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_IMPL_H_
18 #define ART_RUNTIME_ELF_FILE_IMPL_H_
19 
20 #include <map>
21 #include <memory>
22 #include <type_traits>
23 #include <vector>
24 
25 // Explicitly include our own elf.h to avoid Linux and other dependencies.
26 #include "./elf.h"
27 #include "mem_map.h"
28 
29 namespace art {
30 
31 extern "C" {
32   struct JITCodeEntry;
33 }
34 
35 template <typename ElfTypes>
36 class ElfFileImpl {
37  public:
38   using Elf_Addr = typename ElfTypes::Addr;
39   using Elf_Off = typename ElfTypes::Off;
40   using Elf_Half = typename ElfTypes::Half;
41   using Elf_Word = typename ElfTypes::Word;
42   using Elf_Sword = typename ElfTypes::Sword;
43   using Elf_Ehdr = typename ElfTypes::Ehdr;
44   using Elf_Shdr = typename ElfTypes::Shdr;
45   using Elf_Sym = typename ElfTypes::Sym;
46   using Elf_Rel = typename ElfTypes::Rel;
47   using Elf_Rela = typename ElfTypes::Rela;
48   using Elf_Phdr = typename ElfTypes::Phdr;
49   using Elf_Dyn = typename ElfTypes::Dyn;
50 
51   static ElfFileImpl* Open(File* file, bool writable, bool program_header_only,
52                            std::string* error_msg, uint8_t* requested_base = nullptr);
53   static ElfFileImpl* Open(File* file, int mmap_prot, int mmap_flags, std::string* error_msg);
54   ~ElfFileImpl();
55 
GetFile()56   const File& GetFile() const {
57     return *file_;
58   }
59 
Begin()60   uint8_t* Begin() const {
61     return map_->Begin();
62   }
63 
End()64   uint8_t* End() const {
65     return map_->End();
66   }
67 
Size()68   size_t Size() const {
69     return map_->Size();
70   }
71 
72   Elf_Ehdr& GetHeader() const;
73 
74   Elf_Word GetProgramHeaderNum() const;
75   Elf_Phdr* GetProgramHeader(Elf_Word) const;
76 
77   Elf_Word GetSectionHeaderNum() const;
78   Elf_Shdr* GetSectionHeader(Elf_Word) const;
79   Elf_Shdr* FindSectionByType(Elf_Word type) const;
80   Elf_Shdr* FindSectionByName(const std::string& name) const;
81 
82   Elf_Shdr* GetSectionNameStringSection() const;
83 
84   // Find .dynsym using .hash for more efficient lookup than FindSymbolAddress.
85   const uint8_t* FindDynamicSymbolAddress(const std::string& symbol_name) const;
86 
87   static bool IsSymbolSectionType(Elf_Word section_type);
88   Elf_Word GetSymbolNum(Elf_Shdr&) const;
89   Elf_Sym* GetSymbol(Elf_Word section_type, Elf_Word i) const;
90 
91   // Find address of symbol in specified table, returning 0 if it is
92   // not found. See FindSymbolByName for an explanation of build_map.
93   Elf_Addr FindSymbolAddress(Elf_Word section_type,
94                              const std::string& symbol_name,
95                              bool build_map);
96 
97   // Lookup a string given string section and offset. Returns null for special 0 offset.
98   const char* GetString(Elf_Shdr&, Elf_Word) const;
99 
100   Elf_Word GetDynamicNum() const;
101   Elf_Dyn& GetDynamic(Elf_Word) const;
102 
103   Elf_Word GetRelNum(Elf_Shdr&) const;
104   Elf_Rel& GetRel(Elf_Shdr&, Elf_Word) const;
105 
106   Elf_Word GetRelaNum(Elf_Shdr&) const;
107   Elf_Rela& GetRela(Elf_Shdr&, Elf_Word) const;
108 
109   // Retrieves the expected size when the file is loaded at runtime. Returns true if successful.
110   bool GetLoadedSize(size_t* size, std::string* error_msg) const;
111 
112   // Load segments into memory based on PT_LOAD program headers.
113   // executable is true at run time, false at compile time.
