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
12using namespace llvm;
13
14namespace lld {
15
16DWARFCache::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.
72std::optional<std::pair<std::string, unsigned>>
73DWARFCache::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 std::nullopt;
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 std::nullopt;
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.
91std::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 std::nullopt;
101}
102
103} // namespace lld
104