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 // Get the ELF sections to retrieve sh_flags. See the SHF_GROUP comment below. 30 ArrayRef<typename ELFT::Shdr> objSections = obj->template getELFShdrs<ELFT>(); 31 assert(objSections.size() == obj->getSections().size()); 32 for (auto it : llvm::enumerate(obj->getSections())) { 33 InputSectionBase *sec = it.value(); 34 if (!sec) 35 continue; 36 37 if (LLDDWARFSection *m = 38 StringSwitch<LLDDWARFSection *>(sec->name) 39 .Case(".debug_addr", &addrSection) 40 .Case(".debug_gnu_pubnames", &gnuPubnamesSection) 41 .Case(".debug_gnu_pubtypes", &gnuPubtypesSection) 42 .Case(".debug_loclists", &loclistsSection) 43 .Case(".debug_ranges", &rangesSection) 44 .Case(".debug_rnglists", &rnglistsSection) 45 .Case(".debug_str_offsets", &strOffsetsSection) 46 .Case(".debug_line", &lineSection) 47 .Default(nullptr)) { 48 m->Data = toStringRef(sec->data()); 49 m->sec = sec; 50 continue; 51 } 52 53 if (sec->name == ".debug_abbrev") 54 abbrevSection = toStringRef(sec->data()); 55 else if (sec->name == ".debug_str") 56 strSection = toStringRef(sec->data()); 57 else if (sec->name == ".debug_line_str") 58 lineStrSection = toStringRef(sec->data()); 59 else if (sec->name == ".debug_info" && 60 !(objSections[it.index()].sh_flags & ELF::SHF_GROUP)) { 61 // In DWARF v5, -fdebug-types-section places type units in .debug_info 62 // sections in COMDAT groups. They are not compile units and thus should 63 // be ignored for .gdb_index/diagnostics purposes. 64 // 65 // We use a simple heuristic: the compile unit does not have the SHF_GROUP 66 // flag. If we place compile units in COMDAT groups in the future, we may 67 // need to perform a lightweight parsing. We drop the SHF_GROUP flag when 68 // the InputSection was created, so we need to retrieve sh_flags from the 69 // associated ELF section header. 70 infoSection.Data = toStringRef(sec->data()); 71 infoSection.sec = sec; 72 } 73 } 74 } 75 76 namespace { 77 template <class RelTy> struct LLDRelocationResolver { 78 // In the ELF ABIs, S sepresents the value of the symbol in the relocation 79 // entry. For Rela, the addend is stored as part of the relocation entry and 80 // is provided by the `findAux` method. 81 // In resolve() methods, the `type` and `offset` arguments would always be 0, 82 // because we don't set an owning object for the `RelocationRef` instance that 83 // we create in `findAux()`. 84 static uint64_t resolve(uint64_t /*type*/, uint64_t /*offset*/, uint64_t s, 85 uint64_t /*locData*/, int64_t addend) { 86 return s + addend; 87 } 88 }; 89 90 template <class ELFT> struct LLDRelocationResolver<Elf_Rel_Impl<ELFT, false>> { 91 // For Rel, the addend is extracted from the relocated location and is 92 // supplied by the caller. 93 static uint64_t resolve(uint64_t /*type*/, uint64_t /*offset*/, uint64_t s, 94 uint64_t locData, int64_t /*addend*/) { 95 return s + locData; 96 } 97 }; 98 } // namespace 99 100 // Find if there is a relocation at Pos in Sec. The code is a bit 101 // more complicated than usual because we need to pass a section index 102 // to llvm since it has no idea about InputSection. 103 template <class ELFT> 104 template <class RelTy> 105 Optional<RelocAddrEntry> 106 LLDDwarfObj<ELFT>::findAux(const InputSectionBase &sec, uint64_t pos, 107 ArrayRef<RelTy> rels) const { 108 auto it = 109 partition_point(rels, [=](const RelTy &a) { return a.r_offset < pos; }); 110 if (it == rels.end() || it->r_offset != pos) 111 return None; 112 const RelTy &rel = *it; 113 114 const ObjFile<ELFT> *file = sec.getFile<ELFT>(); 115 uint32_t symIndex = rel.getSymbol(config->isMips64EL); 116 const typename ELFT::Sym &sym = file->template getELFSyms<ELFT>()[symIndex]; 117 uint32_t secIndex = file->getSectionIndex(sym); 118 119 // An undefined symbol may be a symbol defined in a discarded section. We 120 // shall still resolve it. This is important for --gdb-index: the end address 121 // offset of an entry in .debug_ranges is relocated. If it is not resolved, 122 // its zero value will terminate the decoding of .debug_ranges prematurely. 123 Symbol &s = file->getRelocTargetSym(rel); 124 uint64_t val = 0; 125 if (auto *dr = dyn_cast<Defined>(&s)) 126 val = dr->value; 127 128 DataRefImpl d; 129 d.p = getAddend<ELFT>(rel); 130 return RelocAddrEntry{secIndex, RelocationRef(d, nullptr), 131 val, Optional<object::RelocationRef>(), 132 0, LLDRelocationResolver<RelTy>::resolve}; 133 } 134 135 template <class ELFT> 136 Optional<RelocAddrEntry> LLDDwarfObj<ELFT>::find(const llvm::DWARFSection &s, 137 uint64_t pos) const { 138 auto &sec = static_cast<const LLDDWARFSection &>(s); 139 const RelsOrRelas<ELFT> rels = sec.sec->template relsOrRelas<ELFT>(); 140 if (rels.areRelocsRel()) 141 return findAux(*sec.sec, pos, rels.rels); 142 return findAux(*sec.sec, pos, rels.relas); 143 } 144 145 template class elf::LLDDwarfObj<ELF32LE>; 146 template class elf::LLDDwarfObj<ELF32BE>; 147 template class elf::LLDDwarfObj<ELF64LE>; 148 template class elf::LLDDwarfObj<ELF64BE>; 149