1 /* 2 * Copyright (C) 2018 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_LIBELFFILE_ELF_ELF_DEBUG_READER_H_ 18 #define ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_ 19 20 #include "base/array_ref.h" 21 #include "dwarf/headers.h" 22 #include "elf/elf_utils.h" 23 #include "xz_utils.h" 24 25 #include <map> 26 #include <string_view> 27 28 namespace art { 29 30 // Trivial ELF file reader. 31 // 32 // It is the bare minimum needed to read mini-debug-info symbols for unwinding. 33 // We use it to merge JIT mini-debug-infos together or to prune them after GC. 34 template <typename ElfTypes> 35 class ElfDebugReader { 36 public: 37 // Note that the input buffer might be misaligned. 38 typedef typename ElfTypes::Ehdr ALIGNED(1) Elf_Ehdr; 39 typedef typename ElfTypes::Shdr ALIGNED(1) Elf_Shdr; 40 typedef typename ElfTypes::Sym ALIGNED(1) Elf_Sym; 41 typedef typename ElfTypes::Addr ALIGNED(1) Elf_Addr; 42 43 // Call Frame Information. 44 struct CFI { 45 uint32_t length; // Length excluding the size of this field. 46 int32_t cie_pointer; // Offset in the section or -1 for CIE. 47 dataCFI48 const uint8_t* data() const { return reinterpret_cast<const uint8_t*>(this); } sizeCFI49 size_t size() const { return sizeof(uint32_t) + length; } 50 } PACKED(1); 51 52 // Common Information Entry. 53 struct CIE : public CFI { 54 } PACKED(1); 55 56 // Frame Description Entry. 57 struct FDE : public CFI { 58 Elf_Addr sym_addr; 59 Elf_Addr sym_size; 60 } PACKED(1); 61 ElfDebugReader(ArrayRef<const uint8_t> file)62 explicit ElfDebugReader(ArrayRef<const uint8_t> file) : file_(file) { 63 header_ = Read<Elf_Ehdr>(/*offset=*/ 0); 64 CHECK_EQ(header_->e_ident[0], ELFMAG0); 65 CHECK_EQ(header_->e_ident[1], ELFMAG1); 66 CHECK_EQ(header_->e_ident[2], ELFMAG2); 67 CHECK_EQ(header_->e_ident[3], ELFMAG3); 68 CHECK_EQ(header_->e_ehsize, sizeof(Elf_Ehdr)); 69 CHECK_EQ(header_->e_shentsize, sizeof(Elf_Shdr)); 70 71 // Find all ELF sections. 72 sections_ = Read<Elf_Shdr>(header_->e_shoff, header_->e_shnum); 73 for (const Elf_Shdr& section : sections_) { 74 const char* name = Read<char>(sections_[header_->e_shstrndx].sh_offset + section.sh_name); 75 section_map_[std::string_view(name)] = §ion; 76 } 77 78 // Decompressed embedded debug symbols, if any. 79 const Elf_Shdr* gnu_debugdata = section_map_[".gnu_debugdata"]; 80 if (gnu_debugdata != nullptr) { 81 auto compressed = Read<uint8_t>(gnu_debugdata->sh_offset, gnu_debugdata->sh_size); 82 XzDecompress(compressed, &decompressed_gnu_debugdata_); 83 gnu_debugdata_reader_.reset(new ElfDebugReader(decompressed_gnu_debugdata_)); 84 } 85 } 86 ElfDebugReader(std::vector<uint8_t> & file)87 explicit ElfDebugReader(std::vector<uint8_t>& file) 88 : ElfDebugReader(ArrayRef<const uint8_t>(file)) { 89 } 90 GetHeader()91 const Elf_Ehdr* GetHeader() { return header_; } 92 GetSections()93 ArrayRef<Elf_Shdr> GetSections() { return sections_; } 94 GetSection(const char * name)95 const Elf_Shdr* GetSection(const char* name) { return section_map_[name]; } 96 97 template <typename VisitSym> VisitFunctionSymbols(VisitSym