diff options
Diffstat (limited to 'third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc')
-rw-r--r-- | third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc | 139 |
1 files changed, 0 insertions, 139 deletions
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 deleted file mode 100644 index 329c285f3b58..000000000000 --- a/third_party/abseil_cpp/absl/debugging/internal/address_is_readable.cc +++ /dev/null @@ -1,139 +0,0 @@ -// 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_acquire); - 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_release, - 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_acquire); - } - 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_release, - std::memory_order_relaxed); - } - } while (errno == EBADF); - return bytes_written == 1; -} - -} // namespace debugging_internal -ABSL_NAMESPACE_END -} // namespace absl - -#endif |