138 lines
5.1 KiB
C++
138 lines
5.1 KiB
C++
// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
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// Copyright (c) 2008, Google Inc.
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// ---
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// Author: Paul Pluzhnikov
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//
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// Allow dynamic symbol lookup in the kernel VDSO page.
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//
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// VDSO stands for "Virtual Dynamic Shared Object" -- a page of
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// executable code, which looks like a shared library, but doesn't
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// necessarily exist anywhere on disk, and which gets mmap()ed into
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// every process by kernels which support VDSO, such as 2.6.x for 32-bit
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// executables, and 2.6.24 and above for 64-bit executables.
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//
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// More details could be found here:
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// http://www.trilithium.com/johan/2005/08/linux-gate/
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//
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// VDSOSupport -- a class representing kernel VDSO (if present).
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//
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// Example usage:
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// VDSOSupport vdso;
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// VDSOSupport::SymbolInfo info;
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// typedef (*FN)(unsigned *, void *, void *);
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// FN fn = NULL;
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// if (vdso.LookupSymbol("__vdso_getcpu", "LINUX_2.6", STT_FUNC, &info)) {
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// fn = reinterpret_cast<FN>(info.address);
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// }
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#ifndef BASE_VDSO_SUPPORT_H_
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#define BASE_VDSO_SUPPORT_H_
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#include <config.h>
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#include "base/basictypes.h"
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#include "base/elf_mem_image.h"
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#ifdef HAVE_ELF_MEM_IMAGE
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// Enable VDSO support only for the architectures/operating systems that
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// support it.
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#if defined(__linux__) && (defined(__i386__) || defined(__PPC__))
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#define HAVE_VDSO_SUPPORT 1
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#endif
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#include <stdlib.h> // for NULL
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namespace base {
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// NOTE: this class may be used from within tcmalloc, and can not
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// use any memory allocation routines.
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class VDSOSupport {
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public:
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VDSOSupport();
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typedef ElfMemImage::SymbolInfo SymbolInfo;
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typedef ElfMemImage::SymbolIterator SymbolIterator;
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// Answers whether we have a vdso at all.
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bool IsPresent() const { return image_.IsPresent(); }
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// Allow to iterate over all VDSO symbols.
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SymbolIterator begin() const { return image_.begin(); }
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SymbolIterator end() const { return image_.end(); }
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// Look up versioned dynamic symbol in the kernel VDSO.
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// Returns false if VDSO is not present, or doesn't contain given
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// symbol/version/type combination.
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// If info_out != NULL, additional details are filled in.
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bool LookupSymbol(const char *name, const char *version,
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int symbol_type, SymbolInfo *info_out) const;
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// Find info about symbol (if any) which overlaps given address.
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// Returns true if symbol was found; false if VDSO isn't present
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// or doesn't have a symbol overlapping given address.
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// If info_out != NULL, additional details are filled in.
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bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
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// Used only for testing. Replace real VDSO base with a mock.
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// Returns previous value of vdso_base_. After you are done testing,
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// you are expected to call SetBase() with previous value, in order to
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// reset state to the way it was.
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const void *SetBase(const void *s);
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// Computes vdso_base_ and returns it. Should be called as early as
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// possible; before any thread creation, chroot or setuid.
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static const void *Init();
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private:
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// image_ represents VDSO ELF image in memory.
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// image_.ehdr_ == NULL implies there is no VDSO.
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ElfMemImage image_;
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// Cached value of auxv AT_SYSINFO_EHDR, computed once.
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// This is a tri-state:
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// kInvalidBase => value hasn't been determined yet.
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// 0 => there is no VDSO.
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// else => vma of VDSO Elf{32,64}_Ehdr.
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//
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// When testing with mock VDSO, low bit is set.
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// The low bit is always available because vdso_base_ is
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// page-aligned.
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static const void *vdso_base_;
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DISALLOW_COPY_AND_ASSIGN(VDSOSupport);
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};
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} // namespace base
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#endif // HAVE_ELF_MEM_IMAGE
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#endif // BASE_VDSO_SUPPORT_H_
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