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
26namespace art {
27namespace 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.
36constexpr bool kGenerateSingleArmMappingSymbol = true;
37
38template <typename ElfTypes>
39static 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