DWARF.cpp
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//===- DWARF.cpp ----------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The -gdb-index option instructs the linker to emit a .gdb_index section.
// The section contains information to make gdb startup faster.
// The format of the section is described at
// https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html.
//
//===----------------------------------------------------------------------===//
#include "DWARF.h"
#include "Symbols.h"
#include "Target.h"
#include "lld/Common/Memory.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
#include "llvm/Object/ELFObjectFile.h"
using namespace llvm;
using namespace llvm::object;
using namespace lld;
using namespace lld::elf;
template <class ELFT> LLDDwarfObj<ELFT>::LLDDwarfObj(ObjFile<ELFT> *obj) {
// Get the ELF sections to retrieve sh_flags. See the SHF_GROUP comment below.
ArrayRef<typename ELFT::Shdr> objSections =
CHECK(obj->getObj().sections(), obj);
assert(objSections.size() == obj->getSections().size());
for (auto it : llvm::enumerate(obj->getSections())) {
InputSectionBase *sec = it.value();
if (!sec)
continue;
if (LLDDWARFSection *m =
StringSwitch<LLDDWARFSection *>(sec->name)
.Case(".debug_addr", &addrSection)
.Case(".debug_gnu_pubnames", &gnuPubnamesSection)
.Case(".debug_gnu_pubtypes", &gnuPubtypesSection)
.Case(".debug_loclists", &loclistsSection)
.Case(".debug_ranges", &rangesSection)
.Case(".debug_rnglists", &rnglistsSection)
.Case(".debug_str_offsets", &strOffsetsSection)
.Case(".debug_line", &lineSection)
.Default(nullptr)) {
m->Data = toStringRef(sec->data());
m->sec = sec;
continue;
}
if (sec->name == ".debug_abbrev")
abbrevSection = toStringRef(sec->data());
else if (sec->name == ".debug_str")
strSection = toStringRef(sec->data());
else if (sec->name == ".debug_line_str")
lineStrSection = toStringRef(sec->data());
else if (sec->name == ".debug_info" &&
!(objSections[it.index()].sh_flags & ELF::SHF_GROUP)) {
// In DWARF v5, -fdebug-types-section places type units in .debug_info
// sections in COMDAT groups. They are not compile units and thus should
// be ignored for .gdb_index/diagnostics purposes.
//
// We use a simple heuristic: the compile unit does not have the SHF_GROUP
// flag. If we place compile units in COMDAT groups in the future, we may
// need to perform a lightweight parsing. We drop the SHF_GROUP flag when
// the InputSection was created, so we need to retrieve sh_flags from the
// associated ELF section header.
infoSection.Data = toStringRef(sec->data());
infoSection.sec = sec;
}
}
}
namespace {
template <class RelTy> struct LLDRelocationResolver {
// In the ELF ABIs, S sepresents the value of the symbol in the relocation
// entry. For Rela, the addend is stored as part of the relocation entry.
static uint64_t resolve(object::RelocationRef ref, uint64_t s,
uint64_t /* A */) {
return s + ref.getRawDataRefImpl().p;
}
};
template <class ELFT> struct LLDRelocationResolver<Elf_Rel_Impl<ELFT, false>> {
// For Rel, the addend A is supplied by the caller.
static uint64_t resolve(object::RelocationRef /*Ref*/, uint64_t s,
uint64_t a) {
return s + a;
}
};
} // namespace
// Find if there is a relocation at Pos in Sec. The code is a bit
// more complicated than usual because we need to pass a section index
// to llvm since it has no idea about InputSection.
template <class ELFT>
template <class RelTy>
Optional<RelocAddrEntry>
LLDDwarfObj<ELFT>::findAux(const InputSectionBase &sec, uint64_t pos,
ArrayRef<RelTy> rels) const {
auto it =
partition_point(rels, [=](const RelTy &a) { return a.r_offset < pos; });
if (it == rels.end() || it->r_offset != pos)
return None;
const RelTy &rel = *it;
const ObjFile<ELFT> *file = sec.getFile<ELFT>();
uint32_t symIndex = rel.getSymbol(config->isMips64EL);
const typename ELFT::Sym &sym = file->template getELFSyms<ELFT>()[symIndex];
uint32_t secIndex = file->getSectionIndex(sym);
// An undefined symbol may be a symbol defined in a discarded section. We
// shall still resolve it. This is important for --gdb-index: the end address
// offset of an entry in .debug_ranges is relocated. If it is not resolved,
// its zero value will terminate the decoding of .debug_ranges prematurely.
Symbol &s = file->getRelocTargetSym(rel);
uint64_t val = 0;
if (auto *dr = dyn_cast<Defined>(&s))
val = dr->value;
DataRefImpl d;
d.p = getAddend<ELFT>(rel);
return RelocAddrEntry{secIndex, RelocationRef(d, nullptr),
val, Optional<object::RelocationRef>(),
0, LLDRelocationResolver<RelTy>::resolve};
}
template <class ELFT>
Optional<RelocAddrEntry> LLDDwarfObj<ELFT>::find(const llvm::DWARFSection &s,
uint64_t pos) const {
auto &sec = static_cast<const LLDDWARFSection &>(s);
if (sec.sec->areRelocsRela)
return findAux(*sec.sec, pos, sec.sec->template relas<ELFT>());
return findAux(*sec.sec, pos, sec.sec->template rels<ELFT>());
}
template class elf::LLDDwarfObj<ELF32LE>;
template class elf::LLDDwarfObj<ELF32BE>;
template class elf::LLDDwarfObj<ELF64LE>;
template class elf::LLDDwarfObj<ELF64BE>;