info;
+    if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) {
+      fn = reinterpret_cast<GetCpuFn>(const_cast<void *>(info.address));
+    }
+  }
+  // Subtle: this code runs outside of any locks; prevent compiler
+  // from assigning to getcpu_fn_ more than once.
+  getcpu_fn_.store(fn, std::memory_order_relaxed);
+  return vdso_base_.load(std::memory_order_relaxed);
+}
+
+const void *VDSOSupport::SetBase(const void *base) {
+  ABSL_RAW_CHECK(base != debugging_internal::ElfMemImage::kInvalidBase,
+                 "internal error");
+  const void *old_base = vdso_base_.load(std::memory_order_relaxed);
+  vdso_base_.store(base, std::memory_order_relaxed);
+  image_.Init(base);
+  // Also reset getcpu_fn_, so GetCPU could be tested with simulated VDSO.
+  getcpu_fn_.store(&InitAndGetCPU, std::memory_order_relaxed);
+  return old_base;
+}
+
+bool VDSOSupport::LookupSymbol(const char *name,
+                               const char *version,
+                               int type,
+                               SymbolInfo *info) const {
+  return image_.LookupSymbol(name, version, type, info);
+}
+
+bool VDSOSupport::LookupSymbolByAddress(const void *address,
+                                        SymbolInfo *info_out) const {
+  return image_.LookupSymbolByAddress(address, info_out);
+}
+
+// NOLINT on 'long' because this routine mimics kernel api.
+long VDSOSupport::GetCPUViaSyscall(unsigned *cpu,  // NOLINT(runtime/int)
+                                   void *, void *) {
+#ifdef SYS_getcpu
+  return syscall(SYS_getcpu, cpu, nullptr, nullptr);
+#else
+  // x86_64 never implemented sys_getcpu(), except as a VDSO call.
+  static_cast<void>(cpu);  // Avoid an unused argument compiler warning.
+  errno = ENOSYS;
+  return -1;
+#endif
+}
+
+// Use fast __vdso_getcpu if available.
+long VDSOSupport::InitAndGetCPU(unsigned *cpu,  // NOLINT(runtime/int)
+                                void *x, void *y) {
+  Init();
+  GetCpuFn fn = getcpu_fn_.load(std::memory_order_relaxed);
+  ABSL_RAW_CHECK(fn != &InitAndGetCPU, "Init() did not set getcpu_fn_");
+  return (*fn)(cpu, x, y);
+}
+
+// This function must be very fast, and may be called from very
+// low level (e.g. tcmalloc). Hence I avoid things like
+// GoogleOnceInit() and ::operator new.
+ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY
+int GetCPU() {
+  unsigned cpu;
+  int ret_code = (*VDSOSupport::getcpu_fn_)(&cpu, nullptr, nullptr);
+  return ret_code == 0 ? cpu : ret_code;
+}
+
+// We need to make sure VDSOSupport::Init() is called before
+// InitGoogle() does any setuid or chroot calls.  If VDSOSupport
+// is used in any global constructor, this will happen, since
+// VDSOSupport's constructor calls Init.  But if not, we need to
+// ensure it here, with a global constructor of our own.  This
+// is an allowed exception to the normal rule against non-trivial
+// global constructors.
+static class VDSOInitHelper {
+ public:
+  VDSOInitHelper() { VDSOSupport::Init(); }
+} vdso_init_helper;
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_HAVE_VDSO_SUPPORT
diff --git a/third_party/abseil_cpp/absl/debugging/internal/vdso_support.h b/third_party/abseil_cpp/absl/debugging/internal/vdso_support.h
new file mode 100644
index 000000000000..6562c6c2350a
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/internal/vdso_support.h
@@ -0,0 +1,158 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// Allow dynamic symbol lookup in the kernel VDSO page.
+//
+// VDSO stands for "Virtual Dynamic Shared Object" -- a page of
+// executable code, which looks like a shared library, but doesn't
+// necessarily exist anywhere on disk, and which gets mmap()ed into
+// every process by kernels which support VDSO, such as 2.6.x for 32-bit
+// executables, and 2.6.24 and above for 64-bit executables.
+//
+// More details could be found here:
+// http://www.trilithium.com/johan/2005/08/linux-gate/
+//
+// VDSOSupport -- a class representing kernel VDSO (if present).
+//
+// Example usage:
+//  VDSOSupport vdso;
+//  VDSOSupport::SymbolInfo info;
+//  typedef (*FN)(unsigned *, void *, void *);
+//  FN fn = nullptr;
+//  if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) {
+//     fn = reinterpret_cast<FN>(info.address);
+//  }
+
+#ifndef ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_
+#define ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/debugging/internal/elf_mem_image.h"
+
+#ifdef ABSL_HAVE_ELF_MEM_IMAGE
+
+#ifdef ABSL_HAVE_VDSO_SUPPORT
+#error ABSL_HAVE_VDSO_SUPPORT cannot be directly set
+#else
+#define ABSL_HAVE_VDSO_SUPPORT 1
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace debugging_internal {
+
+// NOTE: this class may be used from within tcmalloc, and can not
+// use any memory allocation routines.
+class VDSOSupport {
+ public:
+  VDSOSupport();
+
+  typedef ElfMemImage::SymbolInfo SymbolInfo;
+  typedef ElfMemImage::SymbolIterator SymbolIterator;
+
+  // On PowerPC64 VDSO symbols can either be of type STT_FUNC or STT_NOTYPE
+  // depending on how the kernel is built.  The kernel is normally built with
+  // STT_NOTYPE type VDSO symbols.  Let's make things simpler first by using a
+  // compile-time constant.
+#ifdef __powerpc64__
+  enum { kVDSOSymbolType = STT_NOTYPE };
+#else
+  enum { kVDSOSymbolType = STT_FUNC };
+#endif
+
+  // Answers whether we have a vdso at all.
+  bool IsPresent() const { return image_.IsPresent(); }
+
+  // Allow to iterate over all VDSO symbols.
+  SymbolIterator begin() const { return image_.begin(); }
+  SymbolIterator end() const { return image_.end(); }
+
+  // Look up versioned dynamic symbol in the kernel VDSO.
+  // Returns false if VDSO is not present, or doesn't contain given
+  // symbol/version/type combination.
+  // If info_out != nullptr, additional details are filled in.
+  bool LookupSymbol(const char *name, const char *version,
+                    int symbol_type, SymbolInfo *info_out) const;
+
+  // Find info about symbol (if any) which overlaps given address.
+  // Returns true if symbol was found; false if VDSO isn't present
+  // or doesn't have a symbol overlapping given address.
+  // If info_out != nullptr, additional details are filled in.
+  bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
+
+  // Used only for testing. Replace real VDSO base with a mock.
+  // Returns previous value of vdso_base_. After you are done testing,
+  // you are expected to call SetBase() with previous value, in order to
+  // reset state to the way it was.
+  const void *SetBase(const void *s);
+
+  // Computes vdso_base_ and returns it. Should be called as early as
+  // possible; before any thread creation, chroot or setuid.
+  static const void *Init();
+
+ private:
+  // image_ represents VDSO ELF image in memory.
+  // image_.ehdr_ == nullptr implies there is no VDSO.
+  ElfMemImage image_;
+
+  // Cached value of auxv AT_SYSINFO_EHDR, computed once.
+  // This is a tri-state:
+  //   kInvalidBase   => value hasn't been determined yet.
+  //              0   => there is no VDSO.
+  //           else   => vma of VDSO Elf{32,64}_Ehdr.
+  //
+  // When testing with mock VDSO, low bit is set.
+  // The low bit is always available because vdso_base_ is
+  // page-aligned.
+  static std::atomic<const void *> vdso_base_;
+
+  // NOLINT on 'long' because these routines mimic kernel api.
+  // The 'cache' parameter may be used by some versions of the kernel,
+  // and should be nullptr or point to a static buffer containing at
+  // least two 'long's.
+  static long InitAndGetCPU(unsigned *cpu, void *cache,     // NOLINT 'long'.
+                            void *unused);
+  static long GetCPUViaSyscall(unsigned *cpu, void *cache,  // NOLINT 'long'.
+                               void *unused);
+  typedef long (*GetCpuFn)(unsigned *cpu, void *cache,      // NOLINT 'long'.
+                           void *unused);
+
+  // This function pointer may point to InitAndGetCPU,
+  // GetCPUViaSyscall, or __vdso_getcpu at different stages of initialization.
+  ABSL_CONST_INIT static std::atomic<GetCpuFn> getcpu_fn_;
+
+  friend int GetCPU(void);  // Needs access to getcpu_fn_.
+
+  VDSOSupport(const VDSOSupport&) = delete;
+  VDSOSupport& operator=(const VDSOSupport&) = delete;
+};
+
+// Same as sched_getcpu() on later glibc versions.
+// Return current CPU, using (fast) __vdso_getcpu@LINUX_2.6 if present,
+// otherwise use syscall(SYS_getcpu,...).
+// May return -1 with errno == ENOSYS if the kernel doesn't
+// support SYS_getcpu.
+int GetCPU();
+
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_HAVE_ELF_MEM_IMAGE
+
+#endif  // ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_
diff --git a/third_party/abseil_cpp/absl/debugging/leak_check.cc b/third_party/abseil_cpp/absl/debugging/leak_check.cc
new file mode 100644
index 000000000000..ff9049559d4d
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/leak_check.cc
@@ -0,0 +1,53 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Wrappers around lsan_interface functions.
+// When lsan is not linked in, these functions are not available,
+// therefore Abseil code which depends on these functions is conditioned on the
+// definition of LEAK_SANITIZER.
+#include "absl/debugging/leak_check.h"
+
+#ifndef LEAK_SANITIZER
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+bool HaveLeakSanitizer() { return false; }
+void DoIgnoreLeak(const void*) { }
+void RegisterLivePointers(const void*, size_t) { }
+void UnRegisterLivePointers(const void*, size_t) { }
+LeakCheckDisabler::LeakCheckDisabler() { }
+LeakCheckDisabler::~LeakCheckDisabler() { }
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else
+
+#include <sanitizer/lsan_interface.h>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+bool HaveLeakSanitizer() { return true; }
+void DoIgnoreLeak(const void* ptr) { __lsan_ignore_object(ptr); }
+void RegisterLivePointers(const void* ptr, size_t size) {
+  __lsan_register_root_region(ptr, size);
+}
+void UnRegisterLivePointers(const void* ptr, size_t size) {
+  __lsan_unregister_root_region(ptr, size);
+}
+LeakCheckDisabler::LeakCheckDisabler() { __lsan_disable(); }
+LeakCheckDisabler::~LeakCheckDisabler() { __lsan_enable(); }
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // LEAK_SANITIZER
diff --git a/third_party/abseil_cpp/absl/debugging/leak_check.h b/third_party/abseil_cpp/absl/debugging/leak_check.h
new file mode 100644
index 000000000000..7a5a22dd1caf
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/leak_check.h
@@ -0,0 +1,113 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: leak_check.h
+// -----------------------------------------------------------------------------
+//
+// This file contains functions that affect leak checking behavior within
+// targets built with the LeakSanitizer (LSan), a memory leak detector that is
+// integrated within the AddressSanitizer (ASan) as an additional component, or
+// which can be used standalone. LSan and ASan are included (or can be provided)
+// as additional components for most compilers such as Clang, gcc and MSVC.
+// Note: this leak checking API is not yet supported in MSVC.
+// Leak checking is enabled by default in all ASan builds.
+//
+// See https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer
+//
+// -----------------------------------------------------------------------------
+#ifndef ABSL_DEBUGGING_LEAK_CHECK_H_
+#define ABSL_DEBUGGING_LEAK_CHECK_H_
+
+#include <cstddef>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// HaveLeakSanitizer()
+//
+// Returns true if a leak-checking sanitizer (either ASan or standalone LSan) is
+// currently built into this target.
+bool HaveLeakSanitizer();
+
+// DoIgnoreLeak()
+//
+// Implements `IgnoreLeak()` below. This function should usually
+// not be called directly; calling `IgnoreLeak()` is preferred.
+void DoIgnoreLeak(const void* ptr);
+
+// IgnoreLeak()
+//
+// Instruct the leak sanitizer to ignore leak warnings on the object referenced
+// by the passed pointer, as well as all heap objects transitively referenced
+// by it. The passed object pointer can point to either the beginning of the
+// object or anywhere within it.
+//
+// Example:
+//
+//   static T* obj = IgnoreLeak(new T(...));
+//
+// If the passed `ptr` does not point to an actively allocated object at the
+// time `IgnoreLeak()` is called, the call is a no-op; if it is actively
+// allocated, the object must not get deallocated later.
+//
+template <typename T>
+T* IgnoreLeak(T* ptr) {
+  DoIgnoreLeak(ptr);
+  return ptr;
+}
+
+// LeakCheckDisabler
+//
+// This helper class indicates that any heap allocations done in the code block
+// covered by the scoped object, which should be allocated on the stack, will
+// not be reported as leaks. Leak check disabling will occur within the code
+// block and any nested function calls within the code block.
+//
+// Example:
+//
+//   void Foo() {
+//     LeakCheckDisabler disabler;
+//     ... code that allocates objects whose leaks should be ignored ...
+//   }
+//
+// REQUIRES: Destructor runs in same thread as constructor
+class LeakCheckDisabler {
+ public:
+  LeakCheckDisabler();
+  LeakCheckDisabler(const LeakCheckDisabler&) = delete;
+  LeakCheckDisabler& operator=(const LeakCheckDisabler&) = delete;
+  ~LeakCheckDisabler();
+};
+
+// RegisterLivePointers()
+//
+// Registers `ptr[0,size-1]` as pointers to memory that is still actively being
+// referenced and for which leak checking should be ignored. This function is
+// useful if you store pointers in mapped memory, for memory ranges that we know
+// are correct but for which normal analysis would flag as leaked code.
+void RegisterLivePointers(const void* ptr, size_t size);
+
+// UnRegisterLivePointers()
+//
+// Deregisters the pointers previously marked as active in
+// `RegisterLivePointers()`, enabling leak checking of those pointers.
+void UnRegisterLivePointers(const void* ptr, size_t size);
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_LEAK_CHECK_H_
diff --git a/third_party/abseil_cpp/absl/debugging/leak_check_disable.cc b/third_party/abseil_cpp/absl/debugging/leak_check_disable.cc
new file mode 100644
index 000000000000..924d6e3d543b
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/leak_check_disable.cc
@@ -0,0 +1,20 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Disable LeakSanitizer when this file is linked in.
+// This function overrides __lsan_is_turned_off from sanitizer/lsan_interface.h
+extern "C" int __lsan_is_turned_off();
+extern "C" int __lsan_is_turned_off() {
+  return 1;
+}
diff --git a/third_party/abseil_cpp/absl/debugging/leak_check_fail_test.cc b/third_party/abseil_cpp/absl/debugging/leak_check_fail_test.cc
new file mode 100644
index 000000000000..c49b81a9d9e2
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/leak_check_fail_test.cc
@@ -0,0 +1,41 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <memory>
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/debugging/leak_check.h"
+
+namespace {
+
+TEST(LeakCheckTest, LeakMemory) {
+  // This test is expected to cause lsan failures on program exit. Therefore the
+  // test will be run only by leak_check_test.sh, which will verify a
+  // failed exit code.
