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#pragma once
// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// ---
// Author: Paul Pluzhnikov
//
// 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 = NULL;
// if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) {
// fn = reinterpret_cast<FN>(info.address);
// }
#ifndef BASE_VDSO_SUPPORT_H_
#define BASE_VDSO_SUPPORT_H_
#include "config.h"
#include "elf_mem_image.h"
#ifdef HAVE_ELF_MEM_IMAGE
#define HAVE_VDSO_SUPPORT 1
#include <stdlib.h> // for NULL
namespace base {
// 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;
// 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 != NULL, 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 != NULL, 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_ == NULL implies there is no VDSO.
ElfMemImage image_;
// Cached value of auxv AT_SYSINFO_EHDR, computed once.
// This is a tri-state:
// 0 => value hasn't been determined yet.
// kInvalidBase => 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 const void *vdso_base_;
DISALLOW_COPY_AND_ASSIGN(VDSOSupport);
};
} // namespace base
#endif // HAVE_ELF_MEM_IMAGE
#endif // BASE_VDSO_SUPPORT_H_
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