Home | History | Annotate | Download | only in debug 
      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>
     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 = info.dex_file->PrettyMethod(info.dex_method_index, 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