+
+  char* foo = strdup("lsan should complain about this leaked string");
+  ABSL_RAW_LOG(INFO, "Should detect leaked string %s", foo);
+}
+
+TEST(LeakCheckTest, LeakMemoryAfterDisablerScope) {
+  // This test is expected to cause lsan failures on program exit. Therefore the
+  // test will be run only by external_leak_check_test.sh, which will verify a
+  // failed exit code.
+  { absl::LeakCheckDisabler disabler; }
+  char* foo = strdup("lsan should also complain about this leaked string");
+  ABSL_RAW_LOG(INFO, "Re-enabled leak detection.Should detect leaked string %s",
+               foo);
+}
+
+}  // namespace
diff --git a/third_party/abseil_cpp/absl/debugging/leak_check_test.cc b/third_party/abseil_cpp/absl/debugging/leak_check_test.cc
new file mode 100644
index 000000000000..b5cc4874880f
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/leak_check_test.cc
@@ -0,0 +1,42 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <string>
+
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/debugging/leak_check.h"
+
+namespace {
+
+TEST(LeakCheckTest, DetectLeakSanitizer) {
+#ifdef ABSL_EXPECT_LEAK_SANITIZER
+  EXPECT_TRUE(absl::HaveLeakSanitizer());
+#else
+  EXPECT_FALSE(absl::HaveLeakSanitizer());
+#endif
+}
+
+TEST(LeakCheckTest, IgnoreLeakSuppressesLeakedMemoryErrors) {
+  auto foo = absl::IgnoreLeak(new std::string("some ignored leaked string"));
+  ABSL_RAW_LOG(INFO, "Ignoring leaked string %s", foo->c_str());
+}
+
+TEST(LeakCheckTest, LeakCheckDisablerIgnoresLeak) {
+  absl::LeakCheckDisabler disabler;
+  auto foo = new std::string("some string leaked while checks are disabled");
+  ABSL_RAW_LOG(INFO, "Ignoring leaked string %s", foo->c_str());
+}
+
+}  // namespace
diff --git a/third_party/abseil_cpp/absl/debugging/stacktrace.cc b/third_party/abseil_cpp/absl/debugging/stacktrace.cc
new file mode 100644
index 000000000000..1f7c7d82b2d2
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/stacktrace.cc
@@ -0,0 +1,140 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Produce stack trace.
+//
+// There are three different ways we can try to get the stack trace:
+//
+// 1) Our hand-coded stack-unwinder.  This depends on a certain stack
+//    layout, which is used by gcc (and those systems using a
+//    gcc-compatible ABI) on x86 systems, at least since gcc 2.95.
+//    It uses the frame pointer to do its work.
+//
+// 2) The libunwind library.  This is still in development, and as a
+//    separate library adds a new dependency, but doesn't need a frame
+//    pointer.  It also doesn't call malloc.
+//
+// 3) The gdb unwinder -- also the one used by the c++ exception code.
+//    It's obviously well-tested, but has a fatal flaw: it can call
+//    malloc() from the unwinder.  This is a problem because we're
+//    trying to use the unwinder to instrument malloc().
+//
+// Note: if you add a new implementation here, make sure it works
+// correctly when absl::GetStackTrace() is called with max_depth == 0.
+// Some code may do that.
+
+#include "absl/debugging/stacktrace.h"
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/base/port.h"
+#include "absl/debugging/internal/stacktrace_config.h"
+
+#if defined(ABSL_STACKTRACE_INL_HEADER)
+#include ABSL_STACKTRACE_INL_HEADER
+#else
+# error Cannot calculate stack trace: will need to write for your environment
+
+# include "absl/debugging/internal/stacktrace_aarch64-inl.inc"
+# include "absl/debugging/internal/stacktrace_arm-inl.inc"
+# include "absl/debugging/internal/stacktrace_generic-inl.inc"
+# include "absl/debugging/internal/stacktrace_powerpc-inl.inc"
+# include "absl/debugging/internal/stacktrace_unimplemented-inl.inc"
+# include "absl/debugging/internal/stacktrace_win32-inl.inc"
+# include "absl/debugging/internal/stacktrace_x86-inl.inc"
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace {
+
+typedef int (*Unwinder)(void**, int*, int, int, const void*, int*);
+std::atomic<Unwinder> custom;
+
+template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
+ABSL_ATTRIBUTE_ALWAYS_INLINE inline int Unwind(void** result, int* sizes,
+                                               int max_depth, int skip_count,
+                                               const void* uc,
+                                               int* min_dropped_frames) {
+  Unwinder f = &UnwindImpl<IS_STACK_FRAMES, IS_WITH_CONTEXT>;
+  Unwinder g = custom.load(std::memory_order_acquire);
+  if (g != nullptr) f = g;
+
+  // Add 1 to skip count for the unwinder function itself
+  int size = (*f)(result, sizes, max_depth, skip_count + 1, uc,
+                  min_dropped_frames);
+  // To disable tail call to (*f)(...)
+  ABSL_BLOCK_TAIL_CALL_OPTIMIZATION();
+  return size;
+}
+
+}  // anonymous namespace
+
+ABSL_ATTRIBUTE_NOINLINE ABSL_ATTRIBUTE_NO_TAIL_CALL int GetStackFrames(
+    void** result, int* sizes, int max_depth, int skip_count) {
+  return Unwind<true, false>(result, sizes, max_depth, skip_count, nullptr,
+                             nullptr);
+}
+
+ABSL_ATTRIBUTE_NOINLINE ABSL_ATTRIBUTE_NO_TAIL_CALL int
+GetStackFramesWithContext(void** result, int* sizes, int max_depth,
+                          int skip_count, const void* uc,
+                          int* min_dropped_frames) {
+  return Unwind<true, true>(result, sizes, max_depth, skip_count, uc,
+                            min_dropped_frames);
+}
+
+ABSL_ATTRIBUTE_NOINLINE ABSL_ATTRIBUTE_NO_TAIL_CALL int GetStackTrace(
+    void** result, int max_depth, int skip_count) {
+  return Unwind<false, false>(result, nullptr, max_depth, skip_count, nullptr,
+                              nullptr);
+}
+
+ABSL_ATTRIBUTE_NOINLINE ABSL_ATTRIBUTE_NO_TAIL_CALL int
+GetStackTraceWithContext(void** result, int max_depth, int skip_count,
+                         const void* uc, int* min_dropped_frames) {
+  return Unwind<false, true>(result, nullptr, max_depth, skip_count, uc,
+                             min_dropped_frames);
+}
+
+void SetStackUnwinder(Unwinder w) {
+  custom.store(w, std::memory_order_release);
+}
+
+int DefaultStackUnwinder(void** pcs, int* sizes, int depth, int skip,
+                         const void* uc, int* min_dropped_frames) {
+  skip++;  // For this function
+  Unwinder f = nullptr;
+  if (sizes == nullptr) {
+    if (uc == nullptr) {
+      f = &UnwindImpl<false, false>;
+    } else {
+      f = &UnwindImpl<false, true>;
+    }
+  } else {
+    if (uc == nullptr) {
+      f = &UnwindImpl<true, false>;
+    } else {
+      f = &UnwindImpl<true, true>;
+    }
+  }
+  volatile int x = 0;
+  int n = (*f)(pcs, sizes, depth, skip, uc, min_dropped_frames);
+  x = 1; (void) x;  // To disable tail call to (*f)(...)
+  return n;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/stacktrace.h b/third_party/abseil_cpp/absl/debugging/stacktrace.h
new file mode 100644
index 000000000000..0ec0ffdabd42
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/stacktrace.h
@@ -0,0 +1,231 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: stacktrace.h
+// -----------------------------------------------------------------------------
+//
+// This file contains routines to extract the current stack trace and associated
+// stack frames. These functions are thread-safe and async-signal-safe.
+//
+// Note that stack trace functionality is platform dependent and requires
+// additional support from the compiler/build system in most cases. (That is,
+// this functionality generally only works on platforms/builds that have been
+// specifically configured to support it.)
+//
+// Note: stack traces in Abseil that do not utilize a symbolizer will result in
+// frames consisting of function addresses rather than human-readable function
+// names. (See symbolize.h for information on symbolizing these values.)
+
+#ifndef ABSL_DEBUGGING_STACKTRACE_H_
+#define ABSL_DEBUGGING_STACKTRACE_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// GetStackFrames()
+//
+// Records program counter values for up to `max_depth` frames, skipping the
+// most recent `skip_count` stack frames, stores their corresponding values
+// and sizes in `results` and `sizes` buffers, and returns the number of frames
+// stored. (Note that the frame generated for the `absl::GetStackFrames()`
+// routine itself is also skipped.)
+//
+// Example:
+//
+//      main() { foo(); }
+//      foo() { bar(); }
+//      bar() {
+//        void* result[10];
+//        int sizes[10];
+//        int depth = absl::GetStackFrames(result, sizes, 10, 1);
+//      }
+//
+// The current stack frame would consist of three function calls: `bar()`,
+// `foo()`, and then `main()`; however, since the `GetStackFrames()` call sets
+// `skip_count` to `1`, it will skip the frame for `bar()`, the most recently
+// invoked function call. It will therefore return 2 and fill `result` with
+// program counters within the following functions:
+//
+//      result[0]       foo()
+//      result[1]       main()
+//
+// (Note: in practice, a few more entries after `main()` may be added to account
+// for startup processes.)
+//
+// Corresponding stack frame sizes will also be recorded:
+//
+//    sizes[0]       16
+//    sizes[1]       16
+//
+// (Stack frame sizes of `16` above are just for illustration purposes.)
+//
+// Stack frame sizes of 0 or less indicate that those frame sizes couldn't
+// be identified.
+//
+// This routine may return fewer stack frame entries than are
+// available. Also note that `result` and `sizes` must both be non-null.
+extern int GetStackFrames(void** result, int* sizes, int max_depth,
+                          int skip_count);
+
+// GetStackFramesWithContext()
+//
+// Records program counter values obtained from a signal handler. Records
+// program counter values for up to `max_depth` frames, skipping the most recent
+// `skip_count` stack frames, stores their corresponding values and sizes in
+// `results` and `sizes` buffers, and returns the number of frames stored. (Note
+// that the frame generated for the `absl::GetStackFramesWithContext()` routine
+// itself is also skipped.)
+//
+// The `uc` parameter, if non-null, should be a pointer to a `ucontext_t` value
+// passed to a signal handler registered via the `sa_sigaction` field of a
+// `sigaction` struct. (See
+// http://man7.org/linux/man-pages/man2/sigaction.2.html.) The `uc` value may
+// help a stack unwinder to provide a better stack trace under certain
+// conditions. `uc` may safely be null.
+//
+// The `min_dropped_frames` output parameter, if non-null, points to the
+// location to note any dropped stack frames, if any, due to buffer limitations
+// or other reasons. (This value will be set to `0` if no frames were dropped.)
+// The number of total stack frames is guaranteed to be >= skip_count +
+// max_depth + *min_dropped_frames.
+extern int GetStackFramesWithContext(void** result, int* sizes, int max_depth,
+                                     int skip_count, const void* uc,
+                                     int* min_dropped_frames);
+
+// GetStackTrace()
+//
+// Records program counter values for up to `max_depth` frames, skipping the
+// most recent `skip_count` stack frames, stores their corresponding values
+// in `results`, and returns the number of frames
+// stored. Note that this function is similar to `absl::GetStackFrames()`
+// except that it returns the stack trace only, and not stack frame sizes.
+//
+// Example:
+//
+//      main() { foo(); }
+//      foo() { bar(); }
+//      bar() {
+//        void* result[10];
+//        int depth = absl::GetStackTrace(result, 10, 1);
+//      }
+//
+// This produces:
+//
+//      result[0]       foo
+//      result[1]       main
+//           ....       ...
+//
+// `result` must not be null.
+extern int GetStackTrace(void** result, int max_depth, int skip_count);
+
+// GetStackTraceWithContext()
+//
+// Records program counter values obtained from a signal handler. Records
+// program counter values for up to `max_depth` frames, skipping the most recent
+// `skip_count` stack frames, stores their corresponding values in `results`,
+// and returns the number of frames stored. (Note that the frame generated for
+// the `absl::GetStackFramesWithContext()` routine itself is also skipped.)
+//
+// The `uc` parameter, if non-null, should be a pointer to a `ucontext_t` value
+// passed to a signal handler registered via the `sa_sigaction` field of a
+// `sigaction` struct. (See
+// http://man7.org/linux/man-pages/man2/sigaction.2.html.) The `uc` value may
+// help a stack unwinder to provide a better stack trace under certain
+// conditions. `uc` may safely be null.
+//
+// The `min_dropped_frames` output parameter, if non-null, points to the
+// location to note any dropped stack frames, if any, due to buffer limitations
+// or other reasons. (This value will be set to `0` if no frames were dropped.)
+// The number of total stack frames is guaranteed to be >= skip_count +
+// max_depth + *min_dropped_frames.
+extern int GetStackTraceWithContext(void** result, int max_depth,
+                                    int skip_count, const void* uc,
+                                    int* min_dropped_frames);
+
+// SetStackUnwinder()
+//
+// Provides a custom function for unwinding stack frames that will be used in
+// place of the default stack unwinder when invoking the static
+// GetStack{Frames,Trace}{,WithContext}() functions above.
+//
+// The arguments passed to the unwinder function will match the
+// arguments passed to `absl::GetStackFramesWithContext()` except that sizes
+// will be non-null iff the caller is interested in frame sizes.
+//
+// If unwinder is set to null, we revert to the default stack-tracing behavior.
+//
+// *****************************************************************************
+// WARNING
+// *****************************************************************************
+//
+// absl::SetStackUnwinder is not suitable for general purpose use.  It is
+// provided for custom runtimes.
+// Some things to watch out for when calling `absl::SetStackUnwinder()`:
+//
+// (a) The unwinder may be called from within signal handlers and
+// therefore must be async-signal-safe.
+//
+// (b) Even after a custom stack unwinder has been unregistered, other
+// threads may still be in the process of using that unwinder.
+// Therefore do not clean up any state that may be needed by an old
+// unwinder.
+// *****************************************************************************
+extern void SetStackUnwinder(int (*unwinder)(void** pcs, int* sizes,
+                                             int max_depth, int skip_count,
+                                             const void* uc,
+                                             int* min_dropped_frames));
+
+// DefaultStackUnwinder()
+//
+// Records program counter values of up to `max_depth` frames, skipping the most
+// recent `skip_count` stack frames, and stores their corresponding values in
+// `pcs`. (Note that the frame generated for this call itself is also skipped.)
+// This function acts as a generic stack-unwinder; prefer usage of the more
+// specific `GetStack{Trace,Frames}{,WithContext}()` functions above.
+//
+// If you have set your own stack unwinder (with the `SetStackUnwinder()`
+// function above, you can still get the default stack unwinder by calling
+// `DefaultStackUnwinder()`, which will ignore any previously set stack unwinder
+// and use the default one instead.
