1 /*
2 * Copyright (C) 2016 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_COMPILER_DEBUG_ELF_SYMTAB_WRITER_H_
18 #define ART_COMPILER_DEBUG_ELF_SYMTAB_WRITER_H_
19
20 #include <map>
21 #include <unordered_set>
22
23 #include "base/utils.h"
24 #include "debug/debug_info.h"
25 #include "debug/method_debug_info.h"
26 #include "dex/dex_file-inl.h"
27 #include "dex/code_item_accessors.h"
28 #include "elf/elf_builder.h"
29
30 namespace art {
31 namespace debug {
32
33 // The ARM specification defines three special mapping symbols
34 // $a, $t and $d which mark ARM, Thumb and data ranges respectively.
35 // These symbols can be used by tools, for example, to pretty
36 // print instructions correctly. Objdump will use them if they
37 // exist, but it will still work well without them.
38 // However, these extra symbols take space, so let's just generate
39 // one symbol which marks the whole .text section as code.
40 // Note that ARM's Streamline requires it to match function symbol.
41 constexpr bool kGenerateArmMappingSymbol = true;
42
43 // Magic name for .symtab symbols which enumerate dex files used
44 // by this ELF file (currently mmapped inside the .dex section).
45 constexpr const char* kDexFileSymbolName = "$dexfile";
46
47 template <typename ElfTypes>
WriteDebugSymbols(ElfBuilder<ElfTypes> * builder,bool mini_debug_info,const DebugInfo & debug_info)48 static void WriteDebugSymbols(ElfBuilder<ElfTypes>* builder,
49 bool mini_debug_info,
50 const DebugInfo& debug_info) {
51 uint64_t mapping_symbol_address = std::numeric_limits<uint64_t>::max();
52 const auto* text = builder->GetText();
53 auto* strtab = builder->GetStrTab();
54 auto* symtab = builder->GetSymTab();
55
56 if (debug_info.Empty()) {
57 return;
58 }
59
60 // Find all addresses which contain deduped methods.
61 // The first instance of method is not marked deduped_, but the rest is.
62 std::unordered_set<uint64_t> deduped_addresses;
63 for (const MethodDebugInfo& info : debug_info.compiled_methods) {
64 if (info.deduped) {
65 deduped_addresses.insert(info.code_address);
66 }
67 if (kGenerateArmMappingSymbol && info.isa == InstructionSet::kThumb2) {
68 uint64_t address = info.code_address;
69 address += info.is_code_address_text_relative ? text->GetAddress() : 0;
70 mapping_symbol_address = std::min(mapping_symbol_address, address);
71 }
72 }
73
74 strtab->Start();
75 strtab->Write(""); // strtab should start with empty string.
76 // Generate ARM mapping symbols. ELF local symbols must be added first.
77 if (mapping_symbol_address != std::numeric_limits<uint64_t>::max()) {
78 symtab->Add(strtab->Write("$t"), text, mapping_symbol_address, 0, STB_LOCAL, STT_NOTYPE);
79 }
80 // Add symbols for compiled methods.
81 for (const MethodDebugInfo& info : debug_info.compiled_methods) {
82 if (info.deduped) {
83 continue; // Add symbol only for the first instance.
84 }
85 size_t name_offset;
86 if (!info.custom_name.empty()) {
87 name_offset = strtab->Write(info.custom_name);
88 } else {
89 DCHECK(info.dex_file != nullptr);
90 std::string name = info.dex_file->PrettyMethod(info.dex_method_index, !mini_debug_info);
91 if (deduped_addresses.find(info.code_address) != deduped_addresses.end()) {
92 name += " [DEDUPED]";
93 }
94 name_offset = strtab->Write(name);
95 }
96
97 uint64_t address = info.code_address;
98 address += info.is_code_address_text_relative ? text->GetAddress() : 0;
99 // Add in code delta, e.g., thumb bit 0 for Thumb2 code.
100 address += CompiledMethod::CodeDelta(info.isa);
101 symtab->Add(name_offset, text, address, info.code_size, STB_GLOBAL, STT_FUNC);
102 }
103 // Add symbols for dex files.
104 if (!debug_info.dex_files.empty() && builder->GetDex()->Exists()) {
105 auto dex = builder->GetDex();
106 for (auto it : debug_info.dex_files) {
107 uint64_t dex_address = dex->GetAddress() + it.first /* offset within the section */;
108 const DexFile* dex_file = it.second;
109 typename ElfTypes::Word dex_name = strtab->Write(kDexFileSymbolName);
110 symtab->Add(dex_name, dex, dex_address, dex_file->Size(), STB_GLOBAL, STT_FUNC);
111 }
112 }
113 strtab->End();
114
115 // Symbols are buffered and written after names (because they are smaller).
116 symtab->WriteCachedSection();
117 }
118
119 } // namespace debug
120 } // namespace art
121
122 #endif // ART_COMPILER_DEBUG_ELF_SYMTAB_WRITER_H_
123
124