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1 // Copyright 2008 Google Inc. All Rights Reserved. | 1 // Copyright 2008 Google Inc. All Rights Reserved. |
2 // Author: ppluzhnikov@google.com (Paul Pluzhnikov) | 2 // Author: ppluzhnikov@google.com (Paul Pluzhnikov) |
3 // | 3 // |
4 // Allow dynamic symbol lookup in the kernel VDSO page. | 4 // Allow dynamic symbol lookup in the kernel VDSO page. |
5 // | 5 // |
6 // VDSO stands for "Virtual Dynamic Shared Object" -- a page of | 6 // VDSO stands for "Virtual Dynamic Shared Object" -- a page of |
7 // executable code, which looks like a shared library, but doesn't | 7 // executable code, which looks like a shared library, but doesn't |
8 // necessarily exist anywhere on disk, and which gets mmap()ed into | 8 // necessarily exist anywhere on disk, and which gets mmap()ed into |
9 // every process by kernels which support VDSO, such as 2.6.x for 32-bit | 9 // every process by kernels which support VDSO, such as 2.6.x for 32-bit |
10 // executables, and 2.6.24 and above for 64-bit executables. | 10 // executables, and 2.6.24 and above for 64-bit executables. |
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23 // fn = reinterpret_cast<FN>(info.address); | 23 // fn = reinterpret_cast<FN>(info.address); |
24 // } | 24 // } |
25 | 25 |
26 #ifndef BASE_VDSO_SUPPORT_H_ | 26 #ifndef BASE_VDSO_SUPPORT_H_ |
27 #define BASE_VDSO_SUPPORT_H_ | 27 #define BASE_VDSO_SUPPORT_H_ |
28 | 28 |
29 #include <config.h> | 29 #include <config.h> |
30 #ifdef HAVE_FEATURES_H | 30 #ifdef HAVE_FEATURES_H |
31 #include <features.h> // for __GLIBC__ | 31 #include <features.h> // for __GLIBC__ |
32 #endif | 32 #endif |
| 33 #include "base/basictypes.h" |
33 | 34 |
34 // Maybe one day we can rewrite this file not to require the elf | 35 // Maybe one day we can rewrite this file not to require the elf |
35 // symbol extensions in glibc, but for right now we need them. | 36 // symbol extensions in glibc, but for right now we need them. |
36 #if defined(__ELF__) && defined(__GLIBC__) | 37 #if defined(__ELF__) && defined(__GLIBC__) |
37 | 38 |
38 #define HAVE_VDSO_SUPPORT 1 | 39 #define HAVE_VDSO_SUPPORT 1 |
39 | 40 |
40 #include <stdlib.h> // for NULL | 41 #include <stdlib.h> // for NULL |
41 #include <link.h> // for ElfW | 42 #include <link.h> // for ElfW |
42 #include "base/basictypes.h" | |
43 | 43 |
44 namespace base { | 44 namespace base { |
45 | 45 |
46 // NOTE: this class may be used from within tcmalloc, and can not | 46 // NOTE: this class may be used from within tcmalloc, and can not |
47 // use any memory allocation routines. | 47 // use any memory allocation routines. |
48 class VDSOSupport { | 48 class VDSOSupport { |
49 public: | 49 public: |
50 // Sentinel: there could never be a VDSO at this address. | 50 // Sentinel: there could never be a VDSO at this address. |
51 static const void *const kInvalidBase; | 51 static const void *const kInvalidBase; |
52 | 52 |
53 // Information about a single vdso symbol. | 53 // Information about a single vdso symbol. |
54 // All pointers are into .dynsym, .dynstr, or .text of the VDSO. | 54 // All pointers are into .dynsym, .dynstr, or .text of the VDSO. |
55 // Do not free() them or modify through them. | 55 // Do not free() them or modify through them. |
56 struct SymbolInfo { | 56 struct SymbolInfo { |
57 const char *name; // E.g. "__vdso_getcpu" | 57 const char *name; // E.g. "__vdso_getcpu" |
58 const char *version; // E.g. "LINUX_2.6", could be "" | 58 const char *version; // E.g. "LINUX_2.6", could be "" |
59 // for unversioned symbol. | 59 // for unversioned symbol. |
60 const void *address; // Relocated symbol address. | 60 const void *address; // Relocated symbol address. |
61 const ElfW(Sym) *symbol; // Symbol in the dynamic symbol table. | 61 const ElfW(Sym) *symbol; // Symbol in the dynamic symbol table. |