+//
+// Because this function is generic, only `pcs` is guaranteed to be non-null
+// upon return. It is legal for `sizes`, `uc`, and `min_dropped_frames` to all
+// be null when called.
+//
+// The semantics are the same as the corresponding `GetStack*()` function in the
+// case where `absl::SetStackUnwinder()` was never called. Equivalents are:
+//
+//                       null sizes         |        non-nullptr sizes
+//             |==========================================================|
+//     null uc | GetStackTrace()            | GetStackFrames()            |
+// non-null uc | GetStackTraceWithContext() | GetStackFramesWithContext() |
+//             |==========================================================|
+extern int DefaultStackUnwinder(void** pcs, int* sizes, int max_depth,
+                                int skip_count, const void* uc,
+                                int* min_dropped_frames);
+
+namespace debugging_internal {
+// Returns true for platforms which are expected to have functioning stack trace
+// implementations. Intended to be used for tests which want to exclude
+// verification of logic known to be broken because stack traces are not
+// working.
+extern bool StackTraceWorksForTest();
+}  // namespace debugging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_STACKTRACE_H_
diff --git a/third_party/abseil_cpp/absl/debugging/symbolize.cc b/third_party/abseil_cpp/absl/debugging/symbolize.cc
new file mode 100644
index 000000000000..54ed97002a1c
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/symbolize.cc
@@ -0,0 +1,25 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/debugging/symbolize.h"
+
+#if defined(ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE)
+#include "absl/debugging/symbolize_elf.inc"
+#elif defined(_WIN32)
+// The Windows Symbolizer only works if PDB files containing the debug info
+// are available to the program at runtime.
+#include "absl/debugging/symbolize_win32.inc"
+#else
+#include "absl/debugging/symbolize_unimplemented.inc"
+#endif
diff --git a/third_party/abseil_cpp/absl/debugging/symbolize.h b/third_party/abseil_cpp/absl/debugging/symbolize.h
new file mode 100644
index 000000000000..43d93a86822e
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/symbolize.h
@@ -0,0 +1,99 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: symbolize.h
+// -----------------------------------------------------------------------------
+//
+// This file configures the Abseil symbolizer for use in converting instruction
+// pointer addresses (program counters) into human-readable names (function
+// calls, etc.) within Abseil code.
+//
+// The symbolizer may be invoked from several sources:
+//
+//   * Implicitly, through the installation of an Abseil failure signal handler.
+//     (See failure_signal_handler.h for more information.)
+//   * By calling `Symbolize()` directly on a program counter you obtain through
+//     `absl::GetStackTrace()` or `absl::GetStackFrames()`. (See stacktrace.h
+//     for more information.
+//   * By calling `Symbolize()` directly on a program counter you obtain through
+//     other means (which would be platform-dependent).
+//
+// In all of the above cases, the symbolizer must first be initialized before
+// any program counter values can be symbolized. If you are installing a failure
+// signal handler, initialize the symbolizer before you do so.
+//
+// Example:
+//
+//   int main(int argc, char** argv) {
+//     // Initialize the Symbolizer before installing the failure signal handler
+//     absl::InitializeSymbolizer(argv[0]);
+//
+//     // Now you may install the failure signal handler
+//     absl::FailureSignalHandlerOptions options;
+//     absl::InstallFailureSignalHandler(options);
+//
+//     // Start running your main program
+//     ...
+//     return 0;
+//  }
+//
+#ifndef ABSL_DEBUGGING_SYMBOLIZE_H_
+#define ABSL_DEBUGGING_SYMBOLIZE_H_
+
+#include "absl/debugging/internal/symbolize.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// InitializeSymbolizer()
+//
+// Initializes the program counter symbolizer, given the path of the program
+// (typically obtained through `main()`s `argv[0]`). The Abseil symbolizer
+// allows you to read program counters (instruction pointer values) using their
+// human-readable names within output such as stack traces.
+//
+// Example:
+//
+// int main(int argc, char *argv[]) {
+//   absl::InitializeSymbolizer(argv[0]);
+//   // Now you can use the symbolizer
+// }
+void InitializeSymbolizer(const char* argv0);
+//
+// Symbolize()
+//
+// Symbolizes a program counter (instruction pointer value) `pc` and, on
+// success, writes the name to `out`. The symbol name is demangled, if possible.
+// Note that the symbolized name may be truncated and will be NUL-terminated.
+// Demangling is supported for symbols generated by GCC 3.x or newer). Returns
+// `false` on failure.
+//
+// Example:
+//
+//   // Print a program counter and its symbol name.
+//   static void DumpPCAndSymbol(void *pc) {
+//     char tmp[1024];
+//     const char *symbol = "(unknown)";
+//     if (absl::Symbolize(pc, tmp, sizeof(tmp))) {
+//       symbol = tmp;
+//     }
+//     absl::PrintF("%p  %s\n", pc, symbol);
+//  }
+bool Symbolize(const void *pc, char *out, int out_size);
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_DEBUGGING_SYMBOLIZE_H_
diff --git a/third_party/abseil_cpp/absl/debugging/symbolize_elf.inc b/third_party/abseil_cpp/absl/debugging/symbolize_elf.inc
new file mode 100644
index 000000000000..ec86f9a93327
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/symbolize_elf.inc
@@ -0,0 +1,1482 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This library provides Symbolize() function that symbolizes program
+// counters to their corresponding symbol names on linux platforms.
+// This library has a minimal implementation of an ELF symbol table
+// reader (i.e. it doesn't depend on libelf, etc.).
+//
+// The algorithm used in Symbolize() is as follows.
+//
+//   1. Go through a list of maps in /proc/self/maps and find the map
+//   containing the program counter.
+//
+//   2. Open the mapped file and find a regular symbol table inside.
+//   Iterate over symbols in the symbol table and look for the symbol
+//   containing the program counter.  If such a symbol is found,
+//   obtain the symbol name, and demangle the symbol if possible.
+//   If the symbol isn't found in the regular symbol table (binary is
+//   stripped), try the same thing with a dynamic symbol table.
+//
+// Note that Symbolize() is originally implemented to be used in
+// signal handlers, hence it doesn't use malloc() and other unsafe
+// operations.  It should be both thread-safe and async-signal-safe.
+//
+// Implementation note:
+//
+// We don't use heaps but only use stacks.  We want to reduce the
+// stack consumption so that the symbolizer can run on small stacks.
+//
+// Here are some numbers collected with GCC 4.1.0 on x86:
+// - sizeof(Elf32_Sym)  = 16
+// - sizeof(Elf32_Shdr) = 40
+// - sizeof(Elf64_Sym)  = 24
+// - sizeof(Elf64_Shdr) = 64
+//
+// This implementation is intended to be async-signal-safe but uses some
+// functions which are not guaranteed to be so, such as memchr() and
+// memmove().  We assume they are async-signal-safe.
+
+#include <dlfcn.h>
+#include <elf.h>
+#include <fcntl.h>
+#include <link.h>  // For ElfW() macro.
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <algorithm>
+#include <atomic>
+#include <cerrno>
+#include <cinttypes>
+#include <climits>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#include "absl/base/casts.h"
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/low_level_alloc.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/spinlock.h"
+#include "absl/base/port.h"
+#include "absl/debugging/internal/demangle.h"
+#include "absl/debugging/internal/vdso_support.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// Value of argv[0]. Used by MaybeInitializeObjFile().
+static char *argv0_value = nullptr;
+
+void InitializeSymbolizer(const char *argv0) {
+  if (argv0_value != nullptr) {
+    free(argv0_value);
+    argv0_value = nullptr;
+  }
+  if (argv0 != nullptr && argv0[0] != '\0') {
+    argv0_value = strdup(argv0);
+  }
+}
+
+namespace debugging_internal {
+namespace {
+
+// Re-runs fn until it doesn't cause EINTR.
+#define NO_INTR(fn) \
+  do {              \
+  } while ((fn) < 0 && errno == EINTR)
+
+// On Linux, ELF_ST_* are defined in <linux/elf.h>.  To make this portable
+// we define our own ELF_ST_BIND and ELF_ST_TYPE if not available.
+#ifndef ELF_ST_BIND
+#define ELF_ST_BIND(info) (((unsigned char)(info)) >> 4)
+#endif
+
+#ifndef ELF_ST_TYPE
+#define ELF_ST_TYPE(info) (((unsigned char)(info)) & 0xF)
+#endif
+
+// Some platforms use a special .opd section to store function pointers.
+const char kOpdSectionName[] = ".opd";
+
+#if (defined(__powerpc__) && !(_CALL_ELF > 1)) || defined(__ia64)
+// Use opd section for function descriptors on these platforms, the function
+// address is the first word of the descriptor.
+enum { kPlatformUsesOPDSections = 1 };
+#else  // not PPC or IA64
+enum { kPlatformUsesOPDSections = 0 };
+#endif
+
+// This works for PowerPC & IA64 only.  A function descriptor consist of two
+// pointers and the first one is the function's entry.
+const size_t kFunctionDescriptorSize = sizeof(void *) * 2;
+
+const int kMaxDecorators = 10;  // Seems like a reasonable upper limit.
+
+struct InstalledSymbolDecorator {
+  SymbolDecorator fn;
+  void *arg;
+  int ticket;
+};
+
+int g_num_decorators;
+InstalledSymbolDecorator g_decorators[kMaxDecorators];
+
+struct FileMappingHint {
+  const void *start;
+  const void *end;
+  uint64_t offset;
+  const char *filename;
+};
+
+// Protects g_decorators.
+// We are using SpinLock and not a Mutex here, because we may be called
+// from inside Mutex::Lock itself, and it prohibits recursive calls.
+// This happens in e.g. base/stacktrace_syscall_unittest.
+// Moreover, we are using only TryLock(), if the decorator list
+// is being modified (is busy), we skip all decorators, and possibly
+// loose some info. Sorry, that's the best we could do.
+ABSL_CONST_INIT absl::base_internal::SpinLock g_decorators_mu(
+    absl::kConstInit, absl::base_internal::SCHEDULE_KERNEL_ONLY);
+
+const int kMaxFileMappingHints = 8;
+int g_num_file_mapping_hints;
+FileMappingHint g_file_mapping_hints[kMaxFileMappingHints];
+// Protects g_file_mapping_hints.
+ABSL_CONST_INIT absl::base_internal::SpinLock g_file_mapping_mu(
+    absl::kConstInit, absl::base_internal::SCHEDULE_KERNEL_ONLY);
+
+// Async-signal-safe function to zero a buffer.
+// memset() is not guaranteed to be async-signal-safe.
+static void SafeMemZero(void* p, size_t size) {
+  unsigned char *c = static_cast<unsigned char *>(p);
+  while (size--) {
+    *c++ = 0;
+  }
+}
+
+struct ObjFile {
+  ObjFile()
+      : filename(nullptr),
+        start_addr(nullptr),
+        end_addr(nullptr),
+        offset(0),
+        fd(-1),
+        elf_type(-1) {
+    SafeMemZero(&elf_header, sizeof(elf_header));
+  }
+
+  char *filename;
+  const void *start_addr;
+  const void *end_addr;
+  uint64_t offset;
+
+  // The following fields are initialized on the first access to the
+  // object file.
+  int fd;
+  int elf_type;
+  ElfW(Ehdr) elf_header;
+};
+
+// Build 4-way associative cache for symbols. Within each cache line, symbols
+// are replaced in LRU order.
+enum {
+  ASSOCIATIVITY = 4,
+};
+struct SymbolCacheLine {
+  const void *pc[ASSOCIATIVITY];
+  char *name[ASSOCIATIVITY];
+
+  // age[i] is incremented when a line is accessed. it's reset to zero if the
+  // i'th entry is read.
+  uint32_t age[ASSOCIATIVITY];
+};
+
+// ---------------------------------------------------------------
+// An async-signal-safe arena for LowLevelAlloc
+static std::atomic<base_internal::LowLevelAlloc::Arena *> g_sig_safe_arena;
+
+static base_internal::LowLevelAlloc::Arena *SigSafeArena() {
+  return g_sig_safe_arena.load(std::memory_order_acquire);
+}
+
+static void InitSigSafeArena() {
+  if (SigSafeArena() == nullptr) {
+    base_internal::LowLevelAlloc::Arena *new_arena =
+        base_internal::LowLevelAlloc::NewArena(
+            base_internal::LowLevelAlloc::kAsyncSignalSafe);
+    base_internal::LowLevelAlloc::Arena *old_value = nullptr;
+    if (!g_sig_safe_arena.compare_exchange_strong(old_value, new_arena,
+                                                  std::memory_order_release,
+                                                  std::memory_order_relaxed)) {
+      // We lost a race to allocate an arena; deallocate.
+      base_internal::LowLevelAlloc::DeleteArena(new_arena);
+    }
+  }
+}
+
+// ---------------------------------------------------------------
+// An AddrMap is a vector of ObjFile, using SigSafeArena() for allocation.
+
+class AddrMap {
+ public:
+  AddrMap() : size_(0), allocated_(0), obj_(nullptr) {}
+  ~AddrMap() { base_internal::LowLevelAlloc::Free(obj_); }
+  int Size() const { return size_; }
+  ObjFile *At(int i) { return &obj_[i]; }
+  ObjFile *Add();
+  void Clear();
+
+ private:
+  int size_;       // count of valid elements (<= allocated_)
+  int allocated_;  // count of allocated elements
+  ObjFile *obj_;   // array of allocated_ elements
+  AddrMap(const AddrMap &) = delete;
+  AddrMap &operator=(const AddrMap &) = delete;
+};
+
+void AddrMap::Clear() {
+  for (int i = 0; i != size_; i++) {
+    At(i)->~ObjFile();
+  }
+  size_ = 0;
+}
+
+ObjFile *AddrMap::Add() {
+  if (size_ == allocated_) {
+    int new_allocated = allocated_ * 2 + 50;
+    ObjFile *new_obj_ =
+        static_cast<ObjFile *>(base_internal::LowLevelAlloc::AllocWithArena(
+            new_allocated * sizeof(*new_obj_), SigSafeArena()));
+    if (obj_) {
+      memcpy(new_obj_, obj_, allocated_ * sizeof(*new_obj_));
+      base_internal::LowLevelAlloc::Free(obj_);
+    }
+    obj_ = new_obj_;
+    allocated_ = new_allocated;
+  }
+  return new (&obj_[size_++]) ObjFile;
+}
+
+// ---------------------------------------------------------------
+
+enum FindSymbolResult { SYMBOL_NOT_FOUND = 1, SYMBOL_TRUNCATED, SYMBOL_FOUND };
+
+class Symbolizer {
+ public:
+  Symbolizer();
+  ~Symbolizer();
+  const char *GetSymbol(const void *const pc);
+
+ private:
+  char *CopyString(const char *s) {
+    int len = strlen(s);
+    char *dst = static_cast<char *>(
+        base_internal::LowLevelAlloc::AllocWithArena(len + 1, SigSafeArena()));
+    ABSL_RAW_CHECK(dst != nullptr, "out of memory");
+    memcpy(dst, s, len + 1);
+    return dst;
+  }
+  ObjFile *FindObjFile(const void *const start,
+                       size_t size) ABSL_ATTRIBUTE_NOINLINE;
+  static bool RegisterObjFile(const char *filename,
+                              const void *const start_addr,
+                              const void *const end_addr, uint64_t offset,
+                              void *arg);
+  SymbolCacheLine *GetCacheLine(const void *const pc);
+  const char *FindSymbolInCache(const void *const pc);
+  const char *InsertSymbolInCache(const void *const pc, const char *name);
+  void AgeSymbols(SymbolCacheLine *line);
+  void ClearAddrMap();
+  FindSymbolResult GetSymbolFromObjectFile(const ObjFile &obj,
+                                           const void *const pc,
+                                           const ptrdiff_t relocation,
+                                           char *out, int out_size,
+                                           char *tmp_buf, int tmp_buf_size);
+
+  enum {
+    SYMBOL_BUF_SIZE = 3072,
+    TMP_BUF_SIZE = 1024,
+    SYMBOL_CACHE_LINES = 128,
+  };
+
+  AddrMap addr_map_;
+
+  bool ok_;
+  bool addr_map_read_;
+
+  char symbol_buf_[SYMBOL_BUF_SIZE];
+
+  // tmp_buf_ will be used to store arrays of ElfW(Shdr) and ElfW(Sym)
+  // so we ensure that tmp_buf_ is properly aligned to store either.
