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      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,
     52                            bool writable,
     53                            bool program_header_only,
     54                            bool low_4gb,
     55                            std::string* error_msg,
     56                            uint8_t* requested_base = nullptr);
     57   static ElfFileImpl* Open(File* file,
     58                            int mmap_prot,
     59                            int mmap_flags,
     60                            bool low_4gb,
     61                            std::string* error_msg);
     62   ~ElfFileImpl();
     63 
     64   const File& GetFile() const {
     65     return *file_;
     66   }
     67 
     68   uint8_t* Begin() const {
     69     return map_->Begin();
     70   }
     71 
     72   uint8_t* End() const {
     73     return map_->End();
     74   }
     75 
     76   size_t Size() const {
     77     return map_->Size();
     78   }
     79 
     80   Elf_Ehdr& GetHeader() const;
     81 
     82   Elf_Word GetProgramHeaderNum() const;
     83   Elf_Phdr* GetProgramHeader(Elf_Word) const;
     84 
     85   Elf_Word GetSectionHeaderNum() const;
     86   Elf_Shdr* GetSectionHeader(Elf_Word) const;
     87   Elf_Shdr* FindSectionByType(Elf_Word type) const;
     88   Elf_Shdr* FindSectionByName(const std::string& name) const;
     89 
     90   Elf_Shdr* GetSectionNameStringSection() const;
     91 
     92   // Find .dynsym using .hash for more efficient lookup than FindSymbolAddress.
     93   const uint8_t* FindDynamicSymbolAddress(const std::string& symbol_name) const;
     94 
     95   static bool IsSymbolSectionType(Elf_Word section_type);
     96   Elf_Word GetSymbolNum(Elf_Shdr&) const;
     97   Elf_Sym* GetSymbol(Elf_Word section_type, Elf_Word i) const;
     98 
     99   // Find address of symbol in specified table, returning 0 if it is
    100   // not found. See FindSymbolByName for an explanation of build_map.
    101   Elf_Addr FindSymbolAddress(Elf_Word section_type,
    102                              const std::string& symbol_name,
    103                              bool build_map);
    104 
    105   // Lookup a string given string section and offset. Returns null for special 0 offset.
    106   const char* GetString(Elf_Shdr&, Elf_Word) const;
    107 
    108   Elf_Word GetDynamicNum() const;
    109   Elf_Dyn& GetDynamic(Elf_Word) const;
    110 
    111   Elf_Word GetRelNum(Elf_Shdr&) const;
    112   Elf_Rel& GetRel(Elf_Shdr&, Elf_Word) const;
    113 
    114   Elf_Word GetRelaNum(Elf_Shdr&) const;
    115   Elf_Rela& GetRela(Elf_Shdr&, Elf_Word) const;
    116 
    117   // Retrieves the expected size when the file is loaded at runtime. Returns true if successful.
    118   bool GetLoadedSize(size_t* size, std::string* error_msg) const;
    119 
    120   // Load segments into memory based on PT_LOAD program headers.
    121   // executable is true at run time, false at compile time.
    122   bool Load(bool executable, bool low_4gb, std::string* error_msg);
    123 
    124   bool Fixup(Elf_Addr base_address);
    125   bool FixupDynamic(Elf_Addr base_address);
    126   bool FixupSectionHeaders(Elf_Addr base_address);
    127   bool FixupProgramHeaders(Elf_Addr base_address);
    128   bool FixupSymbols(Elf_Addr base_address, bool dynamic);
    129   bool FixupRelocations(Elf_Addr base_address);
    130   bool FixupDebugSections(Elf_Addr base_address_delta);
    131   bool ApplyOatPatchesTo(const char* target_section_name, Elf_Addr base_address_delta);
    132   static void ApplyOatPatches(const uint8_t* patches, const uint8_t* patches_end, Elf_Addr delta,
    133                               uint8_t* to_patch, const uint8_t* to_patch_end);
    134 
    135   bool Strip(std::string* error_msg);
    136 
    137  private:
    138   ElfFileImpl(File* file, bool writable, bool program_header_only, uint8_t* requested_base);
    139 
    140   bool Setup(int prot, int flags, bool low_4gb, std::string* error_msg);
    141 
    142   bool SetMap(MemMap* map, std::string* error_msg);
    143 
    144   uint8_t* GetProgramHeadersStart() const;
    145   uint8_t* GetSectionHeadersStart() const;
    146   Elf_Phdr& GetDynamicProgramHeader() const;
    147   Elf_Dyn* GetDynamicSectionStart() const;
    148   Elf_Sym* GetSymbolSectionStart(Elf_Word section_type) const;
    149   const char* GetStringSectionStart(Elf_Word section_type) const;
    150   Elf_Rel* GetRelSectionStart(Elf_Shdr&) const;
    151   Elf_Rela* GetRelaSectionStart(Elf_Shdr&) const;
    152   Elf_Word* GetHashSectionStart() const;
    153   Elf_Word GetHashBucketNum() const;
    154   Elf_Word GetHashChainNum() const;
    155   Elf_Word GetHashBucket(size_t i, bool* ok) const;
    156   Elf_Word GetHashChain(size_t i, bool* ok) const;
    157 
    158   typedef std::map<std::string, Elf_Sym*> SymbolTable;
    159   SymbolTable** GetSymbolTable(Elf_Word section_type);
    160 
    161   bool ValidPointer(const uint8_t* start) const;
    162 
    163   const Elf_Sym* FindDynamicSymbol(const std::string& symbol_name) const;
    164 
    165   // Check that certain sections and their dependencies exist.