114   bool Load(bool executable, std::string* error_msg);
115 
116   bool Fixup(Elf_Addr base_address);
117   bool FixupDynamic(Elf_Addr base_address);
118   bool FixupSectionHeaders(Elf_Addr base_address);
119   bool FixupProgramHeaders(Elf_Addr base_address);
120   bool FixupSymbols(Elf_Addr base_address, bool dynamic);
121   bool FixupRelocations(Elf_Addr base_address);
122   bool FixupDebugSections(Elf_Addr base_address_delta);
123   bool ApplyOatPatchesTo(const char* target_section_name, Elf_Addr base_address_delta);
124   static void ApplyOatPatches(const uint8_t* patches, const uint8_t* patches_end, Elf_Addr delta,
125                               uint8_t* to_patch, const uint8_t* to_patch_end);
126 
127   bool Strip(std::string* error_msg);
128 
129  private:
130   ElfFileImpl(File* file, bool writable, bool program_header_only, uint8_t* requested_base);
131 
132   bool Setup(int prot, int flags, std::string* error_msg);
133 
134   bool SetMap(MemMap* map, std::string* error_msg);
135 
136   uint8_t* GetProgramHeadersStart() const;
137   uint8_t* GetSectionHeadersStart() const;
138   Elf_Phdr& GetDynamicProgramHeader() const;
139   Elf_Dyn* GetDynamicSectionStart() const;
140   Elf_Sym* GetSymbolSectionStart(Elf_Word section_type) const;
141   const char* GetStringSectionStart(Elf_Word section_type) const;
142   Elf_Rel* GetRelSectionStart(Elf_Shdr&) const;
143   Elf_Rela* GetRelaSectionStart(Elf_Shdr&) const;
144   Elf_Word* GetHashSectionStart() const;
145   Elf_Word GetHashBucketNum() const;
146   Elf_Word GetHashChainNum() const;
147   Elf_Word GetHashBucket(size_t i, bool* ok) const;
148   Elf_Word GetHashChain(size_t i, bool* ok) const;
149 
150   typedef std::map<std::string, Elf_Sym*> SymbolTable;
151   SymbolTable** GetSymbolTable(Elf_Word section_type);
152 
153   bool ValidPointer(const uint8_t* start) const;
154 
155   const Elf_Sym* FindDynamicSymbol(const std::string& symbol_name) const;
156 
157   // Check that certain sections and their dependencies exist.
158   bool CheckSectionsExist(std::string* error_msg) const;
159 
160   // Check that the link of the first section links to the second section.
161   bool CheckSectionsLinked(const uint8_t* source, const uint8_t* target) const;
162 
163   // Check whether the offset is in range, and set to target to Begin() + offset if OK.
164   bool CheckAndSet(Elf32_Off offset, const char* label, uint8_t** target, std::string* error_msg);
165 
166   // Find symbol in specified table, returning null if it is not found.
167   //
168   // If build_map is true, builds a map to speed repeated access. The
169   // map does not included untyped symbol values (aka STT_NOTYPE)
170   // since they can contain duplicates. If build_map is false, the map
171   // will be used if it was already created. Typically build_map
172   // should be set unless only a small number of symbols will be
173   // looked up.
174   Elf_Sym* FindSymbolByName(Elf_Word section_type,
175                             const std::string& symbol_name,
176                             bool build_map);
177 
178   Elf_Phdr* FindProgamHeaderByType(Elf_Word type) const;
179 
180   Elf_Dyn* FindDynamicByType(Elf_Sword type) const;
181   Elf_Word FindDynamicValueByType(Elf_Sword type) const;
182 
183   // Lookup a string by section type. Returns null for special 0 offset.
184   const char* GetString(Elf_Word section_type, Elf_Word) const;
185 
186   const File* const file_;
187   const bool writable_;
188   const bool program_header_only_;
189 
190   // ELF header mapping. If program_header_only_ is false, will
191   // actually point to the entire elf file.
192   std::unique_ptr<MemMap> map_;
193   Elf_Ehdr* header_;
194   std::vector<MemMap*> segments_;
195 
196   // Pointer to start of first PT_LOAD program segment after Load()
197   // when program_header_only_ is true.
198   uint8_t* base_address_;
199 
200   // The program header should always available but use GetProgramHeadersStart() to be sure.
201   uint8_t* program_headers_start_;
202 
203   // Conditionally available values. Use accessors to ensure they exist if they are required.
204   uint8_t* section_headers_start_;
205   Elf_Phdr* dynamic_program_header_;
206   Elf_Dyn* dynamic_section_start_;
207   Elf_Sym* symtab_section_start_;
208   Elf_Sym* dynsym_section_start_;
209   char* strtab_section_start_;
210   char* dynstr_section_start_;
211   Elf_Word* hash_section_start_;
212 
213   SymbolTable* symtab_symbol_table_;
214   SymbolTable* dynsym_symbol_table_;
215 
216   // Support for GDB JIT
217   uint8_t* jit_elf_image_;
218   JITCodeEntry* jit_gdb_entry_;
219   std::unique_ptr<ElfFileImpl<ElfTypes>> gdb_file_mapping_;
220   void GdbJITSupport();
221 
222   // Override the 'base' p_vaddr in the first LOAD segment with this value (if non-null).
223   uint8_t* requested_base_;
224 
225   DISALLOW_COPY_AND_ASSIGN(ElfFileImpl);
226 };
227 
228 }  // namespace art
229 
230 #endif  // ART_RUNTIME_ELF_FILE_IMPL_H_
231