1 //===- DWARF.cpp ----------------------------------------------------------===//
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
7 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
19 #include "lld/Common/Memory.h"
20 #include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
21 #include "llvm/Object/ELFObjectFile.h"
24 using namespace llvm::object;
26 using namespace lld::elf;
28 template <class ELFT> LLDDwarfObj<ELFT>::LLDDwarfObj(ObjFile<ELFT> *obj) {
29 // Get the ELF sections to retrieve sh_flags. See the SHF_GROUP comment below.
30 ArrayRef<typename ELFT::Shdr> objSections =
31 CHECK(obj->getObj().sections(), obj);
32 assert(objSections.size() == obj->getSections().size());
33 for (auto it : llvm::enumerate(obj->getSections())) {
34 InputSectionBase *sec = it.value();
38 if (LLDDWARFSection *m =
39 StringSwitch<LLDDWARFSection *>(sec->name)
40 .Case(".debug_addr", &addrSection)
41 .Case(".debug_gnu_pubnames", &gnuPubnamesSection)
42 .Case(".debug_gnu_pubtypes", &gnuPubtypesSection)
43 .Case(".debug_loclists", &loclistsSection)
44 .Case(".debug_ranges", &rangesSection)
45 .Case(".debug_rnglists", &rnglistsSection)
46 .Case(".debug_str_offsets", &strOffsetsSection)
47 .Case(".debug_line", &lineSection)
49 m->Data = toStringRef(sec->data());
54 if (sec->name == ".debug_abbrev")
55 abbrevSection = toStringRef(sec->data());
56 else if (sec->name == ".debug_str")
57 strSection = toStringRef(sec->data());
58 else if (sec->name == ".debug_line_str")
59 lineStrSection = toStringRef(sec->data());
60 else if (sec->name == ".debug_info" &&
61 !(objSections[it.index()].sh_flags & ELF::SHF_GROUP)) {
62 // In DWARF v5, -fdebug-types-section places type units in .debug_info
63 // sections in COMDAT groups. They are not compile units and thus should
64 // be ignored for .gdb_index/diagnostics purposes.
66 // We use a simple heuristic: the compile unit does not have the SHF_GROUP
67 // flag. If we place compile units in COMDAT groups in the future, we may
68 // need to perform a lightweight parsing. We drop the SHF_GROUP flag when
69 // the InputSection was created, so we need to retrieve sh_flags from the
70 // associated ELF section header.
71 infoSection.Data = toStringRef(sec->data());
72 infoSection.sec = sec;
78 template <class RelTy> struct LLDRelocationResolver {
79 // In the ELF ABIs, S sepresents the value of the symbol in the relocation
80 // entry. For Rela, the addend is stored as part of the relocation entry.
81 static uint64_t resolve(object::RelocationRef ref, uint64_t s,
83 return s + ref.getRawDataRefImpl().p;
87 template <class ELFT> struct LLDRelocationResolver<Elf_Rel_Impl<ELFT, false>> {
88 // For Rel, the addend A is supplied by the caller.
89 static uint64_t resolve(object::RelocationRef /*Ref*/, uint64_t s,
96 // Find if there is a relocation at Pos in Sec. The code is a bit
97 // more complicated than usual because we need to pass a section index
98 // to llvm since it has no idea about InputSection.
100 template <class RelTy>
101 Optional<RelocAddrEntry>
102 LLDDwarfObj<ELFT>::findAux(const InputSectionBase &sec, uint64_t pos,
103 ArrayRef<RelTy> rels) const {
105 partition_point(rels, [=](const RelTy &a) { return a.r_offset < pos; });
106 if (it == rels.end() || it->r_offset != pos)
108 const RelTy &rel = *it;
110 const ObjFile<ELFT> *file = sec.getFile<ELFT>();
111 uint32_t symIndex = rel.getSymbol(config->isMips64EL);
112 const typename ELFT::Sym &sym = file->template getELFSyms<ELFT>()[symIndex];
113 uint32_t secIndex = file->getSectionIndex(sym);
115 // An undefined symbol may be a symbol defined in a discarded section. We
116 // shall still resolve it. This is important for --gdb-index: the end address
117 // offset of an entry in .debug_ranges is relocated. If it is not resolved,
118 // its zero value will terminate the decoding of .debug_ranges prematurely.
119 Symbol &s = file->getRelocTargetSym(rel);
121 if (auto *dr = dyn_cast<Defined>(&s))
125 d.p = getAddend<ELFT>(rel);
126 return RelocAddrEntry{secIndex, RelocationRef(d, nullptr),
127 val, Optional<object::RelocationRef>(),
128 0, LLDRelocationResolver<RelTy>::resolve};
131 template <class ELFT>
132 Optional<RelocAddrEntry> LLDDwarfObj<ELFT>::find(const llvm::DWARFSection &s,
133 uint64_t pos) const {
134 auto &sec = static_cast<const LLDDWARFSection &>(s);
135 if (sec.sec->areRelocsRela)
136 return findAux(*sec.sec, pos, sec.sec->template relas<ELFT>());
137 return findAux(*sec.sec, pos, sec.sec->template rels<ELFT>());
140 template class elf::LLDDwarfObj<ELF32LE>;
141 template class elf::LLDDwarfObj<ELF32BE>;
142 template class elf::LLDDwarfObj<ELF64LE>;
143 template class elf::LLDDwarfObj<ELF64BE>;