+  alignas(16) char tmp_buf_[TMP_BUF_SIZE];
+  static_assert(alignof(ElfW(Shdr)) <= 16,
+                "alignment of tmp buf too small for Shdr");
+  static_assert(alignof(ElfW(Sym)) <= 16,
+                "alignment of tmp buf too small for Sym");
+
+  SymbolCacheLine symbol_cache_[SYMBOL_CACHE_LINES];
+};
+
+static std::atomic<Symbolizer *> g_cached_symbolizer;
+
+}  // namespace
+
+static int SymbolizerSize() {
+#if defined(__wasm__) || defined(__asmjs__)
+  int pagesize = getpagesize();
+#else
+  int pagesize = sysconf(_SC_PAGESIZE);
+#endif
+  return ((sizeof(Symbolizer) - 1) / pagesize + 1) * pagesize;
+}
+
+// Return (and set null) g_cached_symbolized_state if it is not null.
+// Otherwise return a new symbolizer.
+static Symbolizer *AllocateSymbolizer() {
+  InitSigSafeArena();
+  Symbolizer *symbolizer =
+      g_cached_symbolizer.exchange(nullptr, std::memory_order_acquire);
+  if (symbolizer != nullptr) {
+    return symbolizer;
+  }
+  return new (base_internal::LowLevelAlloc::AllocWithArena(
+      SymbolizerSize(), SigSafeArena())) Symbolizer();
+}
+
+// Set g_cached_symbolize_state to s if it is null, otherwise
+// delete s.
+static void FreeSymbolizer(Symbolizer *s) {
+  Symbolizer *old_cached_symbolizer = nullptr;
+  if (!g_cached_symbolizer.compare_exchange_strong(old_cached_symbolizer, s,
+                                                   std::memory_order_release,
+                                                   std::memory_order_relaxed)) {
+    s->~Symbolizer();
+    base_internal::LowLevelAlloc::Free(s);
+  }
+}
+
+Symbolizer::Symbolizer() : ok_(true), addr_map_read_(false) {
+  for (SymbolCacheLine &symbol_cache_line : symbol_cache_) {
+    for (size_t j = 0; j < ABSL_ARRAYSIZE(symbol_cache_line.name); ++j) {
+      symbol_cache_line.pc[j] = nullptr;
+      symbol_cache_line.name[j] = nullptr;
+      symbol_cache_line.age[j] = 0;
+    }
+  }
+}
+
+Symbolizer::~Symbolizer() {
+  for (SymbolCacheLine &symbol_cache_line : symbol_cache_) {
+    for (char *s : symbol_cache_line.name) {
+      base_internal::LowLevelAlloc::Free(s);
+    }
+  }
+  ClearAddrMap();
+}
+
+// We don't use assert() since it's not guaranteed to be
+// async-signal-safe.  Instead we define a minimal assertion
+// macro. So far, we don't need pretty printing for __FILE__, etc.
+#define SAFE_ASSERT(expr) ((expr) ? static_cast<void>(0) : abort())
+
+// Read up to "count" bytes from file descriptor "fd" into the buffer
+// starting at "buf" while handling short reads and EINTR.  On
+// success, return the number of bytes read.  Otherwise, return -1.
+static ssize_t ReadPersistent(int fd, void *buf, size_t count) {
+  SAFE_ASSERT(fd >= 0);
+  SAFE_ASSERT(count <= SSIZE_MAX);
+  char *buf0 = reinterpret_cast<char *>(buf);
+  size_t num_bytes = 0;
+  while (num_bytes < count) {
+    ssize_t len;
+    NO_INTR(len = read(fd, buf0 + num_bytes, count - num_bytes));
+    if (len < 0) {  // There was an error other than EINTR.
+      ABSL_RAW_LOG(WARNING, "read failed: errno=%d", errno);
+      return -1;
+    }
+    if (len == 0) {  // Reached EOF.
+      break;
+    }
+    num_bytes += len;
+  }
+  SAFE_ASSERT(num_bytes <= count);
+  return static_cast<ssize_t>(num_bytes);
+}
+
+// Read up to "count" bytes from "offset" in the file pointed by file
+// descriptor "fd" into the buffer starting at "buf".  On success,
+// return the number of bytes read.  Otherwise, return -1.
+static ssize_t ReadFromOffset(const int fd, void *buf, const size_t count,
+                              const off_t offset) {
+  off_t off = lseek(fd, offset, SEEK_SET);
+  if (off == (off_t)-1) {
+    ABSL_RAW_LOG(WARNING, "lseek(%d, %ju, SEEK_SET) failed: errno=%d", fd,
+                 static_cast<uintmax_t>(offset), errno);
+    return -1;
+  }
+  return ReadPersistent(fd, buf, count);
+}
+
+// Try reading exactly "count" bytes from "offset" bytes in a file
+// pointed by "fd" into the buffer starting at "buf" while handling
+// short reads and EINTR.  On success, return true. Otherwise, return
+// false.
+static bool ReadFromOffsetExact(const int fd, void *buf, const size_t count,
+                                const off_t offset) {
+  ssize_t len = ReadFromOffset(fd, buf, count, offset);
+  return len >= 0 && static_cast<size_t>(len) == count;
+}
+
+// Returns elf_header.e_type if the file pointed by fd is an ELF binary.
+static int FileGetElfType(const int fd) {
+  ElfW(Ehdr) elf_header;
+  if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
+    return -1;
+  }
+  if (memcmp(elf_header.e_ident, ELFMAG, SELFMAG) != 0) {
+    return -1;
+  }
+  return elf_header.e_type;
+}
+
+// Read the section headers in the given ELF binary, and if a section
+// of the specified type is found, set the output to this section header
+// and return true.  Otherwise, return false.
+// To keep stack consumption low, we would like this function to not get
+// inlined.
+static ABSL_ATTRIBUTE_NOINLINE bool GetSectionHeaderByType(
+    const int fd, ElfW(Half) sh_num, const off_t sh_offset, ElfW(Word) type,
+    ElfW(Shdr) * out, char *tmp_buf, int tmp_buf_size) {
+  ElfW(Shdr) *buf = reinterpret_cast<ElfW(Shdr) *>(tmp_buf);
+  const int buf_entries = tmp_buf_size / sizeof(buf[0]);
+  const int buf_bytes = buf_entries * sizeof(buf[0]);
+
+  for (int i = 0; i < sh_num;) {
+    const ssize_t num_bytes_left = (sh_num - i) * sizeof(buf[0]);
+    const ssize_t num_bytes_to_read =
+        (buf_bytes > num_bytes_left) ? num_bytes_left : buf_bytes;
+    const off_t offset = sh_offset + i * sizeof(buf[0]);
+    const ssize_t len = ReadFromOffset(fd, buf, num_bytes_to_read, offset);
+    if (len % sizeof(buf[0]) != 0) {
+      ABSL_RAW_LOG(
+          WARNING,
+          "Reading %zd bytes from offset %ju returned %zd which is not a "
+          "multiple of %zu.",
+          num_bytes_to_read, static_cast<uintmax_t>(offset), len,
+          sizeof(buf[0]));
+      return false;
+    }
+    const ssize_t num_headers_in_buf = len / sizeof(buf[0]);
+    SAFE_ASSERT(num_headers_in_buf <= buf_entries);
+    for (int j = 0; j < num_headers_in_buf; ++j) {
+      if (buf[j].sh_type == type) {
+        *out = buf[j];
+        return true;
+      }
+    }
+    i += num_headers_in_buf;
+  }
+  return false;
+}
+
+// There is no particular reason to limit section name to 63 characters,
+// but there has (as yet) been no need for anything longer either.
+const int kMaxSectionNameLen = 64;
+
+bool ForEachSection(int fd,
+                    const std::function<bool(const std::string &name,
+                                             const ElfW(Shdr) &)> &callback) {
+  ElfW(Ehdr) elf_header;
+  if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
+    return false;
+  }
+
+  ElfW(Shdr) shstrtab;
+  off_t shstrtab_offset =
+      (elf_header.e_shoff + elf_header.e_shentsize * elf_header.e_shstrndx);
+  if (!ReadFromOffsetExact(fd, &shstrtab, sizeof(shstrtab), shstrtab_offset)) {
+    return false;
+  }
+
+  for (int i = 0; i < elf_header.e_shnum; ++i) {
+    ElfW(Shdr) out;
+    off_t section_header_offset =
+        (elf_header.e_shoff + elf_header.e_shentsize * i);
+    if (!ReadFromOffsetExact(fd, &out, sizeof(out), section_header_offset)) {
+      return false;
+    }
+    off_t name_offset = shstrtab.sh_offset + out.sh_name;
+    char header_name[kMaxSectionNameLen + 1];
+    ssize_t n_read =
+        ReadFromOffset(fd, &header_name, kMaxSectionNameLen, name_offset);
+    if (n_read == -1) {
+      return false;
+    } else if (n_read > kMaxSectionNameLen) {
+      // Long read?
+      return false;
+    }
+    header_name[n_read] = '\0';
+
+    std::string name(header_name);
+    if (!callback(name, out)) {
+      break;
+    }
+  }
+  return true;
+}
+
+// name_len should include terminating '\0'.
+bool GetSectionHeaderByName(int fd, const char *name, size_t name_len,
+                            ElfW(Shdr) * out) {
+  char header_name[kMaxSectionNameLen];
+  if (sizeof(header_name) < name_len) {
+    ABSL_RAW_LOG(WARNING,
+                 "Section name '%s' is too long (%zu); "
+                 "section will not be found (even if present).",
+                 name, name_len);
+    // No point in even trying.
+    return false;
+  }
+
+  ElfW(Ehdr) elf_header;
+  if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
+    return false;
+  }
+
+  ElfW(Shdr) shstrtab;
+  off_t shstrtab_offset =
+      (elf_header.e_shoff + elf_header.e_shentsize * elf_header.e_shstrndx);
+  if (!ReadFromOffsetExact(fd, &shstrtab, sizeof(shstrtab), shstrtab_offset)) {
+    return false;
+  }
+
+  for (int i = 0; i < elf_header.e_shnum; ++i) {
+    off_t section_header_offset =
+        (elf_header.e_shoff + elf_header.e_shentsize * i);
+    if (!ReadFromOffsetExact(fd, out, sizeof(*out), section_header_offset)) {
+      return false;
+    }
+    off_t name_offset = shstrtab.sh_offset + out->sh_name;
+    ssize_t n_read = ReadFromOffset(fd, &header_name, name_len, name_offset);
+    if (n_read < 0) {
+      return false;
+    } else if (static_cast<size_t>(n_read) != name_len) {
+      // Short read -- name could be at end of file.
+      continue;
+    }
+    if (memcmp(header_name, name, name_len) == 0) {
+      return true;
+    }
+  }
+  return false;
+}
+
+// Compare symbols at in the same address.
+// Return true if we should pick symbol1.
+static bool ShouldPickFirstSymbol(const ElfW(Sym) & symbol1,
+                                  const ElfW(Sym) & symbol2) {
+  // If one of the symbols is weak and the other is not, pick the one
+  // this is not a weak symbol.
+  char bind1 = ELF_ST_BIND(symbol1.st_info);
+  char bind2 = ELF_ST_BIND(symbol1.st_info);
+  if (bind1 == STB_WEAK && bind2 != STB_WEAK) return false;
+  if (bind2 == STB_WEAK && bind1 != STB_WEAK) return true;
+
+  // If one of the symbols has zero size and the other is not, pick the
+  // one that has non-zero size.
+  if (symbol1.st_size != 0 && symbol2.st_size == 0) {
+    return true;
+  }
+  if (symbol1.st_size == 0 && symbol2.st_size != 0) {
+    return false;
+  }
+
+  // If one of the symbols has no type and the other is not, pick the
+  // one that has a type.
+  char type1 = ELF_ST_TYPE(symbol1.st_info);
+  char type2 = ELF_ST_TYPE(symbol1.st_info);
+  if (type1 != STT_NOTYPE && type2 == STT_NOTYPE) {
+    return true;
+  }
+  if (type1 == STT_NOTYPE && type2 != STT_NOTYPE) {
+    return false;
+  }
+
+  // Pick the first one, if we still cannot decide.
+  return true;
+}
+
+// Return true if an address is inside a section.
+static bool InSection(const void *address, const ElfW(Shdr) * section) {
+  const char *start = reinterpret_cast<const char *>(section->sh_addr);
+  size_t size = static_cast<size_t>(section->sh_size);
+  return start <= address && address < (start + size);
+}
+
+static const char *ComputeOffset(const char *base, ptrdiff_t offset) {
+  // Note: cast to uintptr_t to avoid undefined behavior when base evaluates to
+  // zero and offset is non-zero.
+  return reinterpret_cast<const char *>(
+      reinterpret_cast<uintptr_t>(base) + offset);
+}
+
+// Read a symbol table and look for the symbol containing the
+// pc. Iterate over symbols in a symbol table and look for the symbol
+// containing "pc".  If the symbol is found, and its name fits in
+// out_size, the name is written into out and SYMBOL_FOUND is returned.
+// If the name does not fit, truncated name is written into out,
+// and SYMBOL_TRUNCATED is returned. Out is NUL-terminated.
+// If the symbol is not found, SYMBOL_NOT_FOUND is returned;
+// To keep stack consumption low, we would like this function to not get
+// inlined.
+static ABSL_ATTRIBUTE_NOINLINE FindSymbolResult FindSymbol(
+    const void *const pc, const int fd, char *out, int out_size,
+    ptrdiff_t relocation, const ElfW(Shdr) * strtab, const ElfW(Shdr) * symtab,
+    const ElfW(Shdr) * opd, char *tmp_buf, int tmp_buf_size) {
+  if (symtab == nullptr) {
+    return SYMBOL_NOT_FOUND;
+  }
+
+  // Read multiple symbols at once to save read() calls.
