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(__GLIBC__) && !defined(__native_client__) && \ 35 !defined(__asmjs__) && !defined(__wasm__) 36 #define ABSL_HAVE_ELF_MEM_IMAGE 1 37 #endif 38 39 #ifdef ABSL_HAVE_ELF_MEM_IMAGE 40 41 #include <link.h> // for ElfW 42 43 namespace absl { 44 ABSL_NAMESPACE_BEGIN 45 namespace debugging_internal { 46 47 // An in-memory ELF image (may not exist on disk). 48 class ElfMemImage { 49 private: 50 // Sentinel: there could never be an elf image at &kInvalidBaseSentinel. 51 static const int kInvalidBaseSentinel; 52 53 public: 54 // Sentinel: there could never be an elf image at this address. 55 static constexpr const void *const kInvalidBase = 56 static_cast<const void*>(&kInvalidBaseSentinel); 57 58 // Information about a single vdso symbol. 59 // All pointers are into .dynsym, .dynstr, or .text of the VDSO. 60 // Do not free() them or modify through them. 61 struct SymbolInfo { 62 const char *name; // E.g. "__vdso_getcpu" 63 const char *version; // E.g. "LINUX_2.6", could be "" 64 // for unversioned symbol. 65 const void *address; // Relocated symbol address. 66 const ElfW(Sym) *symbol; // Symbol in the dynamic symbol table. 67 }; 68 69 // Supports iteration over all dynamic symbols. 70 class SymbolIterator { 71 public: 72 friend class ElfMemImage; 73 const SymbolInfo *operator->() const; 74 const SymbolInfo &operator*() const; 75 SymbolIterator& operator++(); 76 bool operator!=(const SymbolIterator &rhs) const; 77 bool operator==(const SymbolIterator &rhs) const; 78 private: 79 SymbolIterator(const void *const image, int index); 80 void Update(int incr); 81 SymbolInfo info_; 82 int index_; 83 const void *const image_; 84 }; 85 86 87 explicit ElfMemImage(const void *base); 88 void Init(const void *base); IsPresent()89 bool IsPresent() const { return ehdr_ != nullptr; } 90 const ElfW(Phdr)* GetPhdr(int index) const; 91 const ElfW(Sym)* GetDynsym(int index) const; 92 const ElfW(Versym)* GetVersym(int index) const; 93 const ElfW(Verdef)* GetVerdef(int index) const; 94 const ElfW(Verdaux)* GetVerdefAux(const ElfW(Verdef) *verdef) const; 95 const char* GetDynstr(ElfW(Word) offset) const; 96 const void* GetSymAddr(const ElfW(Sym) *sym) const; 97 const char* GetVerstr(ElfW(Word) offset) const; 98 int GetNumSymbols() const; 99 100 SymbolIterator begin() const; 101 SymbolIterator end() const; 102 103 // Look up versioned dynamic symbol in the image. 104 // Returns false if image is not present, or doesn't contain given 105 // symbol/version/type combination. 106 // If info_out is non-null, additional details are filled in. 107 bool LookupSymbol(const char *name, const char *version, 108 int symbol_type, SymbolInfo *info_out) const; 109 110 // Find info about symbol (if any) which overlaps given address. 111 // Returns true if symbol was found; false if image isn't present 112 // or doesn't have a symbol overlapping given address. 113 // If info_out is non-null, additional details are filled in. 114 bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const; 115 116 private: 117 const ElfW(Ehdr) *ehdr_; 118 const ElfW(Sym) *dynsym_; 119 const ElfW(Versym) *versym_; 120 const ElfW(Verdef) *verdef_; 121 const ElfW(Word) *hash_; 122 const char *dynstr_; 123 size_t strsize_; 124 size_t verdefnum_; 125 ElfW(Addr) link_base_; // Link-time base (p_vaddr of first PT_LOAD). 126 }; 127 128 } // namespace debugging_internal 129 ABSL_NAMESPACE_END 130 } // namespace absl 131 132 #endif // ABSL_HAVE_ELF_MEM_IMAGE 133 134 #endif // ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_ 135