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 23 using namespace llvm; 24 using namespace llvm::object; 25 using namespace lld; 26 using namespace lld::elf; 27 28 template <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 57 namespace { 58 template <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 67 template <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. 79 template <class ELFT> 80 template <class RelTy> 81 Optional<RelocAddrEntry> 82 LLDDwarfObj<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 } 116 117 template <class ELFT> 118 Optional<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 } 125 126 template class elf::LLDDwarfObj<ELF32LE>; 127 template class elf::LLDDwarfObj<ELF32BE>; 128 template class elf::LLDDwarfObj<ELF64LE>; 129 template class elf::LLDDwarfObj<ELF64BE>; 130