+  ElfW(Sym) *buf = reinterpret_cast<ElfW(Sym) *>(tmp_buf);
+  const int buf_entries = tmp_buf_size / sizeof(buf[0]);
+
+  const int num_symbols = symtab->sh_size / symtab->sh_entsize;
+
+  // On platforms using an .opd section (PowerPC & IA64), a function symbol
+  // has the address of a function descriptor, which contains the real
+  // starting address.  However, we do not always want to use the real
+  // starting address because we sometimes want to symbolize a function
+  // pointer into the .opd section, e.g. FindSymbol(&foo,...).
+  const bool pc_in_opd =
+      kPlatformUsesOPDSections && opd != nullptr && InSection(pc, opd);
+  const bool deref_function_descriptor_pointer =
+      kPlatformUsesOPDSections && opd != nullptr && !pc_in_opd;
+
+  ElfW(Sym) best_match;
+  SafeMemZero(&best_match, sizeof(best_match));
+  bool found_match = false;
+  for (int i = 0; i < num_symbols;) {
+    off_t offset = symtab->sh_offset + i * symtab->sh_entsize;
+    const int num_remaining_symbols = num_symbols - i;
+    const int entries_in_chunk = std::min(num_remaining_symbols, buf_entries);
+    const int bytes_in_chunk = entries_in_chunk * sizeof(buf[0]);
+    const ssize_t len = ReadFromOffset(fd, buf, bytes_in_chunk, offset);
+    SAFE_ASSERT(len % sizeof(buf[0]) == 0);
+    const ssize_t num_symbols_in_buf = len / sizeof(buf[0]);
+    SAFE_ASSERT(num_symbols_in_buf <= entries_in_chunk);
+    for (int j = 0; j < num_symbols_in_buf; ++j) {
+      const ElfW(Sym) &symbol = buf[j];
+
+      // For a DSO, a symbol address is relocated by the loading address.
+      // We keep the original address for opd redirection below.
+      const char *const original_start_address =
+          reinterpret_cast<const char *>(symbol.st_value);
+      const char *start_address =
+          ComputeOffset(original_start_address, relocation);
+
+      if (deref_function_descriptor_pointer &&
+          InSection(original_start_address, opd)) {
+        // The opd section is mapped into memory.  Just dereference
+        // start_address to get the first double word, which points to the
+        // function entry.
+        start_address = *reinterpret_cast<const char *const *>(start_address);
+      }
+
+      // If pc is inside the .opd section, it points to a function descriptor.
+      const size_t size = pc_in_opd ? kFunctionDescriptorSize : symbol.st_size;
+      const void *const end_address = ComputeOffset(start_address, size);
+      if (symbol.st_value != 0 &&  // Skip null value symbols.
+          symbol.st_shndx != 0 &&  // Skip undefined symbols.
+#ifdef STT_TLS
+          ELF_ST_TYPE(symbol.st_info) != STT_TLS &&  // Skip thread-local data.
+#endif                                               // STT_TLS
+          ((start_address <= pc && pc < end_address) ||
+           (start_address == pc && pc == end_address))) {
+        if (!found_match || ShouldPickFirstSymbol(symbol, best_match)) {
+          found_match = true;
+          best_match = symbol;
+        }
+      }
+    }
+    i += num_symbols_in_buf;
+  }
+
+  if (found_match) {
+    const size_t off = strtab->sh_offset + best_match.st_name;
+    const ssize_t n_read = ReadFromOffset(fd, out, out_size, off);
+    if (n_read <= 0) {
+      // This should never happen.
+      ABSL_RAW_LOG(WARNING,
+                   "Unable to read from fd %d at offset %zu: n_read = %zd", fd,
+                   off, n_read);
+      return SYMBOL_NOT_FOUND;
+    }
+    ABSL_RAW_CHECK(n_read <= out_size, "ReadFromOffset read too much data.");
+
+    // strtab->sh_offset points into .strtab-like section that contains
+    // NUL-terminated strings: '\0foo\0barbaz\0...".
+    //
+    // sh_offset+st_name points to the start of symbol name, but we don't know
+    // how long the symbol is, so we try to read as much as we have space for,
+    // and usually over-read (i.e. there is a NUL somewhere before n_read).
+    if (memchr(out, '\0', n_read) == nullptr) {
+      // Either out_size was too small (n_read == out_size and no NUL), or
+      // we tried to read past the EOF (n_read < out_size) and .strtab is
+      // corrupt (missing terminating NUL; should never happen for valid ELF).
+      out[n_read - 1] = '\0';
+      return SYMBOL_TRUNCATED;
+    }
+    return SYMBOL_FOUND;
+  }
+
+  return SYMBOL_NOT_FOUND;
+}
+
+// Get the symbol name of "pc" from the file pointed by "fd".  Process
+// both regular and dynamic symbol tables if necessary.
+// See FindSymbol() comment for description of return value.
+FindSymbolResult Symbolizer::GetSymbolFromObjectFile(
+    const ObjFile &obj, const void *const pc, const ptrdiff_t relocation,
+    char *out, int out_size, char *tmp_buf, int tmp_buf_size) {
+  ElfW(Shdr) symtab;
+  ElfW(Shdr) strtab;
+  ElfW(Shdr) opd;
+  ElfW(Shdr) *opd_ptr = nullptr;
+
+  // On platforms using an .opd sections for function descriptor, read
+  // the section header.  The .opd section is in data segment and should be
+  // loaded but we check that it is mapped just to be extra careful.
+  if (kPlatformUsesOPDSections) {
+    if (GetSectionHeaderByName(obj.fd, kOpdSectionName,
+                               sizeof(kOpdSectionName) - 1, &opd) &&
+        FindObjFile(reinterpret_cast<const char *>(opd.sh_addr) + relocation,
+                    opd.sh_size) != nullptr) {
+      opd_ptr = &opd;
+    } else {
+      return SYMBOL_NOT_FOUND;
+    }
+  }
+
+  // Consult a regular symbol table, then fall back to the dynamic symbol table.
+  for (const auto symbol_table_type : {SHT_SYMTAB, SHT_DYNSYM}) {
+    if (!GetSectionHeaderByType(obj.fd, obj.elf_header.e_shnum,
+                                obj.elf_header.e_shoff, symbol_table_type,
+                                &symtab, tmp_buf, tmp_buf_size)) {
+      continue;
+    }
+    if (!ReadFromOffsetExact(
+            obj.fd, &strtab, sizeof(strtab),
+            obj.elf_header.e_shoff + symtab.sh_link * sizeof(symtab))) {
+      continue;
+    }
+    const FindSymbolResult rc =
+        FindSymbol(pc, obj.fd, out, out_size, relocation, &strtab, &symtab,
+                   opd_ptr, tmp_buf, tmp_buf_size);
+    if (rc != SYMBOL_NOT_FOUND) {
+      return rc;
+    }
+  }
+
+  return SYMBOL_NOT_FOUND;
+}
+
+namespace {
+// Thin wrapper around a file descriptor so that the file descriptor
+// gets closed for sure.
+class FileDescriptor {
+ public:
+  explicit FileDescriptor(int fd) : fd_(fd) {}
+  FileDescriptor(const FileDescriptor &) = delete;
+  FileDescriptor &operator=(const FileDescriptor &) = delete;
+
+  ~FileDescriptor() {
+    if (fd_ >= 0) {
+      NO_INTR(close(fd_));
+    }
+  }
+
+  int get() const { return fd_; }
+
+ private:
+  const int fd_;
+};
+
+// Helper class for reading lines from file.
+//
+// Note: we don't use ProcMapsIterator since the object is big (it has
+// a 5k array member) and uses async-unsafe functions such as sscanf()
+// and snprintf().
+class LineReader {
+ public:
+  explicit LineReader(int fd, char *buf, int buf_len)
+      : fd_(fd),
+        buf_len_(buf_len),
+        buf_(buf),
+        bol_(buf),
+        eol_(buf),
+        eod_(buf) {}
+
+  LineReader(const LineReader &) = delete;
+  LineReader &operator=(const LineReader &) = delete;
+
+  // Read '\n'-terminated line from file.  On success, modify "bol"
+  // and "eol", then return true.  Otherwise, return false.
+  //
+  // Note: if the last line doesn't end with '\n', the line will be
+  // dropped.  It's an intentional behavior to make the code simple.
+  bool ReadLine(const char **bol, const char **eol) {
+    if (BufferIsEmpty()) {  // First time.
+      const ssize_t num_bytes = ReadPersistent(fd_, buf_, buf_len_);
+      if (num_bytes <= 0) {  // EOF or error.
+        return false;
+      }
+      eod_ = buf_ + num_bytes;
+      bol_ = buf_;
+    } else {
+      bol_ = eol_ + 1;            // Advance to the next line in the buffer.
+      SAFE_ASSERT(bol_ <= eod_);  // "bol_" can point to "eod_".
+      if (!HasCompleteLine()) {
+        const int incomplete_line_length = eod_ - bol_;
+        // Move the trailing incomplete line to the beginning.
+        memmove(buf_, bol_, incomplete_line_length);
+        // Read text from file and append it.
+        char *const append_pos = buf_ + incomplete_line_length;
+        const int capacity_left = buf_len_ - incomplete_line_length;
+        const ssize_t num_bytes =
+            ReadPersistent(fd_, append_pos, capacity_left);
+        if (num_bytes <= 0) {  // EOF or error.
+          return false;
+        }
+        eod_ = append_pos + num_bytes;
+        bol_ = buf_;
+      }
+    }
+    eol_ = FindLineFeed();
+    if (eol_ == nullptr) {  // '\n' not found.  Malformed line.
+      return false;
+    }
+    *eol_ = '\0';  // Replace '\n' with '\0'.
+
+    *bol = bol_;
+    *eol = eol_;
+    return true;
+  }
+
+ private:
+  char *FindLineFeed() const {
+    return reinterpret_cast<char *>(memchr(bol_, '\n', eod_ - bol_));
+  }
+
+  bool BufferIsEmpty() const { return buf_ == eod_; }
+
+  bool HasCompleteLine() const {
+    return !BufferIsEmpty() && FindLineFeed() != nullptr;
+  }
+
+  const int fd_;
+  const int buf_len_;
+  char *const buf_;
+  char *bol_;
+  char *eol_;
+  const char *eod_;  // End of data in "buf_".
+};
+}  // namespace
+
+// Place the hex number read from "start" into "*hex".  The pointer to
+// the first non-hex character or "end" is returned.
+static const char *GetHex(const char *start, const char *end,
+                          uint64_t *const value) {
+  uint64_t hex = 0;
+  const char *p;
+  for (p = start; p < end; ++p) {
+    int ch = *p;
+    if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'F') ||
+        (ch >= 'a' && ch <= 'f')) {
+      hex = (hex << 4) | (ch < 'A' ? ch - '0' : (ch & 0xF) + 9);
+    } else {  // Encountered the first non-hex character.
+      break;
+    }
+  }
+  SAFE_ASSERT(p <= end);
+  *value = hex;
+  return p;
+}
+
+static const char *GetHex(const char *start, const char *end,
+                          const void **const addr) {
+  uint64_t hex = 0;
+  const char *p = GetHex(start, end, &hex);
+  *addr = reinterpret_cast<void *>(hex);
+  return p;
+}
+
+// Normally we are only interested in "r?x" maps.
+// On the PowerPC, function pointers point to descriptors in the .opd
+// section.  The descriptors themselves are not executable code, so
+// we need to relax the check below to "r??".
+static bool ShouldUseMapping(const char *const flags) {
+  return flags[0] == 'r' && (kPlatformUsesOPDSections || flags[2] == 'x');
+}
+
+// Read /proc/self/maps and run "callback" for each mmapped file found.  If
+// "callback" returns false, stop scanning and return true. Else continue
+// scanning /proc/self/maps. Return true if no parse error is found.
+static ABSL_ATTRIBUTE_NOINLINE bool ReadAddrMap(
+    bool (*callback)(const char *filename, const void *const start_addr,
+                     const void *const end_addr, uint64_t offset, void *arg),
+    void *arg, void *tmp_buf, int tmp_buf_size) {
+  // Use /proc/self/task/<pid>/maps instead of /proc/self/maps. The latter
+  // requires kernel to stop all threads, and is significantly slower when there
+  // are 1000s of threads.
+  char maps_path[80];
+  snprintf(maps_path, sizeof(maps_path), "/proc/self/task/%d/maps", getpid());
+
+  int maps_fd;
+  NO_INTR(maps_fd = open(maps_path, O_RDONLY));
+  FileDescriptor wrapped_maps_fd(maps_fd);
+  if (wrapped_maps_fd.get() < 0) {
+    ABSL_RAW_LOG(WARNING, "%s: errno=%d", maps_path, errno);
+    return false;
+  }
+
+  // Iterate over maps and look for the map containing the pc.  Then
+  // look into the symbol tables inside.
+  LineReader reader(wrapped_maps_fd.get(), static_cast<char *>(tmp_buf),
+                    tmp_buf_size);
+  while (true) {
+    const char *cursor;
+    const char *eol;
+    if (!reader.ReadLine(&cursor, &eol)) {  // EOF or malformed line.
+      break;
+    }
+
+    const char *line = cursor;
+    const void *start_address;
+    // Start parsing line in /proc/self/maps.  Here is an example:
+    //
+    // 08048000-0804c000 r-xp 00000000 08:01 2142121    /bin/cat
+    //
+    // We want start address (08048000), end address (0804c000), flags
+    // (r-xp) and file name (/bin/cat).
+
+    // Read start address.
+    cursor = GetHex(cursor, eol, &start_address);
+    if (cursor == eol || *cursor != '-') {
+      ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps line: %s", line);
+      return false;
+    }
+    ++cursor;  // Skip '-'.
+
+    // Read end address.
+    const void *end_address;
+    cursor = GetHex(cursor, eol, &end_address);
+    if (cursor == eol || *cursor != ' ') {
+      ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps line: %s", line);
+      return false;
+    }
+    ++cursor;  // Skip ' '.
+
+    // Read flags.  Skip flags until we encounter a space or eol.
+    const char *const flags_start = cursor;
+    while (cursor < eol && *cursor != ' ') {
+      ++cursor;
+    }
+    // We expect at least four letters for flags (ex. "r-xp").
+    if (cursor == eol || cursor < flags_start + 4) {
+      ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps: %s", line);
+      return false;
+    }
+
+    // Check flags.
+    if (!ShouldUseMapping(flags_start)) {
+      continue;  // We skip this map.
+    }
+    ++cursor;  // Skip ' '.
+
+    // Read file offset.
+    uint64_t offset;
+    cursor = GetHex(cursor, eol, &offset);
+    ++cursor;  // Skip ' '.
+
+    // Skip to file name.  "cursor" now points to dev.  We need to skip at least
+    // two spaces for dev and inode.
+    int num_spaces = 0;
+    while (cursor < eol) {
+      if (*cursor == ' ') {
+        ++num_spaces;
+      } else if (num_spaces >= 2) {
+        // The first non-space character after  skipping two spaces
+        // is the beginning of the file name.
+        break;
+      }
+      ++cursor;
+    }
+
+    // Check whether this entry corresponds to our hint table for the true
+    // filename.
