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 <unordered_set>
21
22 #include "debug/method_debug_info.h"
23 #include "elf_builder.h"
24 #include "utils.h"
25
26 namespace art {
27 namespace debug {
28
29 // The ARM specification defines three special mapping symbols
30 // $a, $t and $d which mark ARM, Thumb and data ranges respectively.
31 // These symbols can be used by tools, for example, to pretty
32 // print instructions correctly. Objdump will use them if they
33 // exist, but it will still work well without them.
34 // However, these extra symbols take space, so let's just generate
35 // one symbol which marks the whole .text section as code.
36 constexpr bool kGenerateSingleArmMappingSymbol = true;
37
38 template <typename ElfTypes>
WriteDebugSymbols(ElfBuilder<ElfTypes> * builder,const ArrayRef<const MethodDebugInfo> & method_infos,bool with_signature)39 static void WriteDebugSymbols(ElfBuilder<ElfTypes>* builder,
40 const ArrayRef<const MethodDebugInfo>& method_infos,
41 bool with_signature) {
42 uint64_t mapping_symbol_address = std::numeric_limits<uint64_t>::max();
43 auto* strtab = builder->GetStrTab();
44 auto* symtab = builder->GetSymTab();
45
46 if (method_infos.empty()) {
47 return;
48 }
49
50 // Find all addresses which contain deduped methods.
51 // The first instance of method is not marked deduped_, but the rest is.
52 std::unordered_set<uint64_t> deduped_addresses;
53 for (const MethodDebugInfo& info : method_infos) {
54 if (info.deduped) {
55 deduped_addresses.insert(info.code_address);
56 }
57 }
58
59 strtab->Start();
60 strtab->Write(""); // strtab should start with empty string.
61 std::string last_name;
62 size_t last_name_offset = 0;
63 for (const MethodDebugInfo& info : method_infos) {
64 if (info.deduped) {
65 continue; // Add symbol only for the first instance.
66 }
67 size_t name_offset;
68 if (info.trampoline_name != nullptr) {
69 name_offset = strtab->Write(info.trampoline_name);
70 } else {
71 DCHECK(info.dex_file != nullptr);
72 std::string name = PrettyMethod(info.dex_method_index, *info.dex_file, with_signature);
73 if (deduped_addresses.find(info.code_address) != deduped_addresses.end()) {
74 name += " [DEDUPED]";
75 }
76 // If we write method names without signature, we might see the same name multiple times.
77 name_offset = (name == last_name ? last_name_offset : strtab->Write(name));
78 last_name = std::move(name);
79 last_name_offset = name_offset;
80 }
81
82 const auto* text = info.is_code_address_text_relative ? builder->GetText() : nullptr;
83 uint64_t address = info.code_address + (text != nullptr ? text->GetAddress() : 0);
84 // Add in code delta, e.g., thumb bit 0 for Thumb2 code.
85 address += CompiledMethod::CodeDelta(info.isa);
86 symtab->Add(name_offset, text, address, info.code_size, STB_GLOBAL, STT_FUNC);
87
88 // Conforming to aaelf, add $t mapping symbol to indicate start of a sequence of thumb2
89 // instructions, so that disassembler tools can correctly disassemble.
90 // Note that even if we generate just a single mapping symbol, ARM's Streamline
91 // requires it to match function symbol. Just address 0 does not work.
92 if (info.isa == kThumb2) {
93 if (address < mapping_symbol_address || !kGenerateSingleArmMappingSymbol) {
94 symtab->Add(strtab->Write("$t"), text, address & ~1, 0, STB_LOCAL, STT_NOTYPE);
95 mapping_symbol_address = address;
96 }
97 }
98 }
99 strtab->End();
100
101 // Symbols are buffered and written after names (because they are smaller).
102 // We could also do two passes in this function to avoid the buffering.
103 symtab->Start();
104 symtab->Write();
105 symtab->End();
106 }
107
108 } // namespace debug
109 } // namespace art
110
111 #endif // ART_COMPILER_DEBUG_ELF_SYMTAB_WRITER_H_
112
113