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;
25using namespace lld;
26using namespace lld::elf;
27
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", &rangeSection)
40                .Case(".debug_rnglists", &rngListsSection)
41                .Case(".debug_line", &lineSection)
42                .Default(nullptr)) {
43      m->Data = toStringRef(sec->data());
44      m->sec = sec;
45      continue;
46    }
47
48    if (sec->name == ".debug_abbrev")
49      abbrevSection = toStringRef(sec->data());
50    else if (sec->name == ".debug_str")
51      strSection = toStringRef(sec->data());
52    else if (sec->name == ".debug_line_str")
53      lineStringSection = toStringRef(sec->data());
54  }
55}
56
57namespace {
58template <class RelTy> struct LLDRelocationResolver {
59  // In the ELF ABIs, S sepresents the value of the symbol in the relocation
60  // entry. For Rela, the addend is stored as part of the relocation entry.
61  static uint64_t resolve(object::RelocationRef ref, uint64_t s,
62                          uint64_t /* A */) {
63    return s + ref.getRawDataRefImpl().p;
64  }
65};
66
67template <class ELFT> struct LLDRelocationResolver<Elf_Rel_Impl<ELFT, false>> {
68  // For Rel, the addend A is supplied by the caller.
69  static uint64_t resolve(object::RelocationRef /*Ref*/, uint64_t s,
70                          uint64_t a) {
71    return s + a;
72  }
73};
74} // namespace
75
76// Find if there is a relocation at Pos in Sec.  The code is a bit
77// more complicated than usual because we need to pass a section index
78// to llvm since it has no idea about InputSection.
79template <class ELFT>
80template <class RelTy>
81Optional<RelocAddrEntry>
82LLDDwarfObj<ELFT>::findAux(const InputSectionBase &sec, uint64_t pos,
83                           ArrayRef<RelTy> rels) const {
84  auto it =
85      partition_point(rels, [=](const RelTy &a) { return a.r_offset < pos; });
86  if (it == rels.end() || it->r_offset != pos)
87    return None;
88  const RelTy &rel = *it;
89
90  const ObjFile<ELFT> *file = sec.getFile<ELFT>();
91  uint32_t symIndex = rel.getSymbol(config->isMips64EL);
92  const typename ELFT::Sym &sym = file->template getELFSyms<ELFT>()[symIndex];
93  uint32_t secIndex = file->getSectionIndex(sym);
94
95  // An undefined symbol may be a symbol defined in a discarded section. We
96  // shall still resolve it. This is important for --gdb-index: the end address
97  // offset of an entry in .debug_ranges is relocated. If it is not resolved,
98  // its zero value will terminate the decoding of .debug_ranges prematurely.
99  Symbol &s = file->getRelocTargetSym(rel);
100  uint64_t val = 0;
101  if (auto *dr = dyn_cast<Defined>(&s)) {
102    val = dr->value;
103
104    // FIXME: We should be consistent about always adding the file
105    // offset or not.
106    if (dr->section->flags & ELF::SHF_ALLOC)
107      val += cast<InputSection>(dr->section)->getOffsetInFile();
108  }
109
110  DataRefImpl d;
111  d.p = getAddend<ELFT>(rel);
112  return RelocAddrEntry{secIndex, RelocationRef(d, nullptr),
113                        val,      Optional<object::RelocationRef>(),
114                        0,        LLDRelocationResolver<RelTy>::resolve};
115}
116
117template <class ELFT>
118Optional<RelocAddrEntry> LLDDwarfObj<ELFT>::find(const llvm::DWARFSection &s,
119                                                 uint64_t pos) const {
120  auto &sec = static_cast<const LLDDWARFSection &>(s);
121  if (sec.sec->areRelocsRela)
122    return findAux(*sec.sec, pos, sec.sec->template relas<ELFT>());
123  return findAux(*sec.sec, pos, sec.sec->template rels<ELFT>());
124}
125
126template class elf::LLDDwarfObj<ELF32LE>;
127template class elf::LLDDwarfObj<ELF32BE>;
128template class elf::LLDDwarfObj<ELF64LE>;
129template class elf::LLDDwarfObj<ELF64BE>;
130