DWARF.cpp revision 360784 
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// The -gdb-index option instructs the linker to emit a .gdb_index section.
10// The section contains information to make gdb startup faster.
11// The format of the section is described at
12// https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html.
13//
14//===----------------------------------------------------------------------===//
15
16#include "DWARF.h"
17#include "Symbols.h"
18#include "Target.h"
19#include "lld/Common/Memory.h"
20#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
21#include "llvm/Object/ELFObjectFile.h"
22
23using namespace llvm;
24using namespace llvm::object;
25
26namespace lld {
27namespace elf {
28template <class ELFT> LLDDwarfObj<ELFT>::LLDDwarfObj(ObjFile<ELFT> *obj) {
29  for (InputSectionBase *sec : obj->getSections()) {
30    if (!sec)
31      continue;
32
33    if (LLDDWARFSection *m =
34            StringSwitch<LLDDWARFSection *>(sec->name)
35                .Case(".debug_addr", &addrSection)
36                .Case(".debug_gnu_pubnames", &gnuPubnamesSection)
37                .Case(".debug_gnu_pubtypes", &gnuPubtypesSection)
38                .Case(".debug_info", &infoSection)
39                .Case(".debug_ranges", &rangesSection)
40                .Case(".debug_rnglists", &rnglistsSection)
41                .Case(".debug_str_offsets", &strOffsetsSection)
42                .Case(".debug_line", &lineSection)
43                .Default(nullptr)) {
44      m->Data = toStringRef(sec->data());
45      m->sec = sec;
46      continue;
47    }
48
49    if (sec->name == ".debug_abbrev")
50      abbrevSection = toStringRef(sec->data());
51    else if (sec->name == ".debug_str")
52      strSection = toStringRef(sec->data());
53    else if (sec->name == ".debug_line_str")
54      lineStrSection = toStringRef(sec->data());
55  }
56}
57
58namespace {
59template <class RelTy> struct LLDRelocationResolver {
60  // In the ELF ABIs, S sepresents the value of the symbol in the relocation
61  // entry. For Rela, the addend is stored as part of the relocation entry.
62  static uint64_t resolve(object::RelocationRef ref, uint64_t s,
63                          uint64_t /* A */) {
64    return s + ref.getRawDataRefImpl().p;
65  }
66};
67
68template <class ELFT> struct LLDRelocationResolver<Elf_Rel_Impl<ELFT, false>> {
69  // For Rel, the addend A is supplied by the caller.
70  static uint64_t resolve(object::RelocationRef /*Ref*/, uint64_t s,
71                          uint64_t a) {
72    return s + a;
73  }
74};
75} // namespace
76
77// Find if there is a relocation at Pos in Sec.  The code is a bit
78// more complicated than usual because we need to pass a section index
79// to llvm since it has no idea about InputSection.
80template <class ELFT>
81template <class RelTy>
82Optional<RelocAddrEntry>
83LLDDwarfObj<ELFT>::findAux(const InputSectionBase &sec, uint64_t pos,
84                           ArrayRef<RelTy> rels) const {
85  auto it =
86      partition_point(rels, [=](const RelTy &a) { return a.r_offset < pos; });
87  if (it == rels.end() || it->r_offset != pos)
88    return None;
89  const RelTy &rel = *it;
90
91  const ObjFile<ELFT> *file = sec.getFile<ELFT>();
92  uint32_t symIndex = rel.getSymbol(config->isMips64EL);
93  const typename ELFT::Sym &sym = file->template getELFSyms<ELFT>()[symIndex];
94  uint32_t secIndex = file->getSectionIndex(sym);
95
96  // An undefined symbol may be a symbol defined in a discarded section. We
97  // shall still resolve it. This is important for --gdb-index: the end address
98  // offset of an entry in .debug_ranges is relocated. If it is not resolved,
99  // its zero value will terminate the decoding of .debug_ranges prematurely.
100  Symbol &s = file->getRelocTargetSym(rel);
101  uint64_t val = 0;
102  if (auto *dr = dyn_cast<Defined>(&s)) {
103    val = dr->value;
104
105    // FIXME: We should be consistent about always adding the file
106    // offset or not.
107    if (dr->section->flags & ELF::SHF_ALLOC)
108      val += cast<InputSection>(dr->section)->getOffsetInFile();
109  }
110
111  DataRefImpl d;
112  d.p = getAddend<ELFT>(rel);
113  return RelocAddrEntry{secIndex, RelocationRef(d, nullptr),
114                        val,      Optional<object::RelocationRef>(),
115                        0,        LLDRelocationResolver<RelTy>::resolve};
116}
117
118template <class ELFT>
119Optional<RelocAddrEntry> LLDDwarfObj<ELFT>::find(const llvm::DWARFSection &s,
120                                                 uint64_t pos) const {
121  auto &sec = static_cast<const LLDDWARFSection &>(s);
122  if (sec.sec->areRelocsRela)
123    return findAux(*sec.sec, pos, sec.sec->template relas<ELFT>());
124  return findAux(*sec.sec, pos, sec.sec->template rels<ELFT>());
125}
126
127template class LLDDwarfObj<ELF32LE>;
128template class LLDDwarfObj<ELF32BE>;
129template class LLDDwarfObj<ELF64LE>;
130template class LLDDwarfObj<ELF64BE>;
131
132} // namespace elf
133} // namespace lld
134