vdso_support.cc | Explore in Territory

// 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

#if !defined(__has_include)
#define __has_include …
#endif

#include <errno.h>
#include <fcntl.h>
#if __has_include(<syscall.h>)
#include <syscall.h>
#elif __has_include(<sys/syscall.h>)
#include <sys/syscall.h>
#endif
#include <unistd.h>

#if !defined(__UCLIBC__) && defined(__GLIBC__) && \
    (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 16))
#define ABSL_HAVE_GETAUXVAL
#endif

#ifdef ABSL_HAVE_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 …
#endif

#if defined(__NetBSD__)
using Elf32_auxv_t = Aux32Info;
using Elf64_auxv_t = Aux64Info;
#endif
#if defined(__FreeBSD__)
#if defined(__ELF_WORD_SIZE) && __ELF_WORD_SIZE == 64
using Elf64_auxv_t = Elf64_Auxinfo;
#endif
using Elf32_auxv_t = Elf32_Auxinfo;
#endif

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace debugging_internal {

ABSL_CONST_INIT
std::atomic<const void *> VDSOSupport::vdso_base_(
    debugging_internal::ElfMemImage::kInvalidBase);

ABSL_CONST_INIT 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.
    : … { … }

// 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 void *VDSOSupport::SetBase(const void *base) { … }

bool VDSOSupport::LookupSymbol(const char *name,
                               const char *version,
                               int type,
                               SymbolInfo *info) const { … }

bool VDSOSupport::LookupSymbolByAddress(const void *address,
                                        SymbolInfo *info_out) const { … }

// NOLINT on 'long' because this routine mimics kernel api.
long VDSOSupport::GetCPUViaSyscall(unsigned *cpu,  // NOLINT(runtime/int)
                                   void *, void *) { … }

// Use fast __vdso_getcpu if available.
long VDSOSupport::InitAndGetCPU(unsigned *cpu,  // NOLINT(runtime/int)
                                void *x, void *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() { … }

}  // namespace debugging_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_HAVE_VDSO_SUPPORT
chromium/third_party/abseil-cpp/absl/debugging/internal/vdso_support.cc
