tvl-depot/absl/debugging/internal/vdso_support.h
Abseil Team 12bc53e031 Export of internal Abseil changes
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c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro <dmauro@google.com>:

Remove a floating point division by zero test.

This isn't testing behavior related to the library, and MSVC warns
about it in opt mode.

PiperOrigin-RevId: 285220804

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68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental <rogeeff@google.com>:

This CL introduces following changes to the class FlagImpl:
* We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately.
* CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now.
* Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call.
* We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced.

PiperOrigin-RevId: 285132636

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ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck <shreck@google.com>:

Change null-term* (and nul-term*) to NUL-term* in comments

PiperOrigin-RevId: 285036610

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729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro <dmauro@google.com>:

Use the Posix implementation of thread identity on MinGW.
Some versions of MinGW suffer from thread_local bugs.

PiperOrigin-RevId: 285022920

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39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon <gfalcon@google.com>:

Implementation detail change.

Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil.

PiperOrigin-RevId: 285012012
GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c
Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1
2019-12-12 15:37:13 -05:00

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5.7 KiB
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//
// 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_