visit_sym)98 void VisitFunctionSymbols(VisitSym visit_sym) { 99 const Elf_Shdr* symtab = GetSection(".symtab"); 100 const Elf_Shdr* strtab = GetSection(".strtab"); 101 const Elf_Shdr* text = GetSection(".text"); 102 if (symtab != nullptr && strtab != nullptr) { 103 CHECK_EQ(symtab->sh_entsize, sizeof(Elf_Sym)); 104 size_t count = symtab->sh_size / sizeof(Elf_Sym); 105 for (const Elf_Sym& symbol : Read<Elf_Sym>(symtab->sh_offset, count)) { 106 if (ELF_ST_TYPE(symbol.st_info) == STT_FUNC && §ions_[symbol.st_shndx] == text) { 107 visit_sym(symbol, Read<char>(strtab->sh_offset + symbol.st_name)); 108 } 109 } 110 } 111 if (gnu_debugdata_reader_ != nullptr) { 112 gnu_debugdata_reader_->VisitFunctionSymbols(visit_sym); 113 } 114 } 115 116 template <typename VisitSym> VisitDynamicSymbols(VisitSym visit_sym)117 void VisitDynamicSymbols(VisitSym visit_sym) { 118 const Elf_Shdr* dynsym = GetSection(".dynsym"); 119 const Elf_Shdr* dynstr = GetSection(".dynstr"); 120 if (dynsym != nullptr && dynstr != nullptr) { 121 CHECK_EQ(dynsym->sh_entsize, sizeof(Elf_Sym)); 122 size_t count = dynsym->sh_size / sizeof(Elf_Sym); 123 for (const Elf_Sym& symbol : Read<Elf_Sym>(dynsym->sh_offset, count)) { 124 visit_sym(symbol, Read<char>(dynstr->sh_offset + symbol.st_name)); 125 } 126 } 127 } 128 129 template <typename VisitCIE, typename VisitFDE> VisitDebugFrame(VisitCIE visit_cie,VisitFDE visit_fde)130 void VisitDebugFrame(VisitCIE visit_cie, VisitFDE visit_fde) { 131 const Elf_Shdr* debug_frame = GetSection(".debug_frame"); 132 if (debug_frame != nullptr) { 133 for (size_t offset = 0; offset < debug_frame->sh_size;) { 134 const CFI* entry = Read<CFI>(debug_frame->sh_offset + offset); 135 DCHECK_LE(entry->size(), debug_frame->sh_size - offset); 136 if (entry->cie_pointer == -1) { 137 visit_cie(Read<CIE>(debug_frame->sh_offset + offset)); 138 } else { 139 const FDE* fde = Read<FDE>(debug_frame->sh_offset + offset); 140 visit_fde(fde, Read<CIE>(debug_frame->sh_offset + fde->cie_pointer)); 141 } 142 offset += entry->size(); 143 } 144 } 145 if (gnu_debugdata_reader_ != nullptr) { 146 gnu_debugdata_reader_->VisitDebugFrame(visit_cie, visit_fde); 147 } 148 } 149 150 private: 151 template<typename T> Read(size_t offset)152 const T* Read(size_t offset) { 153 DCHECK_LE(offset + sizeof(T), file_.size()); 154 return reinterpret_cast<const T*>(file_.data() + offset); 155 } 156 157 template<typename T> Read(size_t offset,size_t count)158 ArrayRef<const T> Read(size_t offset, size_t count) { 159 DCHECK_LE(offset + count * sizeof(T), file_.size()); 160 return ArrayRef<const T>(Read<T>(offset), count); 161 } 162 163 ArrayRef<const uint8_t> const file_; 164 const Elf_Ehdr* header_; 165 ArrayRef<const Elf_Shdr> sections_; 166 std::unordered_map<std::string_view, const Elf_Shdr*> section_map_; 167 std::vector<uint8_t> decompressed_gnu_debugdata_; 168 std::unique_ptr<ElfDebugReader> gnu_debugdata_reader_; 169 170 DISALLOW_COPY_AND_ASSIGN(ElfDebugReader); 171 }; 172 173 } // namespace art 174 #endif // ART_LIBELFFILE_ELF_ELF_DEBUG_READER_H_ 175