lld/Common/DWARF.cpp

   1 //===- DWARF.cpp ----------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "lld/Common/DWARF.h"
  10 #include "lld/Common/ErrorHandler.h"
  11
  12 using namespace llvm;
  13
  14 namespace lld {
  15
  16 DWARFCache::DWARFCache(std::unique_ptr<llvm::DWARFContext> d)
  17     : dwarf(std::move(d)) {
  18   for (std::unique_ptr<DWARFUnit> &cu : dwarf->compile_units()) {
  19     auto report = [](Error err) {
  20       handleAllErrors(std::move(err),
  21                       [](ErrorInfoBase &info) { warn(info.message()); });
  22     };
  23     Expected<const DWARFDebugLine::LineTable *> expectedLT =
  24         dwarf->getLineTableForUnit(cu.get(), report);
  25     const DWARFDebugLine::LineTable *lt = nullptr;
  26     if (expectedLT)
  27       lt = *expectedLT;
  28     else
  29       report(expectedLT.takeError());
  30     if (!lt)
  31       continue;
  32     lineTables.push_back(lt);
  33
  34     // Loop over variable records and insert them to variableLoc.
  35     for (const auto &entry : cu->dies()) {
  36       DWARFDie die(cu.get(), &entry);
  37       // Skip all tags that are not variables.
  38       if (die.getTag() != dwarf::DW_TAG_variable)
  39         continue;
  40
  41       // Skip if a local variable because we don't need them for generating
  42       // error messages. In general, only non-local symbols can fail to be
  43       // linked.
  44       if (!dwarf::toUnsigned(die.find(dwarf::DW_AT_external), 0))
  45         continue;
  46
  47       // Get the source filename index for the variable.
  48       unsigned file = dwarf::toUnsigned(die.find(dwarf::DW_AT_decl_file), 0);
  49       if (!lt->hasFileAtIndex(file))
  50         continue;
  51
  52       // Get the line number on which the variable is declared.
  53       unsigned line = dwarf::toUnsigned(die.find(dwarf::DW_AT_decl_line), 0);
  54
  55       // Here we want to take the variable name to add it into variableLoc.
  56       // Variable can have regular and linkage name associated. At first, we try
  57       // to get linkage name as it can be different, for example when we have
  58       // two variables in different namespaces of the same object. Use common
  59       // name otherwise, but handle the case when it also absent in case if the
  60       // input object file lacks some debug info.
  61       StringRef name =
  62           dwarf::toString(die.find(dwarf::DW_AT_linkage_name),
  63                           dwarf::toString(die.find(dwarf::DW_AT_name), ""));
  64       if (!name.empty())
  65         variableLoc.insert({name, {lt, file, line}});
  66     }
  67   }
  68 }
  69
  70 // Returns the pair of file name and line number describing location of data
  71 // object (variable, array, etc) definition.
  72 Optional<std::pair<std::string, unsigned>>
  73 DWARFCache::getVariableLoc(StringRef name) {
  74   // Return if we have no debug information about data object.
  75   auto it = variableLoc.find(name);
  76   if (it == variableLoc.end())
  77     return None;
  78
  79   // Take file name string from line table.
  80   std::string fileName;
  81   if (!it->second.lt->getFileNameByIndex(
  82           it->second.file, {},
  83           DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, fileName))
  84     return None;
  85
  86   return std::make_pair(fileName, it->second.line);
  87 }
  88
  89 // Returns source line information for a given offset
  90 // using DWARF debug info.
  91 Optional<DILineInfo> DWARFCache::getDILineInfo(uint64_t offset,
  92                                                uint64_t sectionIndex) {
  93   DILineInfo info;
  94   for (const llvm::DWARFDebugLine::LineTable *lt : lineTables) {
  95     if (lt->getFileLineInfoForAddress(
  96             {offset, sectionIndex}, nullptr,
  97             DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, info))
  98       return info;
  99   }
 100   return None;
 101 }
 102
 103 } // namespace lld