elf_file.h revision 3470ab4011b5e18d590d5375e2f13a1e3bd69222 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
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 *      http://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#ifndef ART_RUNTIME_ELF_FILE_H_
18#define ART_RUNTIME_ELF_FILE_H_
19
20#include <map>
21#include <memory>
22#include <vector>
23
24#include "base/unix_file/fd_file.h"
25#include "globals.h"
26#include "elf_utils.h"
27#include "mem_map.h"
28#include "os.h"
29
30namespace art {
31
32// Interface to GDB JIT for backtrace information.
33extern "C" {
34  struct JITCodeEntry;
35}
36
37
38// Used for compile time and runtime for ElfFile access. Because of
39// the need for use at runtime, cannot directly use LLVM classes such as
40// ELFObjectFile.
41class ElfFile {
42 public:
43  static ElfFile* Open(File* file, bool writable, bool program_header_only, std::string* error_msg);
44  // Open with specific mmap flags, Always maps in the whole file, not just the
45  // program header sections.
46  static ElfFile* Open(File* file, int mmap_prot, int mmap_flags, std::string* error_msg);
47  ~ElfFile();
48
49  // Load segments into memory based on PT_LOAD program headers
50
51  const File& GetFile() const {
52    return *file_;
53  }
54
55  byte* Begin() const {
56    return map_->Begin();
57  }
58
59  byte* End() const {
60    return map_->End();
61  }
62
63  size_t Size() const {
64    return map_->Size();
65  }
66
67  Elf32_Ehdr& GetHeader() const;
68
69  Elf32_Word GetProgramHeaderNum() const;
70  Elf32_Phdr& GetProgramHeader(Elf32_Word) const;
71  Elf32_Phdr* FindProgamHeaderByType(Elf32_Word type) const;
72
73  Elf32_Word GetSectionHeaderNum() const;
74  Elf32_Shdr& GetSectionHeader(Elf32_Word) const;
75  Elf32_Shdr* FindSectionByType(Elf32_Word type) const;
76  Elf32_Shdr* FindSectionByName(const std::string& name) const;
77
78  Elf32_Shdr& GetSectionNameStringSection() const;
79
80  // Find .dynsym using .hash for more efficient lookup than FindSymbolAddress.
81  const byte* FindDynamicSymbolAddress(const std::string& symbol_name) const;
82  const Elf32_Sym* FindDynamicSymbol(const std::string& symbol_name) const;
83
84  static bool IsSymbolSectionType(Elf32_Word section_type);
85  Elf32_Word GetSymbolNum(Elf32_Shdr&) const;
86  Elf32_Sym& GetSymbol(Elf32_Word section_type, Elf32_Word i) const;
87
88  // Find symbol in specified table, returning nullptr if it is not found.
89  //
90  // If build_map is true, builds a map to speed repeated access. The
91  // map does not included untyped symbol values (aka STT_NOTYPE)
92  // since they can contain duplicates. If build_map is false, the map
93  // will be used if it was already created. Typically build_map
94  // should be set unless only a small number of symbols will be
95  // looked up.
96  Elf32_Sym* FindSymbolByName(Elf32_Word section_type,
97                              const std::string& symbol_name,
98                              bool build_map);
99
100  // Find address of symbol in specified table, returning 0 if it is
101  // not found. See FindSymbolByName for an explanation of build_map.
102  Elf32_Addr FindSymbolAddress(Elf32_Word section_type,
103                               const std::string& symbol_name,
104                               bool build_map);
105
106  // Lookup a string given string section and offset. Returns nullptr for
107  // special 0 offset.
108  const char* GetString(Elf32_Shdr&, Elf32_Word) const;
109
110  // Lookup a string by section type. Returns nullptr for special 0 offset.
111  const char* GetString(Elf32_Word section_type, Elf32_Word) const;
112
113  Elf32_Word GetDynamicNum() const;
114  Elf32_Dyn& GetDynamic(Elf32_Word) const;
115  Elf32_Word FindDynamicValueByType(Elf32_Sword type) const;
116
117  Elf32_Word GetRelNum(Elf32_Shdr&) const;
118  Elf32_Rel& GetRel(Elf32_Shdr&, Elf32_Word) const;
119
120  Elf32_Word GetRelaNum(Elf32_Shdr&) const;
121  Elf32_Rela& GetRela(Elf32_Shdr&, Elf32_Word) const;
122
123  // Returns the expected size when the file is loaded at runtime
124  size_t GetLoadedSize() const;
125
126  // Load segments into memory based on PT_LOAD program headers.
127  // executable is true at run time, false at compile time.
128  bool Load(bool executable, std::string* error_msg);
129
130 private:
131  ElfFile(File* file, bool writable, bool program_header_only);
132
133  bool Setup(int prot, int flags, std::string* error_msg);
134
135  bool SetMap(MemMap* map, std::string* error_msg);
136
137  byte* GetProgramHeadersStart() const;
138  byte* GetSectionHeadersStart() const;
139  Elf32_Phdr& GetDynamicProgramHeader() const;
140  Elf32_Dyn* GetDynamicSectionStart() const;
141  Elf32_Sym* GetSymbolSectionStart(Elf32_Word section_type) const;
142  const char* GetStringSectionStart(Elf32_Word section_type) const;
143  Elf32_Rel* GetRelSectionStart(Elf32_Shdr&) const;
144  Elf32_Rela* GetRelaSectionStart(Elf32_Shdr&) const;
145  Elf32_Word* GetHashSectionStart() const;
146  Elf32_Word GetHashBucketNum() const;
147  Elf32_Word GetHashChainNum() const;
148  Elf32_Word GetHashBucket(size_t i) const;
149  Elf32_Word GetHashChain(size_t i) const;
150
151  typedef std::map<std::string, Elf32_Sym*> SymbolTable;
152  SymbolTable** GetSymbolTable(Elf32_Word section_type);
153
154  bool ValidPointer(const byte* start) const;
155
156  const File* const file_;
157  const bool writable_;
158  const bool program_header_only_;
159
160  // ELF header mapping. If program_header_only_ is false, will
161  // actually point to the entire elf file.
162  std::unique_ptr<MemMap> map_;
163  Elf32_Ehdr* header_;
164  std::vector<MemMap*> segments_;
165
166  // Pointer to start of first PT_LOAD program segment after Load()
167  // when program_header_only_ is true.
168  byte* base_address_;
169
170  // The program header should always available but use GetProgramHeadersStart() to be sure.
171  byte* program_headers_start_;
172
173  // Conditionally available values. Use accessors to ensure they exist if they are required.
174  byte* section_headers_start_;
175  Elf32_Phdr* dynamic_program_header_;
176  Elf32_Dyn* dynamic_section_start_;
177  Elf32_Sym* symtab_section_start_;
178  Elf32_Sym* dynsym_section_start_;
179  char* strtab_section_start_;
180  char* dynstr_section_start_;
181  Elf32_Word* hash_section_start_;
182
183  SymbolTable* symtab_symbol_table_;
184  SymbolTable* dynsym_symbol_table_;
185
186  // Support for GDB JIT
187  byte* jit_elf_image_;
188  JITCodeEntry* jit_gdb_entry_;
189  std::unique_ptr<ElfFile> gdb_file_mapping_;
190  void GdbJITSupport();
191};
192
193}  // namespace art
194
195#endif  // ART_RUNTIME_ELF_FILE_H_
196