1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
|
// 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 "base/basictypes.h"
#include "base/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:
// 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 const void *vdso_base_;
DISALLOW_COPY_AND_ASSIGN(VDSOSupport);
};
} // namespace base
#endif // HAVE_ELF_MEM_IMAGE
#endif // BASE_VDSO_SUPPORT_H_
|
