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 = 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(); 35 if (!sec) 36 continue; 37 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) 48 .Default(nullptr)) { 49 m->Data = toStringRef(sec->data()); 50 m->sec = sec; 51 continue; 52 } 53 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. 65 // 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; 73 } 74 } 75 } 76 77 namespace { 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 and 81 // is provided by the `findAux` method. 82 // In resolve() methods, the `type` and `offset` arguments would always be 0, 83 // because we don't set an owning object for the `RelocationRef` instance that 84 // we create in `findAux()`. 85 static uint64_t resolve(uint64_t /*type*/, uint64_t /*offset*/, uint64_t s, 86 uint64_t /*locData*/, int64_t addend) { 87 return s + addend; 88 } 89 }; 90 91 template <class ELFT> struct LLDRelocationResolver<Elf_Rel_Impl<ELFT, false>> { 92 // For Rel, the addend is extracted from the relocated location and is 93 // supplied by the caller. 94 static uint64_t resolve(uint64_t /*type*/, uint64_t /*offset*/, uint64_t s, 95 uint64_t locData, int64_t /*addend*/) { 96 return s + locData; 97 } 98 }; 99 } // namespace 100 101 // Find if there is a relocation at Pos in Sec. The code is a bit 102 // more complicated than usual because we need to pass a section index 103 // to llvm since it has no idea about InputSection. 104 template <class ELFT> 105 template <class RelTy> 106 Optional<RelocAddrEntry> 107 LLDDwarfObj<ELFT>::findAux(const InputSectionBase &sec, uint64_t pos, 108 ArrayRef<RelTy> rels) const { 109 auto it = 110 partition_point(rels, [=](const RelTy &a) { return a.r_offset < pos; }); 111 if (it == rels.end() || it->r_offset != pos) 112 return None; 113 const RelTy &rel = *it; 114 115 const ObjFile<ELFT> *file = sec.getFile<ELFT>(); 116 uint32_t symIndex = rel.getSymbol(config->isMips64EL); 117 const typename ELFT::Sym &sym = file->template getELFSyms<ELFT>()[symIndex]; 118 uint32_t secIndex = file->getSectionIndex(sym); 119 120 // An undefined symbol may be a symbol defined in a discarded section. We 121 // shall still resolve it. This is important for --gdb-index: the end address 122 // offset of an entry in .debug_ranges is relocated. If it is not resolved, 123 // its zero value will terminate the decoding of .debug_ranges prematurely. 124 Symbol &s = file->getRelocTargetSym(rel); 125 uint64_t val = 0; 126 if (auto *dr = dyn_cast<Defined>(&s)) 127 val = dr->value; 128 129 DataRefImpl d; 130 d.p = getAddend<ELFT>(rel); 131 return RelocAddrEntry{secIndex, RelocationRef(d, nullptr), 132 val, Optional<object::RelocationRef>(), 133 0, LLDRelocationResolver<RelTy>::resolve}; 134 } 135 136 template <class ELFT> 137 Optional<RelocAddrEntry> LLDDwarfObj<ELFT>::find(const llvm::DWARFSection &s, 138 uint64_t pos) const { 139 auto &sec = static_cast<const LLDDWARFSection &>(s); 140 if (sec.sec->areRelocsRela) 141 return findAux(*sec.sec, pos, sec.sec->template relas<ELFT>()); 142 return findAux(*sec.sec, pos, sec.sec->template rels<ELFT>()); 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