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Produce a single string table in a ELF .o
Normally an ELF .o has two string tables, one for symbols, one for section names. With the scheme of naming sections like ".text.foo" where foo is a symbol, there is a big potential saving in using a single one. Building llvm+clang+lld with master and with this patch the results were: master: 193,267,008 bytes patch: 186,107,952 bytes master non unique section names: 183,260,192 bytes patch non unique section names: 183,118,632 bytes So using non usique saves 10,006,816 bytes, and the patch saves 7,159,056 while still using distinct names for the sections. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238073 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
parent
e00c0df2c4
commit
7c4f3dcc5e
@ -107,7 +107,6 @@ class ELFObjectWriter : public MCObjectWriter {
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llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
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Relocations;
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StringTableBuilder ShStrTabBuilder;
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/// @}
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/// @name Symbol Table Data
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@ -129,8 +128,8 @@ class ELFObjectWriter : public MCObjectWriter {
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unsigned StringTableIndex;
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// This holds the .symtab section index.
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unsigned SymbolTableIndex;
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unsigned ShstrtabIndex;
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// This holds the .symtab_shndx section index.
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unsigned SymtabShndxSectionIndex = 0;
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// Sections in the order they are to be output in the section table.
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std::vector<MCSectionELF *> SectionTable;
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@ -157,7 +156,6 @@ class ELFObjectWriter : public MCObjectWriter {
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WeakrefUsedInReloc.clear();
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Renames.clear();
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Relocations.clear();
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ShStrTabBuilder.clear();
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StrTabBuilder.clear();
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FileSymbolData.clear();
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LocalSymbolData.clear();
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@ -224,7 +222,6 @@ class ELFObjectWriter : public MCObjectWriter {
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MCSectionELF *createRelocationSection(MCContext &Ctx,
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const MCSectionELF &Sec);
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const MCSectionELF *createSectionHeaderStringTable();
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const MCSectionELF *createStringTable(MCContext &Ctx);
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void ExecutePostLayoutBinding(MCAssembler &Asm,
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@ -261,7 +258,7 @@ class ELFObjectWriter : public MCObjectWriter {
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unsigned ELFObjectWriter::addToSectionTable(MCSectionELF *Sec) {
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SectionTable.push_back(Sec);
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ShStrTabBuilder.add(Sec->getSectionName());
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StrTabBuilder.add(Sec->getSectionName());
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return SectionTable.size();
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}
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@ -395,8 +392,8 @@ void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
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Write16(0);
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// e_shstrndx = Section # of '.shstrtab'
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assert(ShstrtabIndex < ELF::SHN_LORESERVE);
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Write16(ShstrtabIndex);
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assert(StringTableIndex < ELF::SHN_LORESERVE);
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Write16(StringTableIndex);
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}
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uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
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@ -541,13 +538,7 @@ void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
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void ELFObjectWriter::writeSymbolTable(MCContext &Ctx,
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const MCAsmLayout &Layout,
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SectionOffsetsTy &SectionOffsets) {
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unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
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// Symbol table
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MCSectionELF *SymtabSection =
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Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
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SymtabSection->setAlignment(is64Bit() ? 8 : 4);
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SymbolTableIndex = addToSectionTable(SymtabSection);
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MCSectionELF *SymtabSection = SectionTable[SymbolTableIndex - 1];
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// The string table must be emitted first because we need the index
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// into the string table for all the symbol names.
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@ -599,14 +590,14 @@ void ELFObjectWriter::writeSymbolTable(MCContext &Ctx,
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SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
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ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
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if (ShndxIndexes.empty())
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if (ShndxIndexes.empty()) {
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assert(SymtabShndxSectionIndex == 0);
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return;
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}
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assert(SymtabShndxSectionIndex != 0);
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SecStart = OS.tell();
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MCSectionELF *SymtabShndxSection =
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Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
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addToSectionTable(SymtabShndxSection);
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SymtabShndxSection->setAlignment(4);
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MCSectionELF *SymtabShndxSection = SectionTable[SymtabShndxSectionIndex - 1];
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for (uint32_t Index : ShndxIndexes)
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write(Index);
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SecEnd = OS.tell();
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@ -917,6 +908,14 @@ void ELFObjectWriter::computeSymbolTable(
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MCAssembler &Asm, const MCAsmLayout &Layout,
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const SectionIndexMapTy &SectionIndexMap,
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const RevGroupMapTy &RevGroupMap) {
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MCContext &Ctx = Asm.getContext();
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// Symbol table
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unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
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MCSectionELF *SymtabSection =
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Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
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SymtabSection->setAlignment(is64Bit() ? 8 : 4);
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SymbolTableIndex = addToSectionTable(SymtabSection);
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// FIXME: Is this the correct place to do this?
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// FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
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if (NeedsGOT) {
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@ -928,6 +927,7 @@ void ELFObjectWriter::computeSymbolTable(
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}
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// Add the data for the symbols.
