forked from OSchip/llvm-project
104 lines
4.8 KiB
C++
104 lines
4.8 KiB
C++
//===- GdbIndex.cpp -------------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// File contains classes for implementation of --gdb-index command line option.
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//
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// If that option is used, linker should emit a .gdb_index section that allows
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// debugger to locate and read .dwo files, containing neccessary debug
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// information.
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// More information about implementation can be found in DWARF specification,
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// latest version is available at http://dwarfstd.org.
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//
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// .gdb_index section format:
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// (Information is based on/taken from
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// https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html (*))
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//
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// A mapped index consists of several areas, laid out in order:
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// 1) The file header.
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// 2) "The CU (compilation unit) list. This is a sequence of pairs of 64-bit
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// little-endian values, sorted by the CU offset. The first element in each
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// pair is the offset of a CU in the .debug_info section. The second element
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// in each pair is the length of that CU. References to a CU elsewhere in the
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// map are done using a CU index, which is just the 0-based index into this
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// table. Note that if there are type CUs, then conceptually CUs and type CUs
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// form a single list for the purposes of CU indices."(*)
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// 3) The types CU list. Depricated as .debug_types does not appear in the DWARF
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// v5 specification.
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// 4) The address area. The address area is a sequence of address
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// entries, where each entrie contains low address, high address and CU
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// index.
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// 5) "The symbol table. This is an open-addressed hash table. The size of the
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// hash table is always a power of 2. Each slot in the hash table consists of
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// a pair of offset_type values. The first value is the offset of the
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// symbol's name in the constant pool. The second value is the offset of the
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// CU vector in the constant pool."(*)
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// 6) "The constant pool. This is simply a bunch of bytes. It is organized so
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// that alignment is correct: CU vectors are stored first, followed by
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// strings." (*)
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//
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// For constructing the .gdb_index section following steps should be performed:
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// 1) For file header nothing special should be done. It contains the offsets to
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// the areas below.
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// 2) Scan the compilation unit headers of the .debug_info sections to build a
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// list of compilation units.
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// 3) CU Types are no longer needed as DWARF skeleton type units never made it
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// into the standard. lld does nothing to support parsing of .debug_types
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// and generates empty types CU area in .gdb_index section.
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// 4) Address area entries are extracted from DW_TAG_compile_unit DIEs of
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// .debug_info sections.
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// 5) For building the symbol table linker extracts the public names from the
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// .debug_gnu_pubnames and .debug_gnu_pubtypes sections. Then it builds the
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// hashtable in according to .gdb_index format specification.
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// 6) Constant pool is populated at the same time as symbol table.
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//
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// Current version of implementation has 1, 2, 3 steps. So it writes .gdb_index
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// header and list of compilation units. Since we so not plan to support types
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// CU list area, it is also empty and so far is "implemented".
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// Other data areas are not yet implemented.
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//===----------------------------------------------------------------------===//
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#include "GdbIndex.h"
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#include "llvm/DebugInfo/DWARF/DWARFContext.h"
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using namespace llvm;
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using namespace llvm::object;
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template <class ELFT>
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std::vector<std::pair<typename ELFT::uint, typename ELFT::uint>>
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lld::elf::readCuList(InputSection<ELFT> *DebugInfoSec) {
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typedef typename ELFT::uint uintX_t;
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std::unique_ptr<DWARFContext> Dwarf;
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if (Expected<std::unique_ptr<object::ObjectFile>> Obj =
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object::ObjectFile::createObjectFile(DebugInfoSec->getFile()->MB))
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Dwarf.reset(new DWARFContextInMemory(*Obj.get()));
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if (!Dwarf) {
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error(getFilename(DebugInfoSec->getFile()) +
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": error creating DWARF context");
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return {};
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}
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std::vector<std::pair<uintX_t, uintX_t>> Ret;
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for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf->compile_units())
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Ret.push_back(
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{DebugInfoSec->OutSecOff + CU->getOffset(), CU->getLength() + 4});
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return Ret;
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}
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template std::vector<std::pair<uint32_t, uint32_t>>
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lld::elf::readCuList<ELF32LE>(InputSection<ELF32LE> *);
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template std::vector<std::pair<uint32_t, uint32_t>>
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lld::elf::readCuList<ELF32BE>(InputSection<ELF32BE> *);
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template std::vector<std::pair<uint64_t, uint64_t>>
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lld::elf::readCuList<ELF64LE>(InputSection<ELF64LE> *);
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template std::vector<std::pair<uint64_t, uint64_t>>
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lld::elf::readCuList<ELF64BE>(InputSection<ELF64BE> *);
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