1// -*- mode: c++ -*-
2
3// Copyright (c) 2011 Google Inc. All Rights Reserved.
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30
31// Original author: Ted Mielczarek <ted.mielczarek@gmail.com>
32
33#include "common/linux/elf_symbols_to_module.h"
34
35#include <cxxabi.h>
36#include <elf.h>
37#include <string.h>
38
39#include "common/byte_cursor.h"
40#include "common/module.h"
41
42namespace google_breakpad {
43
44class ELFSymbolIterator {
45public:
46 // The contents of an ELF symbol, adjusted for the host's endianness,
47 // word size, and so on. Corresponds to the data in Elf32_Sym / Elf64_Sym.
48 struct Symbol {
49 // True if this iterator has reached the end of the symbol array. When
50 // this is set, the other members of this structure are not valid.
51 bool at_end;
52
53 // The number of this symbol within the list.
54 size_t index;
55
56 // The current symbol's name offset. This is the offset within the
57 // string table.
58 size_t name_offset;
59
60 // The current symbol's value, size, info and shndx fields.
61 uint64_t value;
62 uint64_t size;
63 unsigned char info;
64 uint16_t shndx;
65 };
66
67 // Create an ELFSymbolIterator walking the symbols in BUFFER. Treat the
68 // symbols as big-endian if BIG_ENDIAN is true, as little-endian
69 // otherwise. Assume each symbol has a 'value' field whose size is
70 // VALUE_SIZE.
71 //
72 ELFSymbolIterator(const ByteBuffer* buffer, bool big_endian,
73 size_t value_size)
74 : value_size_(value_size), cursor_(buffer, big_endian) {
75 // Actually, weird sizes could be handled just fine, but they're
76 // probably mistakes --- expressed in bits, say.
77 assert(value_size == 4 || value_size == 8);
78 symbol_.index = 0;
79 Fetch();
80 }
81
82 // Move to the next symbol. This function's behavior is undefined if
83 // at_end() is true when it is called.
84 ELFSymbolIterator& operator++() { Fetch(); symbol_.index++; return *this; }
85
86 // Dereferencing this iterator produces a reference to an Symbol structure
87 // that holds the current symbol's values. The symbol is owned by this
88 // SymbolIterator, and will be invalidated at the next call to operator++.
89 const Symbol& operator*() const { return symbol_; }
90 const Symbol* operator->() const { return &symbol_; }
91
92private:
93 // Read the symbol at cursor_, and set symbol_ appropriately.
94 void Fetch() {
95 // Elf32_Sym and Elf64_Sym have different layouts.
96 unsigned char other;
97 if (value_size_ == 4) {
98 // Elf32_Sym
99 cursor_
100 .Read(4, false, &symbol_.name_offset)
101 .Read(4, false, &symbol_.value)
102 .Read(4, false, &symbol_.size)
103 .Read(1, false, &symbol_.info)
104 .Read(1, false, &other)
105 .Read(2, false, &symbol_.shndx);
106 } else {
107 // Elf64_Sym
108 cursor_
109 .Read(4, false, &symbol_.name_offset)
110 .Read(1, false, &symbol_.info)
111 .Read(1, false, &other)
112 .Read(2, false, &symbol_.shndx)
113 .Read(8, false, &symbol_.value)
114 .Read(8, false, &symbol_.size);
115 }
116 symbol_.at_end = !cursor_;
117 }
118
119 // The size of symbols' value field, in bytes.
120 size_t value_size_;
121
122 // A byte cursor traversing buffer_.
123 ByteCursor cursor_;
124
125 // Values for the symbol this iterator refers to.
126 Symbol symbol_;
127};
128
129const char* SymbolString(ptrdiff_t offset, ByteBuffer& strings) {
130 if (offset < 0 || (size_t) offset >= strings.Size()) {
131 // Return the null string.
132 offset = 0;
133 }
134 return reinterpret_cast<const char*>(strings.start + offset);
135}
136
137bool ELFSymbolsToModule(const uint8_t* symtab_section,
138 size_t symtab_size,
139 const uint8_t* string_section,
140 size_t string_size,
141 const bool big_endian,
142 size_t value_size,
143 Module* module) {
144 ByteBuffer symbols(symtab_section, symtab_size);
145 // Ensure that the string section is null-terminated.
146 if (string_section[string_size - 1] != '\0') {
147 const void* null_terminator = memrchr(string_section, '\0', string_size);
148 string_size = reinterpret_cast<const uint8_t*>(null_terminator)
149 - string_section;
150 }
151 ByteBuffer strings(string_section, string_size);
152
153 // The iterator walking the symbol table.
154 ELFSymbolIterator iterator(&symbols, big_endian, value_size);
155
156 while(!iterator->at_end) {
157 if (ELF32_ST_TYPE(iterator->info) == STT_FUNC &&
158 iterator->shndx != SHN_UNDEF) {
159 Module::Extern* ext = new Module::Extern(iterator->value);
160 ext->name = SymbolString(iterator->name_offset, strings);
161#if !defined(__ANDROID__) // Android NDK doesn't provide abi::__cxa_demangle.
162 int status = 0;
163 char* demangled =
164 abi::__cxa_demangle(ext->name.c_str(), NULL, NULL, &status);
165 if (demangled) {
166 if (status == 0)
167 ext->name = demangled;
168 free(demangled);
169 }
170#endif
171 module->AddExtern(ext);
172 }
173 ++iterator;
174 }
175 return true;
176}
177
178} // namespace google_breakpad
179