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      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>
     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