+    bool hinted =
+        GetFileMappingHint(&start_address, &end_address, &offset, &cursor);
+    if (!hinted && (cursor == eol || cursor[0] == '[')) {
+      // not an object file, typically [vdso] or [vsyscall]
+      continue;
+    }
+    if (!callback(cursor, start_address, end_address, offset, arg)) break;
+  }
+  return true;
+}
+
+// Find the objfile mapped in address region containing [addr, addr + len).
+ObjFile *Symbolizer::FindObjFile(const void *const addr, size_t len) {
+  for (int i = 0; i < 2; ++i) {
+    if (!ok_) return nullptr;
+
+    // Read /proc/self/maps if necessary
+    if (!addr_map_read_) {
+      addr_map_read_ = true;
+      if (!ReadAddrMap(RegisterObjFile, this, tmp_buf_, TMP_BUF_SIZE)) {
+        ok_ = false;
+        return nullptr;
+      }
+    }
+
+    int lo = 0;
+    int hi = addr_map_.Size();
+    while (lo < hi) {
+      int mid = (lo + hi) / 2;
+      if (addr < addr_map_.At(mid)->end_addr) {
+        hi = mid;
+      } else {
+        lo = mid + 1;
+      }
+    }
+    if (lo != addr_map_.Size()) {
+      ObjFile *obj = addr_map_.At(lo);
+      SAFE_ASSERT(obj->end_addr > addr);
+      if (addr >= obj->start_addr &&
+          reinterpret_cast<const char *>(addr) + len <= obj->end_addr)
+        return obj;
+    }
+
+    // The address mapping may have changed since it was last read.  Retry.
+    ClearAddrMap();
+  }
+  return nullptr;
+}
+
+void Symbolizer::ClearAddrMap() {
+  for (int i = 0; i != addr_map_.Size(); i++) {
+    ObjFile *o = addr_map_.At(i);
+    base_internal::LowLevelAlloc::Free(o->filename);
+    if (o->fd >= 0) {
+      NO_INTR(close(o->fd));
+    }
+  }
+  addr_map_.Clear();
+  addr_map_read_ = false;
+}
+
+// Callback for ReadAddrMap to register objfiles in an in-memory table.
+bool Symbolizer::RegisterObjFile(const char *filename,
+                                 const void *const start_addr,
+                                 const void *const end_addr, uint64_t offset,
+                                 void *arg) {
+  Symbolizer *impl = static_cast<Symbolizer *>(arg);
+
+  // Files are supposed to be added in the increasing address order.  Make
+  // sure that's the case.
+  int addr_map_size = impl->addr_map_.Size();
+  if (addr_map_size != 0) {
+    ObjFile *old = impl->addr_map_.At(addr_map_size - 1);
+    if (old->end_addr > end_addr) {
+      ABSL_RAW_LOG(ERROR,
+                   "Unsorted addr map entry: 0x%" PRIxPTR ": %s <-> 0x%" PRIxPTR
+                   ": %s",
+                   reinterpret_cast<uintptr_t>(end_addr), filename,
+                   reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
+      return true;
+    } else if (old->end_addr == end_addr) {
+      // The same entry appears twice. This sometimes happens for [vdso].
+      if (old->start_addr != start_addr ||
+          strcmp(old->filename, filename) != 0) {
+        ABSL_RAW_LOG(ERROR,
+                     "Duplicate addr 0x%" PRIxPTR ": %s <-> 0x%" PRIxPTR ": %s",
+                     reinterpret_cast<uintptr_t>(end_addr), filename,
+                     reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
+      }
+      return true;
+    }
+  }
+  ObjFile *obj = impl->addr_map_.Add();
+  obj->filename = impl->CopyString(filename);
+  obj->start_addr = start_addr;
+  obj->end_addr = end_addr;
+  obj->offset = offset;
+  obj->elf_type = -1;  // filled on demand
+  obj->fd = -1;        // opened on demand
+  return true;
+}
+
+// This function wraps the Demangle function to provide an interface
+// where the input symbol is demangled in-place.
+// To keep stack consumption low, we would like this function to not
+// get inlined.
+static ABSL_ATTRIBUTE_NOINLINE void DemangleInplace(char *out, int out_size,
+                                                    char *tmp_buf,
+                                                    int tmp_buf_size) {
+  if (Demangle(out, tmp_buf, tmp_buf_size)) {
+    // Demangling succeeded. Copy to out if the space allows.
+    int len = strlen(tmp_buf);
+    if (len + 1 <= out_size) {  // +1 for '\0'.
+      SAFE_ASSERT(len < tmp_buf_size);
+      memmove(out, tmp_buf, len + 1);
+    }
+  }
+}
+
+SymbolCacheLine *Symbolizer::GetCacheLine(const void *const pc) {
+  uintptr_t pc0 = reinterpret_cast<uintptr_t>(pc);
+  pc0 >>= 3;  // drop the low 3 bits
+
+  // Shuffle bits.
+  pc0 ^= (pc0 >> 6) ^ (pc0 >> 12) ^ (pc0 >> 18);
+  return &symbol_cache_[pc0 % SYMBOL_CACHE_LINES];
+}
+
+void Symbolizer::AgeSymbols(SymbolCacheLine *line) {
+  for (uint32_t &age : line->age) {
+    ++age;
+  }
+}
+
+const char *Symbolizer::FindSymbolInCache(const void *const pc) {
+  if (pc == nullptr) return nullptr;
+
+  SymbolCacheLine *line = GetCacheLine(pc);
+  for (size_t i = 0; i < ABSL_ARRAYSIZE(line->pc); ++i) {
+    if (line->pc[i] == pc) {
+      AgeSymbols(line);
+      line->age[i] = 0;
+      return line->name[i];
+    }
+  }
+  return nullptr;
+}
+
+const char *Symbolizer::InsertSymbolInCache(const void *const pc,
+                                            const char *name) {
+  SAFE_ASSERT(pc != nullptr);
+
+  SymbolCacheLine *line = GetCacheLine(pc);
+  uint32_t max_age = 0;
+  int oldest_index = -1;
+  for (size_t i = 0; i < ABSL_ARRAYSIZE(line->pc); ++i) {
+    if (line->pc[i] == nullptr) {
+      AgeSymbols(line);
+      line->pc[i] = pc;
+      line->name[i] = CopyString(name);
+      line->age[i] = 0;
+      return line->name[i];
+    }
+    if (line->age[i] >= max_age) {
+      max_age = line->age[i];
+      oldest_index = i;
+    }
+  }
+
+  AgeSymbols(line);
+  ABSL_RAW_CHECK(oldest_index >= 0, "Corrupt cache");
+  base_internal::LowLevelAlloc::Free(line->name[oldest_index]);
+  line->pc[oldest_index] = pc;
+  line->name[oldest_index] = CopyString(name);
+  line->age[oldest_index] = 0;
+  return line->name[oldest_index];
+}
+
+static void MaybeOpenFdFromSelfExe(ObjFile *obj) {
+  if (memcmp(obj->start_addr, ELFMAG, SELFMAG) != 0) {
+    return;
+  }
+  int fd = open("/proc/self/exe", O_RDONLY);
+  if (fd == -1) {
+    return;
+  }
+  // Verify that contents of /proc/self/exe matches in-memory image of
+  // the binary. This can fail if the "deleted" binary is in fact not
+  // the main executable, or for binaries that have the first PT_LOAD
+  // segment smaller than 4K. We do it in four steps so that the
+  // buffer is smaller and we don't consume too much stack space.
+  const char *mem = reinterpret_cast<const char *>(obj->start_addr);
+  for (int i = 0; i < 4; ++i) {
+    char buf[1024];
+    ssize_t n = read(fd, buf, sizeof(buf));
+    if (n != sizeof(buf) || memcmp(buf, mem, sizeof(buf)) != 0) {
+      close(fd);
+      return;
+    }
+    mem += sizeof(buf);
+  }
+  obj->fd = fd;
+}
+
+static bool MaybeInitializeObjFile(ObjFile *obj) {
+  if (obj->fd < 0) {
+    obj->fd = open(obj->filename, O_RDONLY);
+
+    if (obj->fd < 0) {
+      // Getting /proc/self/exe here means that we were hinted.
+      if (strcmp(obj->filename, "/proc/self/exe") == 0) {
+        // /proc/self/exe may be inaccessible (due to setuid, etc.), so try
+        // accessing the binary via argv0.
+        if (argv0_value != nullptr) {
+          obj->fd = open(argv0_value, O_RDONLY);
+        }
+      } else {
+        MaybeOpenFdFromSelfExe(obj);
+      }
+    }
+
+    if (obj->fd < 0) {
+      ABSL_RAW_LOG(WARNING, "%s: open failed: errno=%d", obj->filename, errno);
+      return false;
+    }
+    obj->elf_type = FileGetElfType(obj->fd);
+    if (obj->elf_type < 0) {
+      ABSL_RAW_LOG(WARNING, "%s: wrong elf type: %d", obj->filename,
+                   obj->elf_type);
+      return false;
+    }
+
+    if (!ReadFromOffsetExact(obj->fd, &obj->elf_header, sizeof(obj->elf_header),
+                             0)) {
+      ABSL_RAW_LOG(WARNING, "%s: failed to read elf header", obj->filename);
+      return false;
+    }
+  }
+  return true;
+}
+
+// The implementation of our symbolization routine.  If it
+// successfully finds the symbol containing "pc" and obtains the
+// symbol name, returns pointer to that symbol. Otherwise, returns nullptr.
+// If any symbol decorators have been installed via InstallSymbolDecorator(),
+// they are called here as well.
+// To keep stack consumption low, we would like this function to not
+// get inlined.
+const char *Symbolizer::GetSymbol(const void *const pc) {
+  const char *entry = FindSymbolInCache(pc);
+  if (entry != nullptr) {
+    return entry;
+  }
+  symbol_buf_[0] = '\0';
+
+  ObjFile *const obj = FindObjFile(pc, 1);
+  ptrdiff_t relocation = 0;
+  int fd = -1;
+  if (obj != nullptr) {
+    if (MaybeInitializeObjFile(obj)) {
+      if (obj->elf_type == ET_DYN &&
+          reinterpret_cast<uint64_t>(obj->start_addr) >= obj->offset) {
+        // This object was relocated.
+        //
+        // For obj->offset > 0, adjust the relocation since a mapping at offset
+        // X in the file will have a start address of [true relocation]+X.
+        relocation = reinterpret_cast<ptrdiff_t>(obj->start_addr) - obj->offset;
+      }
+
+      fd = obj->fd;
+    }
+    if (GetSymbolFromObjectFile(*obj, pc, relocation, symbol_buf_,
+                                sizeof(symbol_buf_), tmp_buf_,
+                                sizeof(tmp_buf_)) == SYMBOL_FOUND) {
+      // Only try to demangle the symbol name if it fit into symbol_buf_.
+      DemangleInplace(symbol_buf_, sizeof(symbol_buf_), tmp_buf_,
+                      sizeof(tmp_buf_));
+    }
+  } else {
+#if ABSL_HAVE_VDSO_SUPPORT
+    VDSOSupport vdso;
+    if (vdso.IsPresent()) {
+      VDSOSupport::SymbolInfo symbol_info;
+      if (vdso.LookupSymbolByAddress(pc, &symbol_info)) {
+        // All VDSO symbols are known to be short.
+        size_t len = strlen(symbol_info.name);
+        ABSL_RAW_CHECK(len + 1 < sizeof(symbol_buf_),
+                       "VDSO symbol unexpectedly long");
+        memcpy(symbol_buf_, symbol_info.name, len + 1);
+      }
+    }
+#endif
+  }
+
+  if (g_decorators_mu.TryLock()) {
+    if (g_num_decorators > 0) {
+      SymbolDecoratorArgs decorator_args = {
+          pc,       relocation,       fd,     symbol_buf_, sizeof(symbol_buf_),
+          tmp_buf_, sizeof(tmp_buf_), nullptr};
+      for (int i = 0; i < g_num_decorators; ++i) {
+        decorator_args.arg = g_decorators[i].arg;
+        g_decorators[i].fn(&decorator_args);
+      }
+    }
+    g_decorators_mu.Unlock();
+  }
+  if (symbol_buf_[0] == '\0') {
+    return nullptr;
+  }
+  symbol_buf_[sizeof(symbol_buf_) - 1] = '\0';  // Paranoia.
+  return InsertSymbolInCache(pc, symbol_buf_);
+}
+
+bool RemoveAllSymbolDecorators(void) {
+  if (!g_decorators_mu.TryLock()) {
+    // Someone else is using decorators. Get out.
+    return false;
+  }
+  g_num_decorators = 0;
+  g_decorators_mu.Unlock();
+  return true;
+}
+
+bool RemoveSymbolDecorator(int ticket) {
+  if (!g_decorators_mu.TryLock()) {
+    // Someone else is using decorators. Get out.
+    return false;
+  }
+  for (int i = 0; i < g_num_decorators; ++i) {
+    if (g_decorators[i].ticket == ticket) {
+      while (i < g_num_decorators - 1) {
+        g_decorators[i] = g_decorators[i + 1];
+        ++i;
+      }
+      g_num_decorators = i;
+      break;
+    }
+  }
+  g_decorators_mu.Unlock();
+  return true;  // Decorator is known to be removed.
+}
+
+int InstallSymbolDecorator(SymbolDecorator decorator, void *arg) {
+  static int ticket = 0;
+
+  if (!g_decorators_mu.TryLock()) {
+    // Someone else is using decorators. Get out.
+    return false;
+  }
+  int ret = ticket;
+  if (g_num_decorators >= kMaxDecorators) {
+    ret = -1;
+  } else {
+    g_decorators[g_num_decorators] = {decorator, arg, ticket++};
+    ++g_num_decorators;
+  }
+  g_decorators_mu.Unlock();
+  return ret;
+}
+
+bool RegisterFileMappingHint(const void *start, const void *end, uint64_t offset,
+                             const char *filename) {
+  SAFE_ASSERT(start <= end);
+  SAFE_ASSERT(filename != nullptr);
+
+  InitSigSafeArena();
+
+  if (!g_file_mapping_mu.TryLock()) {
+    return false;
+  }
+
+  bool ret = true;
+  if (g_num_file_mapping_hints >= kMaxFileMappingHints) {
+    ret = false;
+  } else {
+    // TODO(ckennelly): Move this into a string copy routine.
+    int len = strlen(filename);
+    char *dst = static_cast<char *>(
+        base_internal::LowLevelAlloc::AllocWithArena(len + 1, SigSafeArena()));
+    ABSL_RAW_CHECK(dst != nullptr, "out of memory");
+    memcpy(dst, filename, len + 1);
+
+    auto &hint = g_file_mapping_hints[g_num_file_mapping_hints++];
+    hint.start = start;
+    hint.end = end;
+    hint.offset = offset;
+    hint.filename = dst;
+  }
+
+  g_file_mapping_mu.Unlock();
+  return ret;
+}
+
+bool GetFileMappingHint(const void **start, const void **end, uint64_t *offset,
+                        const char **filename) {
+  if (!g_file_mapping_mu.TryLock()) {
+    return false;
+  }
+  bool found = false;
+  for (int i = 0; i < g_num_file_mapping_hints; i++) {
+    if (g_file_mapping_hints[i].start <= *start &&
+        *end <= g_file_mapping_hints[i].end) {
+      // We assume that the start_address for the mapping is the base
+      // address of the ELF section, but when [start_address,end_address) is
+      // not strictly equal to [hint.start, hint.end), that assumption is
+      // invalid.
