chromium/third_party/abseil-cpp/absl/debugging/internal/vdso_support.h

//
// 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 …
#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 { … };

// 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_