elf_file.h revision afa6b8e93a0dc0de33c9d404945c7c5621e20b1a 
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
72  Elf32_Word GetSectionHeaderNum() const;
73  Elf32_Shdr* GetSectionHeader(Elf32_Word) const;
74  Elf32_Shdr* FindSectionByType(Elf32_Word type) const;
75  Elf32_Shdr* FindSectionByName(const std::string& name) const;
76
77  Elf32_Shdr* GetSectionNameStringSection() const;
78
79  // Find .dynsym using .hash for more efficient lookup than FindSymbolAddress.
80  const byte* FindDynamicSymbolAddress(const std::string& symbol_name) const;
81
82  Elf32_Word GetSymbolNum(Elf32_Shdr&) const;
83  Elf32_Sym* GetSymbol(Elf32_Word section_type, Elf32_Word i) const;
84
85  // Find address of symbol in specified table, returning 0 if it is
86  // not found. See FindSymbolByName for an explanation of build_map.
87  Elf32_Addr FindSymbolAddress(Elf32_Word section_type,
88                               const std::string& symbol_name,
89                               bool build_map);
90
91  // Lookup a string given string section and offset. Returns nullptr for
92  // special 0 offset.
93  const char* GetString(Elf32_Shdr&, Elf32_Word) const;
94
95  Elf32_Word GetDynamicNum() const;
96  Elf32_Dyn& GetDynamic(Elf32_Word) const;
97
98  Elf32_Word GetRelNum(Elf32_Shdr&) const;
99  Elf32_Rel& GetRel(Elf32_Shdr&, Elf32_Word) const;
100
101  Elf32_Word GetRelaNum(Elf32_Shdr&) const;
102  Elf32_Rela& GetRela(Elf32_Shdr&, Elf32_Word) const;
103
104  // Returns the expected size when the file is loaded at runtime
105  size_t GetLoadedSize() const;
106
107  // Load segments into memory based on PT_LOAD program headers.
108  // executable is true at run time, false at compile time.
109  bool Load(bool executable, std::string* error_msg);
110
111 private:
112  ElfFile(File* file, bool writable, bool program_header_only);
113
114  bool Setup(int prot, int flags, std::string* error_msg);
115
116  bool SetMap(MemMap* map, std::string* error_msg);
117
118  byte* GetProgramHeadersStart() const;
119  byte* GetSectionHeadersStart() const;
120  Elf32_Phdr& GetDynamicProgramHeader() const;
121  Elf32_Dyn* GetDynamicSectionStart() const;
122  Elf32_Sym* GetSymbolSectionStart(Elf32_Word section_type) const;
123  const char* GetStringSectionStart(Elf32_Word section_type) const;
124  Elf32_Rel* GetRelSectionStart(Elf32_Shdr&) const;
125  Elf32_Rela* GetRelaSectionStart(Elf32_Shdr&) const;
126  Elf32_Word* GetHashSectionStart() const;
127  Elf32_Word GetHashBucketNum() const;
128  Elf32_Word GetHashChainNum() const;
129  Elf32_Word GetHashBucket(size_t i, bool* ok) const;
130  Elf32_Word GetHashChain(size_t i, bool* ok) const;
131
132  typedef std::map<std::string, Elf32_Sym*> SymbolTable;
133  SymbolTable** GetSymbolTable(Elf32_Word section_type);
134
135  bool ValidPointer(const byte* start) const;
136
137  const Elf32_Sym* FindDynamicSymbol(const std::string& symbol_name) const;
138
139  // Check that certain sections and their dependencies exist.
140  bool CheckSectionsExist(std::string* error_msg) const;
141
142  // Check that the link of the first section links to the second section.
143  bool CheckSectionsLinked(const byte* source, const byte* target) const;
144
145  // Check whether the offset is in range, and set to target to Begin() + offset if OK.
146  bool CheckAndSet(Elf32_Off offset, const char* label, byte** target, std::string* error_msg);
147
148  // Find symbol in specified table, returning nullptr if it is not found.
149  //
150  // If build_map is true, builds a map to speed repeated access. The
151  // map does not included untyped symbol values (aka STT_NOTYPE)
152  // since they can contain duplicates. If build_map is false, the map
153  // will be used if it was already created. Typically build_map
154  // should be set unless only a small number of symbols will be
155  // looked up.
156  Elf32_Sym* FindSymbolByName(Elf32_Word section_type,
157                              const std::string& symbol_name,
158                              bool build_map);
159
160  Elf32_Phdr* FindProgamHeaderByType(Elf32_Word type) const;
161
162  Elf32_Dyn* FindDynamicByType(Elf32_Sword type) const;
163  Elf32_Word FindDynamicValueByType(Elf32_Sword type) const;
164
165  // Lookup a string by section type. Returns nullptr for special 0 offset.
166  const char* GetString(Elf32_Word section_type, Elf32_Word) const;
167
168  const File* const file_;
169  const bool writable_;
170  const bool program_header_only_;
171
172  // ELF header mapping. If program_header_only_ is false, will
173  // actually point to the entire elf file.
174  std::unique_ptr<MemMap> map_;
175  Elf32_Ehdr* header_;
176  std::vector<MemMap*> segments_;
177
178  // Pointer to start of first PT_LOAD program segment after Load()
179  // when program_header_only_ is true.
180  byte* base_address_;
181
182  // The program header should always available but use GetProgramHeadersStart() to be sure.
183  byte* program_headers_start_;
184
185  // Conditionally available values. Use accessors to ensure they exist if they are required.
186  byte* section_headers_start_;
187  Elf32_Phdr* dynamic_program_header_;
188  Elf32_Dyn* dynamic_section_start_;
189  Elf32_Sym* symtab_section_start_;
190  Elf32_Sym* dynsym_section_start_;
191  char* strtab_section_start_;
192  char* dynstr_section_start_;
193  Elf32_Word* hash_section_start_;
194
195  SymbolTable* symtab_symbol_table_;
196  SymbolTable* dynsym_symbol_table_;
197
198  // Support for GDB JIT
199  byte* jit_elf_image_;
200  JITCodeEntry* jit_gdb_entry_;
201  std::unique_ptr<ElfFile> gdb_file_mapping_;
202  void GdbJITSupport();
203};
204
205}  // namespace art
206
207#endif  // ART_RUNTIME_ELF_FILE_H_
208