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Diffstat (limited to 'absl/debugging/internal/vdso_support.h')
| -rw-r--r-- | absl/debugging/internal/vdso_support.h | 155 |
1 files changed, 155 insertions, 0 deletions
diff --git a/absl/debugging/internal/vdso_support.h b/absl/debugging/internal/vdso_support.h new file mode 100644 index 000000000000..a6a7a17794e3 --- /dev/null +++ b/absl/debugging/internal/vdso_support.h @@ -0,0 +1,155 @@ +// +// 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 +// +// http://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/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 { +namespace debug_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. + 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 debug_internal +} // namespace absl + +#endif // ABSL_HAVE_ELF_MEM_IMAGE + +#endif // ABSL_DEBUGGING_INTERNAL_VDSO_SUPPORT_H_ |