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bool HasLargeSectionIndex = false;
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for (const MCSymbol &Symbol : Asm.symbols()) {
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MCSymbolData &SD = Symbol.getData();
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@ -959,10 +959,13 @@ void ELFObjectWriter::computeSymbolTable(
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assert(!Local);
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MSD.SectionIndex = ELF::SHN_COMMON;
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} else if (BaseSymbol->isUndefined()) {
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if (isSignature && !Used)
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if (isSignature && !Used) {
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MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
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else
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if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
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HasLargeSectionIndex = true;
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} else {
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MSD.SectionIndex = ELF::SHN_UNDEF;
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}
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if (!Used && WeakrefUsed)
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MCELF::SetBinding(SD, ELF::STB_WEAK);
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} else {
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@ -970,6 +973,8 @@ void ELFObjectWriter::computeSymbolTable(
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static_cast<const MCSectionELF&>(BaseSymbol->getSection());
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MSD.SectionIndex = SectionIndexMap.lookup(&Section);
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assert(MSD.SectionIndex && "Invalid section index!");
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if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
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HasLargeSectionIndex = true;
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}
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// The @@@ in symbol version is replaced with @ in undefined symbols and @@
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@ -1023,6 +1028,13 @@ void ELFObjectWriter::computeSymbolTable(
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ExternalSymbolData.push_back(MSD);
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}
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if (HasLargeSectionIndex) {
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MCSectionELF *SymtabShndxSection =
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Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
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SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
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SymtabShndxSection->setAlignment(4);
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}
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for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
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StrTabBuilder.add(*i);
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@ -1227,17 +1239,8 @@ void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
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}
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}
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const MCSectionELF *ELFObjectWriter::createSectionHeaderStringTable() {
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const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
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ShStrTabBuilder.finalize(StringTableBuilder::ELF);
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OS << ShStrTabBuilder.data();
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return ShstrtabSection;
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}
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const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
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MCSectionELF *StrtabSection =
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Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
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StringTableIndex = addToSectionTable(StrtabSection);
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MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
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OS << StrTabBuilder.data();
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return StrtabSection;
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}
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@ -1285,7 +1288,7 @@ void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
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Section.getType() == ELF::SHT_ARM_EXIDX)
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sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
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WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
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WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
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Section.getType(), Section.getFlags(), 0, Offset, Size,
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sh_link, sh_info, Section.getAlignment(),
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Section.getEntrySize());
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@ -1328,9 +1331,9 @@ void ELFObjectWriter::writeSectionHeader(
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void ELFObjectWriter::WriteObject(MCAssembler &Asm,
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const MCAsmLayout &Layout) {
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MCContext &Ctx = Asm.getContext();
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MCSectionELF *ShstrtabSection =
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Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
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ShstrtabIndex = addToSectionTable(ShstrtabSection);
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MCSectionELF *StrtabSection =
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Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
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StringTableIndex = addToSectionTable(StrtabSection);
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RevGroupMapTy RevGroupMap;
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SectionIndexMapTy SectionIndexMap;
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@ -1426,13 +1429,6 @@ void ELFObjectWriter::WriteObject(MCAssembler &Asm,
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SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
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}
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{
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uint64_t SecStart = OS.tell();
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const MCSectionELF *Sec = createSectionHeaderStringTable();
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uint64_t SecEnd = OS.tell();
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SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
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}
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uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
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uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
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WriteZeros(Padding);
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@ -11,16 +11,16 @@
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// WINDOWS-NEXT: Arch: x86_64
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// Test that like gnu as we create text, data and bss by default. Also test
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// that shstrtab, symtab and strtab are listed.
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// that symtab and strtab are listed.
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// CHECK: Section {
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// CHECK: Name: .shstrtab
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// CHECK: Name: .strtab
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// CHECK-NEXT: Type: SHT_STRTAB
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// CHECK-NEXT: Flags [
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// CHECK-NEXT: ]
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// CHECK-NEXT: Address: 0x0
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// CHECK-NEXT: Offset:
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// CHECK-NEXT: Size: 44
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// CHECK-NEXT: Size: 34
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// CHECK-NEXT: Link: 0
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// CHECK-NEXT: Info: 0
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// CHECK-NEXT: AddressAlignment: 1
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@ -84,16 +84,3 @@
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// CHECK-NEXT: AddressAlignment: 8
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// CHECK-NEXT: EntrySize: 24
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// CHECK-NEXT: }
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// CHECK: Section {
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// CHECK: Name: .strtab
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// CHECK-NEXT: Type: SHT_STRTAB
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// CHECK-NEXT: Flags [
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// CHECK-NEXT: ]
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// CHECK-NEXT: Address: 0x0
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// CHECK-NEXT: Offset:
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// CHECK-NEXT: Size: 1
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// CHECK-NEXT: Link: 0
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// CHECK-NEXT: Info: 0
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// CHECK-NEXT: AddressAlignment: 1
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// CHECK-NEXT: EntrySize: 0
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// CHECK-NEXT: }
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@ -16,6 +16,6 @@ foobar:
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.Ltmp3:
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.size foobar, .Ltmp3-foobar
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// CHECK: Name: foobar (1)
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// CHECK: Name: bar (4)
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// CHECK: Name: foo (8)
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// CHECK: Name: foobar (16)
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// CHECK: Name: bar (19)
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// CHECK: Name: foo (23)
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