+      //
+      // This uses the hint's start address (even though hint.start is not
+      // necessarily equal to start_address) to ensure the correct
+      // relocation is computed later.
+      *start = g_file_mapping_hints[i].start;
+      *end = g_file_mapping_hints[i].end;
+      *offset = g_file_mapping_hints[i].offset;
+      *filename = g_file_mapping_hints[i].filename;
+      found = true;
+      break;
+    }
+  }
+  g_file_mapping_mu.Unlock();
+  return found;
+}
+
+}  // namespace debugging_internal
+
+bool Symbolize(const void *pc, char *out, int out_size) {
+  // Symbolization is very slow under tsan.
+  ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN();
+  SAFE_ASSERT(out_size >= 0);
+  debugging_internal::Symbolizer *s = debugging_internal::AllocateSymbolizer();
+  const char *name = s->GetSymbol(pc);
+  bool ok = false;
+  if (name != nullptr && out_size > 0) {
+    strncpy(out, name, out_size);
+    ok = true;
+    if (out[out_size - 1] != '\0') {
+      // strncpy() does not '\0' terminate when it truncates.  Do so, with
+      // trailing ellipsis.
+      static constexpr char kEllipsis[] = "...";
+      int ellipsis_size =
+          std::min(implicit_cast<int>(strlen(kEllipsis)), out_size - 1);
+      memcpy(out + out_size - ellipsis_size - 1, kEllipsis, ellipsis_size);
+      out[out_size - 1] = '\0';
+    }
+  }
+  debugging_internal::FreeSymbolizer(s);
+  ANNOTATE_IGNORE_READS_AND_WRITES_END();
+  return ok;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/symbolize_test.cc b/third_party/abseil_cpp/absl/debugging/symbolize_test.cc
new file mode 100644
index 000000000000..a1d03aab531b
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/symbolize_test.cc
@@ -0,0 +1,551 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/debugging/symbolize.h"
+
+#ifndef _WIN32
+#include <fcntl.h>
+#include <sys/mman.h>
+#endif
+
+#include <cstring>
+#include <iostream>
+#include <memory>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/attributes.h"
+#include "absl/base/casts.h"
+#include "absl/base/internal/per_thread_tls.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/optimization.h"
+#include "absl/debugging/internal/stack_consumption.h"
+#include "absl/memory/memory.h"
+
+using testing::Contains;
+
+#ifdef _WIN32
+#define ABSL_SYMBOLIZE_TEST_NOINLINE __declspec(noinline)
+#else
+#define ABSL_SYMBOLIZE_TEST_NOINLINE ABSL_ATTRIBUTE_NOINLINE
+#endif
+
+// Functions to symbolize. Use C linkage to avoid mangled names.
+extern "C" {
+ABSL_SYMBOLIZE_TEST_NOINLINE void nonstatic_func() {
+  // The next line makes this a unique function to prevent the compiler from
+  // folding identical functions together.
+  volatile int x = __LINE__;
+  static_cast<void>(x);
+  ABSL_BLOCK_TAIL_CALL_OPTIMIZATION();
+}
+
+ABSL_SYMBOLIZE_TEST_NOINLINE static void static_func() {
+  // The next line makes this a unique function to prevent the compiler from
+  // folding identical functions together.
+  volatile int x = __LINE__;
+  static_cast<void>(x);
+  ABSL_BLOCK_TAIL_CALL_OPTIMIZATION();
+}
+}  // extern "C"
+
+struct Foo {
+  static void func(int x);
+};
+
+// A C++ method that should have a mangled name.
+ABSL_SYMBOLIZE_TEST_NOINLINE void Foo::func(int) {
+  // The next line makes this a unique function to prevent the compiler from
+  // folding identical functions together.
+  volatile int x = __LINE__;
+  static_cast<void>(x);
+  ABSL_BLOCK_TAIL_CALL_OPTIMIZATION();
+}
+
+// Create functions that will remain in different text sections in the
+// final binary when linker option "-z,keep-text-section-prefix" is used.
+int ABSL_ATTRIBUTE_SECTION_VARIABLE(.text.unlikely) unlikely_func() {
+  return 0;
+}
+
+int ABSL_ATTRIBUTE_SECTION_VARIABLE(.text.hot) hot_func() {
+  return 0;
+}
+
+int ABSL_ATTRIBUTE_SECTION_VARIABLE(.text.startup) startup_func() {
+  return 0;
+}
+
+int ABSL_ATTRIBUTE_SECTION_VARIABLE(.text.exit) exit_func() {
+  return 0;
+}
+
+int /*ABSL_ATTRIBUTE_SECTION_VARIABLE(.text)*/ regular_func() {
+  return 0;
+}
+
+// Thread-local data may confuse the symbolizer, ensure that it does not.
+// Variable sizes and order are important.
+#if ABSL_PER_THREAD_TLS
+static ABSL_PER_THREAD_TLS_KEYWORD char symbolize_test_thread_small[1];
+static ABSL_PER_THREAD_TLS_KEYWORD char
+    symbolize_test_thread_big[2 * 1024 * 1024];
+#endif
+
+#if !defined(__EMSCRIPTEN__)
+// Used below to hopefully inhibit some compiler/linker optimizations
+// that may remove kHpageTextPadding, kPadding0, and kPadding1 from
+// the binary.
+static volatile bool volatile_bool = false;
+
+// Force the binary to be large enough that a THP .text remap will succeed.
+static constexpr size_t kHpageSize = 1 << 21;
+const char kHpageTextPadding[kHpageSize * 4] ABSL_ATTRIBUTE_SECTION_VARIABLE(
+    .text) = "";
+#endif  // !defined(__EMSCRIPTEN__)
+
+static char try_symbolize_buffer[4096];
+
+// A wrapper function for absl::Symbolize() to make the unit test simple.  The
+// limit must be < sizeof(try_symbolize_buffer).  Returns null if
+// absl::Symbolize() returns false, otherwise returns try_symbolize_buffer with
+// the result of absl::Symbolize().
+static const char *TrySymbolizeWithLimit(void *pc, int limit) {
+  ABSL_RAW_CHECK(limit <= sizeof(try_symbolize_buffer),
+                 "try_symbolize_buffer is too small");
+
+  // Use the heap to facilitate heap and buffer sanitizer tools.
+  auto heap_buffer = absl::make_unique<char[]>(sizeof(try_symbolize_buffer));
+  bool found = absl::Symbolize(pc, heap_buffer.get(), limit);
+  if (found) {
+    ABSL_RAW_CHECK(strnlen(heap_buffer.get(), limit) < limit,
+                   "absl::Symbolize() did not properly terminate the string");
+    strncpy(try_symbolize_buffer, heap_buffer.get(),
+            sizeof(try_symbolize_buffer) - 1);
+    try_symbolize_buffer[sizeof(try_symbolize_buffer) - 1] = '\0';
+  }
+
+  return found ? try_symbolize_buffer : nullptr;
+}
+
+// A wrapper for TrySymbolizeWithLimit(), with a large limit.
+static const char *TrySymbolize(void *pc) {
+  return TrySymbolizeWithLimit(pc, sizeof(try_symbolize_buffer));
+}
+
+#ifdef ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE
+
+TEST(Symbolize, Cached) {
+  // Compilers should give us pointers to them.
+  EXPECT_STREQ("nonstatic_func", TrySymbolize((void *)(&nonstatic_func)));
+
+  // The name of an internal linkage symbol is not specified; allow either a
+  // mangled or an unmangled name here.
+  const char *static_func_symbol = TrySymbolize((void *)(&static_func));
+  EXPECT_TRUE(strcmp("static_func", static_func_symbol) == 0 ||
+              strcmp("static_func()", static_func_symbol) == 0);
+
+  EXPECT_TRUE(nullptr == TrySymbolize(nullptr));
+}
+
+TEST(Symbolize, Truncation) {
+  constexpr char kNonStaticFunc[] = "nonstatic_func";
+  EXPECT_STREQ("nonstatic_func",
+               TrySymbolizeWithLimit((void *)(&nonstatic_func),
+                                     strlen(kNonStaticFunc) + 1));
+  EXPECT_STREQ("nonstatic_...",
+               TrySymbolizeWithLimit((void *)(&nonstatic_func),
+                                     strlen(kNonStaticFunc) + 0));
+  EXPECT_STREQ("nonstatic...",
+               TrySymbolizeWithLimit((void *)(&nonstatic_func),
+                                     strlen(kNonStaticFunc) - 1));
+  EXPECT_STREQ("n...", TrySymbolizeWithLimit((void *)(&nonstatic_func), 5));
+  EXPECT_STREQ("...", TrySymbolizeWithLimit((void *)(&nonstatic_func), 4));
+  EXPECT_STREQ("..", TrySymbolizeWithLimit((void *)(&nonstatic_func), 3));
+  EXPECT_STREQ(".", TrySymbolizeWithLimit((void *)(&nonstatic_func), 2));
+  EXPECT_STREQ("", TrySymbolizeWithLimit((void *)(&nonstatic_func), 1));
+  EXPECT_EQ(nullptr, TrySymbolizeWithLimit((void *)(&nonstatic_func), 0));
+}
+
+TEST(Symbolize, SymbolizeWithDemangling) {
+  Foo::func(100);
+  EXPECT_STREQ("Foo::func()", TrySymbolize((void *)(&Foo::func)));
+}
+
+TEST(Symbolize, SymbolizeSplitTextSections) {
+  EXPECT_STREQ("unlikely_func()", TrySymbolize((void *)(&unlikely_func)));
+  EXPECT_STREQ("hot_func()", TrySymbolize((void *)(&hot_func)));
+  EXPECT_STREQ("startup_func()", TrySymbolize((void *)(&startup_func)));
+  EXPECT_STREQ("exit_func()", TrySymbolize((void *)(&exit_func)));
+  EXPECT_STREQ("regular_func()", TrySymbolize((void *)(&regular_func)));
+}
+
+// Tests that verify that Symbolize stack footprint is within some limit.
+#ifdef ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
+
+static void *g_pc_to_symbolize;
+static char g_symbolize_buffer[4096];
+static char *g_symbolize_result;
+
+static void SymbolizeSignalHandler(int signo) {
+  if (absl::Symbolize(g_pc_to_symbolize, g_symbolize_buffer,
+                      sizeof(g_symbolize_buffer))) {
+    g_symbolize_result = g_symbolize_buffer;
+  } else {
+    g_symbolize_result = nullptr;
+  }
+}
+
+// Call Symbolize and figure out the stack footprint of this call.
+static const char *SymbolizeStackConsumption(void *pc, int *stack_consumed) {
+  g_pc_to_symbolize = pc;
+  *stack_consumed = absl::debugging_internal::GetSignalHandlerStackConsumption(
+      SymbolizeSignalHandler);
+  return g_symbolize_result;
+}
+
+static int GetStackConsumptionUpperLimit() {
+  // Symbolize stack consumption should be within 2kB.
+  int stack_consumption_upper_limit = 2048;
+#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
+    defined(THREAD_SANITIZER)
+  // Account for sanitizer instrumentation requiring additional stack space.
+  stack_consumption_upper_limit *= 5;
+#endif
+  return stack_consumption_upper_limit;
+}
+
+TEST(Symbolize, SymbolizeStackConsumption) {
+  int stack_consumed = 0;
+
+  const char *symbol =
+      SymbolizeStackConsumption((void *)(&nonstatic_func), &stack_consumed);
+  EXPECT_STREQ("nonstatic_func", symbol);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, GetStackConsumptionUpperLimit());
+
+  // The name of an internal linkage symbol is not specified; allow either a
+  // mangled or an unmangled name here.
+  symbol = SymbolizeStackConsumption((void *)(&static_func), &stack_consumed);
+  EXPECT_TRUE(strcmp("static_func", symbol) == 0 ||
+              strcmp("static_func()", symbol) == 0);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, GetStackConsumptionUpperLimit());
+}
+
+TEST(Symbolize, SymbolizeWithDemanglingStackConsumption) {
+  Foo::func(100);
+  int stack_consumed = 0;
+
+  const char *symbol =
+      SymbolizeStackConsumption((void *)(&Foo::func), &stack_consumed);
+
+  EXPECT_STREQ("Foo::func()", symbol);
+  EXPECT_GT(stack_consumed, 0);
+  EXPECT_LT(stack_consumed, GetStackConsumptionUpperLimit());
+}
+
+#endif  // ABSL_INTERNAL_HAVE_DEBUGGING_STACK_CONSUMPTION
+
+// Use a 64K page size for PPC.
+const size_t kPageSize = 64 << 10;
+// We place a read-only symbols into the .text section and verify that we can
+// symbolize them and other symbols after remapping them.
+const char kPadding0[kPageSize * 4] ABSL_ATTRIBUTE_SECTION_VARIABLE(.text) =
+    "";
+const char kPadding1[kPageSize * 4] ABSL_ATTRIBUTE_SECTION_VARIABLE(.text) =
+    "";
+
+static int FilterElfHeader(struct dl_phdr_info *info, size_t size, void *data) {
+  for (int i = 0; i < info->dlpi_phnum; i++) {
+    if (info->dlpi_phdr[i].p_type == PT_LOAD &&
+        info->dlpi_phdr[i].p_flags == (PF_R | PF_X)) {
+      const void *const vaddr =
+          absl::bit_cast<void *>(info->dlpi_addr + info->dlpi_phdr[i].p_vaddr);
+      const auto segsize = info->dlpi_phdr[i].p_memsz;
+
+      const char *self_exe;
+      if (info->dlpi_name != nullptr && info->dlpi_name[0] != '\0') {
+        self_exe = info->dlpi_name;
+      } else {
+        self_exe = "/proc/self/exe";
+      }
+
+      absl::debugging_internal::RegisterFileMappingHint(
+          vaddr, reinterpret_cast<const char *>(vaddr) + segsize,
+          info->dlpi_phdr[i].p_offset, self_exe);
+
+      return 1;
+    }
+  }
+
+  return 1;
+}
+
+TEST(Symbolize, SymbolizeWithMultipleMaps) {
+  // Force kPadding0 and kPadding1 to be linked in.
+  if (volatile_bool) {
+    ABSL_RAW_LOG(INFO, "%s", kPadding0);
+    ABSL_RAW_LOG(INFO, "%s", kPadding1);
+  }
+
+  // Verify we can symbolize everything.
+  char buf[512];
+  memset(buf, 0, sizeof(buf));
+  absl::Symbolize(kPadding0, buf, sizeof(buf));
+  EXPECT_STREQ("kPadding0", buf);
+
+  memset(buf, 0, sizeof(buf));
+  absl::Symbolize(kPadding1, buf, sizeof(buf));
+  EXPECT_STREQ("kPadding1", buf);
+
+  // Specify a hint for the executable segment.