62 }; | 62 }; |
63 | 63 |
64 // Supports iteration over all dynamic symbols. | 64 // Supports iteration over all dynamic symbols. |
65 class SymbolIterator { | 65 class SymbolIterator { |
66 public: | 66 public: |
67 friend struct VDSOSupport; | 67 friend class VDSOSupport; |
68 const SymbolInfo *operator->() const; | 68 const SymbolInfo *operator->() const; |
69 const SymbolInfo &operator*() const; | 69 const SymbolInfo &operator*() const; |
70 SymbolIterator& operator++(); | 70 SymbolIterator& operator++(); |
71 bool operator!=(const SymbolIterator &rhs) const; | 71 bool operator!=(const SymbolIterator &rhs) const; |
72 bool operator==(const SymbolIterator &rhs) const; | 72 bool operator==(const SymbolIterator &rhs) const; |
73 private: | 73 private: |
74 SymbolIterator(const void *const image, int index); | 74 SymbolIterator(const void *const image, int index); |
75 void Update(int incr); | 75 void Update(int incr); |
76 SymbolInfo info_; | 76 SymbolInfo info_; |
77 int index_; | 77 int index_; |
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140 | 140 |
141 // image_ represents VDSO ELF image in memory. | 141 // image_ represents VDSO ELF image in memory. |
142 // image_.ehdr_ == NULL implies there is no VDSO. | 142 // image_.ehdr_ == NULL implies there is no VDSO. |
143 ElfMemImage image_; | 143 ElfMemImage image_; |
144 | 144 |
145 // Cached value of auxv AT_SYSINFO_EHDR, computed once. | 145 // Cached value of auxv AT_SYSINFO_EHDR, computed once. |
146 // This is a tri-state: | 146 // This is a tri-state: |
147 // kInvalidBase => value hasn't been determined yet. | 147 // kInvalidBase => value hasn't been determined yet. |
148 // 0 => there is no VDSO. | 148 // 0 => there is no VDSO. |
149 // else => vma of VDSO Elf{32,64}_Ehdr. | 149 // else => vma of VDSO Elf{32,64}_Ehdr. |
| 150 // |
| 151 // When testing with mock VDSO, low bit is set. |
| 152 // The low bit is always available because vdso_base_ is |
| 153 // page-aligned. |
150 static const void *vdso_base_; | 154 static const void *vdso_base_; |
151 | 155 |
152 // NOLINT on 'long' because these routines mimic kernel api. | 156 // NOLINT on 'long' because these routines mimic kernel api. |
153 // The 'cache' parameter may be used by some versions of the kernel, | 157 // The 'cache' parameter may be used by some versions of the kernel, |
154 // and should be NULL or point to a static buffer containing at | 158 // and should be NULL or point to a static buffer containing at |
155 // least two 'long's. | 159 // least two 'long's. |
156 static long InitAndGetCPU(unsigned *cpu, void *cache, // NOLINT 'long'. | 160 static long InitAndGetCPU(unsigned *cpu, void *cache, // NOLINT 'long'. |
157 void *unused); | 161 void *unused); |
158 static long GetCPUViaSyscall(unsigned *cpu, void *cache, // NOLINT 'long'. | 162 static long GetCPUViaSyscall(unsigned *cpu, void *cache, // NOLINT 'long'. |
159 void *unused); | 163 void *unused); |
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173 // Return current CPU, using (fast) __vdso_getcpu@LINUX_2.6 if present, | 177 // Return current CPU, using (fast) __vdso_getcpu@LINUX_2.6 if present, |
174 // otherwise use syscall(SYS_getcpu,...). | 178 // otherwise use syscall(SYS_getcpu,...). |
175 // May return -1 with errno == ENOSYS if the kernel doesn't | 179 // May return -1 with errno == ENOSYS if the kernel doesn't |
176 // support SYS_getcpu. | 180 // support SYS_getcpu. |
177 int GetCPU(); | 181 int GetCPU(); |
178 } // namespace base | 182 } // namespace base |
179 | 183 |
180 #endif // __ELF__ and __GLIBC__ | 184 #endif // __ELF__ and __GLIBC__ |
181 | 185 |
182 #endif // BASE_VDSO_SUPPORT_H_ | 186 #endif // BASE_VDSO_SUPPORT_H_ |
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