    166   bool CheckSectionsExist(std::string* error_msg) const;
    167 
    168   // Check that the link of the first section links to the second section.
    169   bool CheckSectionsLinked(const uint8_t* source, const uint8_t* target) const;
    170 
    171   // Check whether the offset is in range, and set to target to Begin() + offset if OK.
    172   bool CheckAndSet(Elf32_Off offset, const char* label, uint8_t** target, std::string* error_msg);
    173 
    174   // Find symbol in specified table, returning null if it is not found.
    175   //
    176   // If build_map is true, builds a map to speed repeated access. The
    177   // map does not included untyped symbol values (aka STT_NOTYPE)
    178   // since they can contain duplicates. If build_map is false, the map
    179   // will be used if it was already created. Typically build_map
    180   // should be set unless only a small number of symbols will be
    181   // looked up.
    182   Elf_Sym* FindSymbolByName(Elf_Word section_type,
    183                             const std::string& symbol_name,
    184                             bool build_map);
    185 
    186   Elf_Phdr* FindProgamHeaderByType(Elf_Word type) const;
    187 
    188   Elf_Dyn* FindDynamicByType(Elf_Sword type) const;
    189   Elf_Word FindDynamicValueByType(Elf_Sword type) const;
    190 
    191   // Lookup a string by section type. Returns null for special 0 offset.
    192   const char* GetString(Elf_Word section_type, Elf_Word) const;
    193 
    194   const File* const file_;
    195   const bool writable_;
    196   const bool program_header_only_;
    197 
    198   // ELF header mapping. If program_header_only_ is false, will
    199   // actually point to the entire elf file.
    200   std::unique_ptr<MemMap> map_;
    201   Elf_Ehdr* header_;
    202   std::vector<MemMap*> segments_;
    203 
    204   // Pointer to start of first PT_LOAD program segment after Load()
    205   // when program_header_only_ is true.
    206   uint8_t* base_address_;
    207 
    208   // The program header should always available but use GetProgramHeadersStart() to be sure.
    209   uint8_t* program_headers_start_;
    210 
    211   // Conditionally available values. Use accessors to ensure they exist if they are required.
    212   uint8_t* section_headers_start_;
    213   Elf_Phdr* dynamic_program_header_;
    214   Elf_Dyn* dynamic_section_start_;
    215   Elf_Sym* symtab_section_start_;
    216   Elf_Sym* dynsym_section_start_;
    217   char* strtab_section_start_;
    218   char* dynstr_section_start_;
    219   Elf_Word* hash_section_start_;
    220 
    221   SymbolTable* symtab_symbol_table_;
    222   SymbolTable* dynsym_symbol_table_;
    223 
    224   // Override the 'base' p_vaddr in the first LOAD segment with this value (if non-null).
    225   uint8_t* requested_base_;
    226 
    227   DISALLOW_COPY_AND_ASSIGN(ElfFileImpl);
    228 };
    229 
    230 }  // namespace art
    231 
    232 #endif  // ART_RUNTIME_ELF_FILE_IMPL_H_
    233