1 /* 2 * Copyright 2017 The Abseil Authors. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * https://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 // Allow dynamic symbol lookup for in-memory Elf images. 18 19 #ifndef ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_ 20 #define ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_ 21 22 // Including this will define the __GLIBC__ macro if glibc is being 23 // used. 24 #include <climits> 25 26 #include "absl/base/config.h" 27 28 // Maybe one day we can rewrite this file not to require the elf 29 // symbol extensions in glibc, but for right now we need them. 30 #ifdef ABSL_HAVE_ELF_MEM_IMAGE 31 #error ABSL_HAVE_ELF_MEM_IMAGE cannot be directly set 32 #endif 33 34 #if defined(__ELF__) && !defined(__OpenBSD__) && !defined(__QNX__) && \ 35 !defined(__native_client__) && !defined(__asmjs__) && \ 36 !defined(__wasm__) && !defined(__HAIKU__) 37 #define ABSL_HAVE_ELF_MEM_IMAGE 1 38 #endif 39 40 #ifdef ABSL_HAVE_ELF_MEM_IMAGE 41 42 #include <link.h> // for ElfW 43 44 #if defined(__FreeBSD__) && !defined(ElfW) 45 #define ElfW(x) __ElfN(x) 46 #endif 47 48 namespace absl { 49 ABSL_NAMESPACE_BEGIN 50 namespace debugging_internal { 51 52 // An in-memory ELF image (may not exist on disk). 53 class ElfMemImage { 54 private: 55 // Sentinel: there could never be an elf image at &kInvalidBaseSentinel. 56 static const int kInvalidBaseSentinel; 57 58 public: 59 // Sentinel: there could never be an elf image at this address. 60 static constexpr const void *const kInvalidBase = 61 static_cast<const void*>(&kInvalidBaseSentinel); 62 63 // Information about a single vdso symbol. 64 // All pointers are into .dynsym, .dynstr, or .text of the VDSO. 65 // Do not free() them or modify through them. 66 struct SymbolInfo { 67 const char *name; // E.g. "__vdso_getcpu" 68 const char *version; // E.g. "LINUX_2.6", could be "" 69 // for unversioned symbol. 70 const void *address; // Relocated symbol address. 71 const ElfW(Sym) *symbol; // Symbol in the dynamic symbol table. 72 }; 73 74 // Supports iteration over all dynamic symbols. 75 class SymbolIterator { 76 public: 77 friend class ElfMemImage; 78 const SymbolInfo *operator->() const; 79 const SymbolInfo &operator*() const; 80 SymbolIterator& operator++(); 81 bool operator!=(const SymbolIterator &rhs) const; 82 bool operator==(const SymbolIterator &rhs) const; 83 private: 84 SymbolIterator(const void *const image, int index); 85 void Update(int incr); 86 SymbolInfo info_; 87 int index_; 88 const void *const image_; 89 }; 90 91 92 explicit ElfMemImage(const void *base); 93 void Init(const void *base); IsPresent()94 bool IsPresent() const { return ehdr_ != nullptr; } 95 const ElfW(Phdr)* GetPhdr(int index) const; 96 const ElfW(Sym)* GetDynsym(int index) const; 97 const ElfW(Versym)* GetVersym(int index) const; 98 const ElfW(Verdef)* GetVerdef(int index) const; 99 const ElfW(Verdaux)* GetVerdefAux(const ElfW(Verdef) *verdef) const; 100 const char* GetDynstr(ElfW(Word) offset) const; 101 const void* GetSymAddr(const ElfW(Sym) *sym) const; 102 const char* GetVerstr(ElfW(Word) offset) const; 103 int GetNumSymbols() const; 104 105 SymbolIterator begin() const; 106 SymbolIterator end() const; 107 108 // Look up versioned dynamic symbol in the image. 109 // Returns false if image is not present, or doesn't contain given 110 // symbol/version/type combination. 111 // If info_out is non-null, additional details are filled in. 112 bool LookupSymbol(const char *name, const char *version, 113 int symbol_type, SymbolInfo *info_out) const; 114 115 // Find info about symbol (if any) which overlaps given address. 116 // Returns true if symbol was found; false if image isn't present 117 // or doesn't have a symbol overlapping given address. 118 // If info_out is non-null, additional details are filled in. 119 bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const; 120 121 private: 122 const ElfW(Ehdr) *ehdr_; 123 const ElfW(Sym) *dynsym_; 124 const ElfW(Versym) *versym_; 125 const ElfW(Verdef) *verdef_; 126 const ElfW(Word) *hash_; 127 const char *dynstr_; 128 size_t strsize_; 129 size_t verdefnum_; 130 ElfW(Addr) link_base_; // Link-time base (p_vaddr of first PT_LOAD). 131 }; 132 133 } // namespace debugging_internal 134 ABSL_NAMESPACE_END 135 } // namespace absl 136 137 #endif // ABSL_HAVE_ELF_MEM_IMAGE 138 139 #endif // ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_ 140