+  dl_iterate_phdr(FilterElfHeader, nullptr);
+
+  // Reload at least one page out of kPadding0, kPadding1
+  const char *ptrs[] = {kPadding0, kPadding1};
+
+  for (const char *ptr : ptrs) {
+    const int kMapFlags = MAP_ANONYMOUS | MAP_PRIVATE;
+    void *addr = mmap(nullptr, kPageSize, PROT_READ, kMapFlags, 0, 0);
+    ASSERT_NE(addr, MAP_FAILED);
+
+    // kPadding[0-1] is full of zeroes, so we can remap anywhere within it, but
+    // we ensure there is at least a full page of padding.
+    void *remapped = reinterpret_cast<void *>(
+        reinterpret_cast<uintptr_t>(ptr + kPageSize) & ~(kPageSize - 1ULL));
+
+    const int kMremapFlags = (MREMAP_MAYMOVE | MREMAP_FIXED);
+    void *ret = mremap(addr, kPageSize, kPageSize, kMremapFlags, remapped);
+    ASSERT_NE(ret, MAP_FAILED);
+  }
+
+  // Invalidate the symbolization cache so we are forced to rely on the hint.
+  absl::Symbolize(nullptr, buf, sizeof(buf));
+
+  // Verify we can still symbolize.
+  const char *expected[] = {"kPadding0", "kPadding1"};
+  const size_t offsets[] = {0, kPageSize, 2 * kPageSize, 3 * kPageSize};
+
+  for (int i = 0; i < 2; i++) {
+    for (size_t offset : offsets) {
+      memset(buf, 0, sizeof(buf));
+      absl::Symbolize(ptrs[i] + offset, buf, sizeof(buf));
+      EXPECT_STREQ(expected[i], buf);
+    }
+  }
+}
+
+// Appends string(*args->arg) to args->symbol_buf.
+static void DummySymbolDecorator(
+    const absl::debugging_internal::SymbolDecoratorArgs *args) {
+  std::string *message = static_cast<std::string *>(args->arg);
+  strncat(args->symbol_buf, message->c_str(),
+          args->symbol_buf_size - strlen(args->symbol_buf) - 1);
+}
+
+TEST(Symbolize, InstallAndRemoveSymbolDecorators) {
+  int ticket_a;
+  std::string a_message("a");
+  EXPECT_GE(ticket_a = absl::debugging_internal::InstallSymbolDecorator(
+                DummySymbolDecorator, &a_message),
+            0);
+
+  int ticket_b;
+  std::string b_message("b");
+  EXPECT_GE(ticket_b = absl::debugging_internal::InstallSymbolDecorator(
+                DummySymbolDecorator, &b_message),
+            0);
+
+  int ticket_c;
+  std::string c_message("c");
+  EXPECT_GE(ticket_c = absl::debugging_internal::InstallSymbolDecorator(
+                DummySymbolDecorator, &c_message),
+            0);
+
+  char *address = reinterpret_cast<char *>(1);
+  EXPECT_STREQ("abc", TrySymbolize(address++));
+
+  EXPECT_TRUE(absl::debugging_internal::RemoveSymbolDecorator(ticket_b));
+
+  EXPECT_STREQ("ac", TrySymbolize(address++));
+
+  // Cleanup: remove all remaining decorators so other stack traces don't
+  // get mystery "ac" decoration.
+  EXPECT_TRUE(absl::debugging_internal::RemoveSymbolDecorator(ticket_a));
+  EXPECT_TRUE(absl::debugging_internal::RemoveSymbolDecorator(ticket_c));
+}
+
+// Some versions of Clang with optimizations enabled seem to be able
+// to optimize away the .data section if no variables live in the
+// section. This variable should get placed in the .data section, and
+// the test below checks for the existence of a .data section.
+static int in_data_section = 1;
+
+TEST(Symbolize, ForEachSection) {
+  int fd = TEMP_FAILURE_RETRY(open("/proc/self/exe", O_RDONLY));
+  ASSERT_NE(fd, -1);
+
+  std::vector<std::string> sections;
+  ASSERT_TRUE(absl::debugging_internal::ForEachSection(
+      fd, [&sections](const std::string &name, const ElfW(Shdr) &) {
+        sections.push_back(name);
+        return true;
+      }));
+
+  // Check for the presence of common section names.
+  EXPECT_THAT(sections, Contains(".text"));
+  EXPECT_THAT(sections, Contains(".rodata"));
+  EXPECT_THAT(sections, Contains(".bss"));
+  ++in_data_section;
+  EXPECT_THAT(sections, Contains(".data"));
+
+  close(fd);
+}
+
+// x86 specific tests.  Uses some inline assembler.
+extern "C" {
+inline void *ABSL_ATTRIBUTE_ALWAYS_INLINE inline_func() {
+  void *pc = nullptr;
+#if defined(__i386__)
+  __asm__ __volatile__("call 1f;\n 1: pop %[PC]" : [ PC ] "=r"(pc));
+#elif defined(__x86_64__)
+  __asm__ __volatile__("leaq 0(%%rip),%[PC];\n" : [ PC ] "=r"(pc));
+#endif
+  return pc;
+}
+
+void *ABSL_ATTRIBUTE_NOINLINE non_inline_func() {
+  void *pc = nullptr;
+#if defined(__i386__)
+  __asm__ __volatile__("call 1f;\n 1: pop %[PC]" : [ PC ] "=r"(pc));
+#elif defined(__x86_64__)
+  __asm__ __volatile__("leaq 0(%%rip),%[PC];\n" : [ PC ] "=r"(pc));
+#endif
+  return pc;
+}
+
+void ABSL_ATTRIBUTE_NOINLINE TestWithPCInsideNonInlineFunction() {
+#if defined(ABSL_HAVE_ATTRIBUTE_NOINLINE) && \
+    (defined(__i386__) || defined(__x86_64__))
+  void *pc = non_inline_func();
+  const char *symbol = TrySymbolize(pc);
+  ABSL_RAW_CHECK(symbol != nullptr, "TestWithPCInsideNonInlineFunction failed");
+  ABSL_RAW_CHECK(strcmp(symbol, "non_inline_func") == 0,
+                 "TestWithPCInsideNonInlineFunction failed");
+  std::cout << "TestWithPCInsideNonInlineFunction passed" << std::endl;
+#endif
+}
+
+void ABSL_ATTRIBUTE_NOINLINE TestWithPCInsideInlineFunction() {
+#if defined(ABSL_HAVE_ATTRIBUTE_ALWAYS_INLINE) && \
+    (defined(__i386__) || defined(__x86_64__))
+  void *pc = inline_func();  // Must be inlined.
+  const char *symbol = TrySymbolize(pc);
+  ABSL_RAW_CHECK(symbol != nullptr, "TestWithPCInsideInlineFunction failed");
+  ABSL_RAW_CHECK(strcmp(symbol, __FUNCTION__) == 0,
+                 "TestWithPCInsideInlineFunction failed");
+  std::cout << "TestWithPCInsideInlineFunction passed" << std::endl;
+#endif
+}
+}
+
+// Test with a return address.
+void ABSL_ATTRIBUTE_NOINLINE TestWithReturnAddress() {
+#if defined(ABSL_HAVE_ATTRIBUTE_NOINLINE)
+  void *return_address = __builtin_return_address(0);
+  const char *symbol = TrySymbolize(return_address);
+  ABSL_RAW_CHECK(symbol != nullptr, "TestWithReturnAddress failed");
+  ABSL_RAW_CHECK(strcmp(symbol, "main") == 0, "TestWithReturnAddress failed");
+  std::cout << "TestWithReturnAddress passed" << std::endl;
+#endif
+}
+
+#elif defined(_WIN32)
+#if !defined(ABSL_CONSUME_DLL)
+
+TEST(Symbolize, Basics) {
+  EXPECT_STREQ("nonstatic_func", TrySymbolize((void *)(&nonstatic_func)));
+
+  // The name of an internal linkage symbol is not specified; allow either a
+  // mangled or an unmangled name here.
+  const char *static_func_symbol = TrySymbolize((void *)(&static_func));
+  ASSERT_TRUE(static_func_symbol != nullptr);
+  EXPECT_TRUE(strstr(static_func_symbol, "static_func") != nullptr);
+
+  EXPECT_TRUE(nullptr == TrySymbolize(nullptr));
+}
+
+TEST(Symbolize, Truncation) {
+  constexpr char kNonStaticFunc[] = "nonstatic_func";
+  EXPECT_STREQ("nonstatic_func",
+               TrySymbolizeWithLimit((void *)(&nonstatic_func),
+                                     strlen(kNonStaticFunc) + 1));
+  EXPECT_STREQ("nonstatic_...",
+               TrySymbolizeWithLimit((void *)(&nonstatic_func),
+                                     strlen(kNonStaticFunc) + 0));
+  EXPECT_STREQ("nonstatic...",
+               TrySymbolizeWithLimit((void *)(&nonstatic_func),
+                                     strlen(kNonStaticFunc) - 1));
+  EXPECT_STREQ("n...", TrySymbolizeWithLimit((void *)(&nonstatic_func), 5));
+  EXPECT_STREQ("...", TrySymbolizeWithLimit((void *)(&nonstatic_func), 4));
+  EXPECT_STREQ("..", TrySymbolizeWithLimit((void *)(&nonstatic_func), 3));
+  EXPECT_STREQ(".", TrySymbolizeWithLimit((void *)(&nonstatic_func), 2));
+  EXPECT_STREQ("", TrySymbolizeWithLimit((void *)(&nonstatic_func), 1));
+  EXPECT_EQ(nullptr, TrySymbolizeWithLimit((void *)(&nonstatic_func), 0));
+}
+
+TEST(Symbolize, SymbolizeWithDemangling) {
+  const char *result = TrySymbolize((void *)(&Foo::func));
+  ASSERT_TRUE(result != nullptr);
+  EXPECT_TRUE(strstr(result, "Foo::func") != nullptr) << result;
+}
+
+#endif  // !defined(ABSL_CONSUME_DLL)
+#else  // Symbolizer unimplemented
+
+TEST(Symbolize, Unimplemented) {
+  char buf[64];
+  EXPECT_FALSE(absl::Symbolize((void *)(&nonstatic_func), buf, sizeof(buf)));
+  EXPECT_FALSE(absl::Symbolize((void *)(&static_func), buf, sizeof(buf)));
+  EXPECT_FALSE(absl::Symbolize((void *)(&Foo::func), buf, sizeof(buf)));
+}
+
+#endif
+
+int main(int argc, char **argv) {
+#if !defined(__EMSCRIPTEN__)
+  // Make sure kHpageTextPadding is linked into the binary.
+  if (volatile_bool) {
+    ABSL_RAW_LOG(INFO, "%s", kHpageTextPadding);
+  }
+#endif  // !defined(__EMSCRIPTEN__)
+
+#if ABSL_PER_THREAD_TLS
+  // Touch the per-thread variables.
+  symbolize_test_thread_small[0] = 0;
+  symbolize_test_thread_big[0] = 0;
+#endif
+
+  absl::InitializeSymbolizer(argv[0]);
+  testing::InitGoogleTest(&argc, argv);
+
+#ifdef ABSL_INTERNAL_HAVE_ELF_SYMBOLIZE
+  TestWithPCInsideInlineFunction();
+  TestWithPCInsideNonInlineFunction();
+  TestWithReturnAddress();
+#endif
+
+  return RUN_ALL_TESTS();
+}
diff --git a/third_party/abseil_cpp/absl/debugging/symbolize_unimplemented.inc b/third_party/abseil_cpp/absl/debugging/symbolize_unimplemented.inc
new file mode 100644
index 000000000000..db24456b0afa
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/symbolize_unimplemented.inc
@@ -0,0 +1,40 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <cstdint>
+
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace debugging_internal {
+
+int InstallSymbolDecorator(SymbolDecorator, void*) { return -1; }
+bool RemoveSymbolDecorator(int) { return false; }
+bool RemoveAllSymbolDecorators(void) { return false; }
+bool RegisterFileMappingHint(const void *, const void *, uint64_t, const char *) {
+  return false;
+}
+bool GetFileMappingHint(const void **, const void **, uint64_t *, const char **) {
+  return false;
+}
+
+}  // namespace debugging_internal
+
+void InitializeSymbolizer(const char*) {}
+bool Symbolize(const void *, char *, int) { return false; }
+
+ABSL_NAMESPACE_END
+}  // namespace absl
diff --git a/third_party/abseil_cpp/absl/debugging/symbolize_win32.inc b/third_party/abseil_cpp/absl/debugging/symbolize_win32.inc
new file mode 100644
index 000000000000..c3df46f606c2
--- /dev/null
+++ b/third_party/abseil_cpp/absl/debugging/symbolize_win32.inc
@@ -0,0 +1,81 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// See "Retrieving Symbol Information by Address":
+// https://msdn.microsoft.com/en-us/library/windows/desktop/ms680578(v=vs.85).aspx
+
+#include <windows.h>
+
+// MSVC header dbghelp.h has a warning for an ignored typedef.
+#pragma warning(push)
+#pragma warning(disable:4091)
+#include <dbghelp.h>
+#pragma warning(pop)
+
+#pragma comment(lib, "dbghelp.lib")
+
+#include <algorithm>
+#include <cstring>
+
+#include "absl/base/internal/raw_logging.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+static HANDLE process = NULL;
+
+void InitializeSymbolizer(const char*) {
+  if (process != nullptr) {
+    return;
+  }
+  process = GetCurrentProcess();
+
+  // Symbols are not loaded until a reference is made requiring the
+  // symbols be loaded. This is the fastest, most efficient way to use
+  // the symbol handler.
+  SymSetOptions(SYMOPT_DEFERRED_LOADS | SYMOPT_UNDNAME);
+  if (!SymInitialize(process, nullptr, true)) {
+    // GetLastError() returns a Win32 DWORD, but we assign to
+    // unsigned long long to simplify the ABSL_RAW_LOG case below.  The uniform
+    // initialization guarantees this is not a narrowing conversion.
+    const unsigned long long error{GetLastError()};  // NOLINT(runtime/int)
+    ABSL_RAW_LOG(FATAL, "SymInitialize() failed: %llu", error);
+  }
+}
+
+bool Symbolize(const void* pc, char* out, int out_size) {
+  if (out_size <= 0) {
+    return false;
+  }
+  alignas(SYMBOL_INFO) char buf[sizeof(SYMBOL_INFO) + MAX_SYM_NAME];
+  SYMBOL_INFO* symbol = reinterpret_cast<SYMBOL_INFO*>(buf);
+  symbol->SizeOfStruct = sizeof(SYMBOL_INFO);
+  symbol->MaxNameLen = MAX_SYM_NAME;
+  if (!SymFromAddr(process, reinterpret_cast<DWORD64>(pc), nullptr, symbol)) {
+    return false;
+  }
+  strncpy(out, symbol->Name, out_size);
+  if (out[out_size - 1] != '\0') {
+    // strncpy() does not '\0' terminate when it truncates.
+    static constexpr char kEllipsis[] = "...";
+    int ellipsis_size =
+        std::min<int>(sizeof(kEllipsis) - 1, out_size - 1);
+    memcpy(out + out_size - ellipsis_size - 1, kEllipsis, ellipsis_size);
+    out[out_size - 1] = '\0';
+  }
+  return true;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl