MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
StringRef SectionName = GO->getSection();
// Infer section flags from the section name if we can.
Kind = getELFKindForNamedSection(SectionName, Kind);
StringRef Group = "";
unsigned Flags = getELFSectionFlags(Kind);
if (const Comdat *C = getELFComdat(GO)) {
Group = C->getName();
Flags |= ELF::SHF_GROUP;
}
// A section can have at most one associated section. Put each global with
// MD_associated in a unique section.
unsigned UniqueID = MCContext::GenericSectionID;
const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
if (AssociatedSymbol) {
UniqueID = NextUniqueID++;
Flags |= ELF::SHF_LINK_ORDER;
}
MCSectionELF *Section = getContext().getELFSection(
SectionName, getELFSectionType(SectionName, Kind), Flags,
/*EntrySize=*/0, Group, UniqueID, AssociatedSymbol);
// Make sure that we did not get some other section with incompatible sh_link.
// This should not be possible due to UniqueID code above.
assert(Section->getAssociatedSymbol() == AssociatedSymbol);
return Section;
}
MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
unsigned Flags = getELFSectionFlags(Kind);
// If we have -ffunction-section or -fdata-section then we should emit the
// global value to a uniqued section specifically for it.
bool EmitUniqueSection = false;
if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
if (Kind.isText())
EmitUniqueSection = TM.getFunctionSections();
else
EmitUniqueSection = TM.getDataSections();
}
EmitUniqueSection |= GO->hasComdat();
const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
if (AssociatedSymbol) {
EmitUniqueSection = true;
Flags |= ELF::SHF_LINK_ORDER;
}
MCSectionELF *Section = selectELFSectionForGlobal(
getContext(), GO, Kind, getMangler(), TM, EmitUniqueSection, Flags,
&NextUniqueID, AssociatedSymbol);
assert(Section->getAssociatedSymbol() == AssociatedSymbol);
return Section;
}
MCSectionELF *
ELFObjectWriter::createRelocationSection(MCContext &Ctx,
const MCSectionELF &Sec) {
if (Relocations[&Sec].empty())
return nullptr;
const StringRef SectionName = Sec.getSectionName();
std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
RelaSectionName += SectionName;
unsigned EntrySize;
if (hasRelocationAddend())
EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
else
EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
unsigned Flags = 0;
if (Sec.getFlags() & ELF::SHF_GROUP)
Flags = ELF::SHF_GROUP;
MCSectionELF *RelaSection = Ctx.createELFRelSection(
RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
Flags, EntrySize, Sec.getGroup(), &Sec);
RelaSection->setAlignment(is64Bit() ? 8 : 4);
return RelaSection;
}
MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
StringRef SectionName = GO->getSection();
// Check if '#pragma clang section' name is applicable.
// Note that pragma directive overrides -ffunction-section, -fdata-section
// and so section name is exactly as user specified and not uniqued.
const GlobalVariable *GV = dyn_cast<GlobalVariable>(GO);
if (GV && GV->hasImplicitSection()) {
auto Attrs = GV->getAttributes();
if (Attrs.hasAttribute("bss-section") && Kind.isBSS()) {
SectionName = Attrs.getAttribute("bss-section").getValueAsString();
} else if (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly()) {
SectionName = Attrs.getAttribute("rodata-section").getValueAsString();
} else if (Attrs.hasAttribute("data-section") && Kind.isData()) {
SectionName = Attrs.getAttribute("data-section").getValueAsString();
}
}
const Function *F = dyn_cast<Function>(GO);
if (F && F->hasFnAttribute("implicit-section-name")) {
SectionName = F->getFnAttribute("implicit-section-name").getValueAsString();
}
// Infer section flags from the section name if we can.
Kind = getELFKindForNamedSection(SectionName, Kind);
StringRef Group = "";
unsigned Flags = getELFSectionFlags(Kind);
if (const Comdat *C = getELFComdat(GO)) {
Group = C->getName();
Flags |= ELF::SHF_GROUP;
}
// A section can have at most one associated section. Put each global with
// MD_associated in a unique section.
unsigned UniqueID = MCContext::GenericSectionID;
const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
if (AssociatedSymbol) {
UniqueID = NextUniqueID++;
Flags |= ELF::SHF_LINK_ORDER;
}
MCSectionELF *Section = getContext().getELFSection(
SectionName, getELFSectionType(SectionName, Kind), Flags,
/*EntrySize=*/0, Group, UniqueID, AssociatedSymbol);
// Make sure that we did not get some other section with incompatible sh_link.
// This should not be possible due to UniqueID code above.
assert(Section->getAssociatedSymbol() == AssociatedSymbol);
return Section;
}
void MipsRegInfoRecord::EmitMipsOptionRecord() {
MCAssembler &MCA = Streamer->getAssembler();
MipsTargetStreamer *MTS =
static_cast<MipsTargetStreamer *>(Streamer->getTargetStreamer());
Streamer->PushSection();
// We need to distinguish between N64 and the rest because at the moment
// we don't emit .Mips.options for other ELFs other than N64.
// Since .reginfo has the same information as .Mips.options (ODK_REGINFO),
// we can use the same abstraction (MipsRegInfoRecord class) to handle both.
if (MTS->getABI().IsN64()) {
// The EntrySize value of 1 seems strange since the records are neither
// 1-byte long nor fixed length but it matches the value GAS emits.
MCSectionELF *Sec =
Context.getELFSection(".MIPS.options", ELF::SHT_MIPS_OPTIONS,
ELF::SHF_ALLOC | ELF::SHF_MIPS_NOSTRIP, 1, "");
MCA.registerSection(*Sec);
Sec->setAlignment(8);
Streamer->SwitchSection(Sec);
Streamer->EmitIntValue(ELF::ODK_REGINFO, 1); // kind
Streamer->EmitIntValue(40, 1); // size
Streamer->EmitIntValue(0, 2); // section
Streamer->EmitIntValue(0, 4); // info
Streamer->EmitIntValue(ri_gprmask, 4);
Streamer->EmitIntValue(0, 4); // pad
Streamer->EmitIntValue(ri_cprmask[0], 4);
Streamer->EmitIntValue(ri_cprmask[1], 4);
Streamer->EmitIntValue(ri_cprmask[2], 4);
Streamer->EmitIntValue(ri_cprmask[3], 4);
Streamer->EmitIntValue(ri_gp_value, 8);
} else {
MCSectionELF *Sec = Context.getELFSection(".reginfo", ELF::SHT_MIPS_REGINFO,
ELF::SHF_ALLOC, 24, "");
MCA.registerSection(*Sec);
Sec->setAlignment(MTS->getABI().IsN32() ? 8 : 4);
Streamer->SwitchSection(Sec);
Streamer->EmitIntValue(ri_gprmask, 4);
Streamer->EmitIntValue(ri_cprmask[0], 4);
Streamer->EmitIntValue(ri_cprmask[1], 4);
Streamer->EmitIntValue(ri_cprmask[2], 4);
Streamer->EmitIntValue(ri_cprmask[3], 4);
assert((ri_gp_value & 0xffffffff) == ri_gp_value);
Streamer->EmitIntValue(ri_gp_value, 4);
}
Streamer->PopSection();
}
/// HasCommonSymbols - True if this section holds common symbols, this is
/// indicated on the ELF object file by a symbol with SHN_COMMON section
/// header index.
static bool HasCommonSymbols(const MCSectionELF &S) {
// FIXME: this is wrong, a common symbol can be in .data for example.
if (StringRef(S.getSectionName()).startswith(".gnu.linkonce."))
return true;
return false;
}
void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
uint32_t GroupSymbolIndex, uint64_t Offset,
uint64_t Size, const MCSectionELF &Section) {
uint64_t sh_link = 0;
uint64_t sh_info = 0;
switch(Section.getType()) {
default:
// Nothing to do.
break;
case ELF::SHT_DYNAMIC:
llvm_unreachable("SHT_DYNAMIC in a relocatable object");
case ELF::SHT_REL:
case ELF::SHT_RELA: {
sh_link = SymbolTableIndex;
assert(sh_link && ".symtab not found");
const MCSection *InfoSection = Section.getAssociatedSection();
sh_info = SectionIndexMap.lookup(cast<MCSectionELF>(InfoSection));
break;
}
case ELF::SHT_SYMTAB:
case ELF::SHT_DYNSYM:
sh_link = StringTableIndex;
sh_info = LastLocalSymbolIndex;
break;
case ELF::SHT_SYMTAB_SHNDX:
sh_link = SymbolTableIndex;
break;
case ELF::SHT_GROUP:
sh_link = SymbolTableIndex;
sh_info = GroupSymbolIndex;
break;
}
if (Section.getFlags() & ELF::SHF_LINK_ORDER) {
const MCSymbol *Sym = Section.getAssociatedSymbol();
const MCSectionELF *Sec = cast<MCSectionELF>(&Sym->getSection());
sh_link = SectionIndexMap.lookup(Sec);
}
WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
Section.getType(), Section.getFlags(), 0, Offset, Size,
sh_link, sh_info, Section.getAlignment(),
Section.getEntrySize());
}
void ELFObjectWriter::computeSymbolTable(
MCAssembler &Asm, const MCAsmLayout &Layout,
const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
SectionOffsetsTy &SectionOffsets) {
MCContext &Ctx = Asm.getContext();
SymbolTableWriter Writer(*this, is64Bit());
// Symbol table
unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
MCSectionELF *SymtabSection =
Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
SymtabSection->setAlignment(is64Bit() ? 8 : 4);
SymbolTableIndex = addToSectionTable(SymtabSection);
align(SymtabSection->getAlignment());
uint64_t SecStart = getStream().tell();
// The first entry is the undefined symbol entry.
Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
std::vector<ELFSymbolData> LocalSymbolData;
std::vector<ELFSymbolData> ExternalSymbolData;
// Add the data for the symbols.
bool HasLargeSectionIndex = false;
for (const MCSymbol &S : Asm.symbols()) {
const auto &Symbol = cast<MCSymbolELF>(S);
bool Used = Symbol.isUsedInReloc();
bool WeakrefUsed = Symbol.isWeakrefUsedInReloc();
bool isSignature = Symbol.isSignature();
if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
Renames.count(&Symbol)))
continue;
if (Symbol.isTemporary() && Symbol.isUndefined()) {
Ctx.reportError(SMLoc(), "Undefined temporary symbol");
continue;
}
ELFSymbolData MSD;
MSD.Symbol = cast<MCSymbolELF>(&Symbol);
bool Local = Symbol.getBinding() == ELF::STB_LOCAL;
assert(Local || !Symbol.isTemporary());
if (Symbol.isAbsolute()) {
MSD.SectionIndex = ELF::SHN_ABS;
} else if (Symbol.isCommon()) {
assert(!Local);
MSD.SectionIndex = ELF::SHN_COMMON;
} else if (Symbol.isUndefined()) {
if (isSignature && !Used) {
MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
HasLargeSectionIndex = true;
} else {
MSD.SectionIndex = ELF::SHN_UNDEF;
}
} else {
const MCSectionELF &Section =
static_cast<const MCSectionELF &>(Symbol.getSection());
MSD.SectionIndex = SectionIndexMap.lookup(&Section);
assert(MSD.SectionIndex && "Invalid section index!");
if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
HasLargeSectionIndex = true;
}
// The @@@ in symbol version is replaced with @ in undefined symbols and @@
// in defined ones.
//
// FIXME: All name handling should be done before we get to the writer,
// including dealing with GNU-style version suffixes. Fixing this isn't
// trivial.
//
// We thus have to be careful to not perform the symbol version replacement
// blindly:
//
// The ELF format is used on Windows by the MCJIT engine. Thus, on
// Windows, the ELFObjectWriter can encounter symbols mangled using the MS
// Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
// C++ name mangling can legally have "@@@" as a sub-string. In that case,
// the EFLObjectWriter should not interpret the "@@@" sub-string as
// specifying GNU-style symbol versioning. The ELFObjectWriter therefore
// checks for the MSVC C++ name mangling prefix which is either "?", "@?",
// "__imp_?" or "__imp_@?".
//
// It would have been interesting to perform the MS mangling prefix check
// only when the target triple is of the form *-pc-windows-elf. But, it
// seems that this information is not easily accessible from the
// ELFObjectWriter.
StringRef Name = Symbol.getName();
SmallString<32> Buf;
if (!Name.startswith("?") && !Name.startswith("@?") &&
!Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
// This symbol isn't following the MSVC C++ name mangling convention. We
// can thus safely interpret the @@@ in symbol names as specifying symbol
// versioning.
size_t Pos = Name.find("@@@");
if (Pos != StringRef::npos) {
Buf += Name.substr(0, Pos);
unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
Buf += Name.substr(Pos + Skip);
Name = VersionSymSaver.save(Buf.c_str());
}
}
// Sections have their own string table
if (Symbol.getType() != ELF::STT_SECTION) {
MSD.Name = Name;
StrTabBuilder.add(Name);
}
if (Local)
LocalSymbolData.push_back(MSD);
else
ExternalSymbolData.push_back(MSD);
}
// This holds the .symtab_shndx section index.
unsigned SymtabShndxSectionIndex = 0;
if (HasLargeSectionIndex) {
MCSectionELF *SymtabShndxSection =
Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
SymtabShndxSection->setAlignment(4);
}
ArrayRef<std::string> FileNames = Asm.getFileNames();
for (const std::string &Name : FileNames)
StrTabBuilder.add(Name);
StrTabBuilder.finalize();
// File symbols are emitted first and handled separately from normal symbols,
// i.e. a non-STT_FILE symbol with the same name may appear.
for (const std::string &Name : FileNames)
Writer.writeSymbol(StrTabBuilder.getOffset(Name),
ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
ELF::SHN_ABS, true);
// Symbols are required to be in lexicographic order.
array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
// Set the symbol indices. Local symbols must come before all other
// symbols with non-local bindings.
unsigned Index = FileNames.size() + 1;
for (ELFSymbolData &MSD : LocalSymbolData) {
unsigned StringIndex = MSD.Symbol->getType() == ELF::STT_SECTION
? 0
: StrTabBuilder.getOffset(MSD.Name);
MSD.Symbol->setIndex(Index++);
writeSymbol(Writer, StringIndex, MSD, Layout);
}
// Write the symbol table entries.
LastLocalSymbolIndex = Index;
for (ELFSymbolData &MSD : ExternalSymbolData) {
unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
MSD.Symbol->setIndex(Index++);
writeSymbol(Writer, StringIndex, MSD, Layout);
assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
}
uint64_t SecEnd = getStream().tell();
SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
if (ShndxIndexes.empty()) {
assert(SymtabShndxSectionIndex == 0);
return;
}
assert(SymtabShndxSectionIndex != 0);
SecStart = getStream().tell();
const MCSectionELF *SymtabShndxSection =
SectionTable[SymtabShndxSectionIndex - 1];
for (uint32_t Index : ShndxIndexes)
write(Index);
SecEnd = getStream().tell();
SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
}
void ELFObjectWriter::writeObject(MCAssembler &Asm,
const MCAsmLayout &Layout) {
MCContext &Ctx = Asm.getContext();
MCSectionELF *StrtabSection =
Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
StringTableIndex = addToSectionTable(StrtabSection);
RevGroupMapTy RevGroupMap;
SectionIndexMapTy SectionIndexMap;
std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
// Write out the ELF header ...
writeHeader(Asm);
// ... then the sections ...
SectionOffsetsTy SectionOffsets;
std::vector<MCSectionELF *> Groups;
std::vector<MCSectionELF *> Relocations;
for (MCSection &Sec : Asm) {
MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
align(Section.getAlignment());
// Remember the offset into the file for this section.
uint64_t SecStart = getStream().tell();
const MCSymbolELF *SignatureSymbol = Section.getGroup();
writeSectionData(Asm, Section, Layout);
uint64_t SecEnd = getStream().tell();
SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
if (SignatureSymbol) {
Asm.registerSymbol(*SignatureSymbol);
unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
if (!GroupIdx) {
MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
GroupIdx = addToSectionTable(Group);
Group->setAlignment(4);
Groups.push_back(Group);
}
std::vector<const MCSectionELF *> &Members =
GroupMembers[SignatureSymbol];
Members.push_back(&Section);
if (RelSection)
Members.push_back(RelSection);
}
SectionIndexMap[&Section] = addToSectionTable(&Section);
if (RelSection) {
SectionIndexMap[RelSection] = addToSectionTable(RelSection);
Relocations.push_back(RelSection);
}
}
for (MCSectionELF *Group : Groups) {
align(Group->getAlignment());
// Remember the offset into the file for this section.
uint64_t SecStart = getStream().tell();
const MCSymbol *SignatureSymbol = Group->getGroup();
assert(SignatureSymbol);
write(uint32_t(ELF::GRP_COMDAT));
for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
uint32_t SecIndex = SectionIndexMap.lookup(Member);
write(SecIndex);
}
uint64_t SecEnd = getStream().tell();
SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
}
// Compute symbol table information.
computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
for (MCSectionELF *RelSection : Relocations) {
align(RelSection->getAlignment());
// Remember the offset into the file for this section.
uint64_t SecStart = getStream().tell();
writeRelocations(Asm,
cast<MCSectionELF>(*RelSection->getAssociatedSection()));
uint64_t SecEnd = getStream().tell();
SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
}
{
uint64_t SecStart = getStream().tell();
const MCSectionELF *Sec = createStringTable(Ctx);
uint64_t SecEnd = getStream().tell();
SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
}
uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
align(NaturalAlignment);
const uint64_t SectionHeaderOffset = getStream().tell();
// ... then the section header table ...
writeSectionHeader(Layout, SectionIndexMap, SectionOffsets);
uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
? (uint16_t)ELF::SHN_UNDEF
: SectionTable.size() + 1;
if (sys::IsLittleEndianHost != IsLittleEndian)
sys::swapByteOrder(NumSections);
unsigned NumSectionsOffset;
if (is64Bit()) {
uint64_t Val = SectionHeaderOffset;
if (sys::IsLittleEndianHost != IsLittleEndian)
sys::swapByteOrder(Val);
getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
offsetof(ELF::Elf64_Ehdr, e_shoff));
NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
} else {
uint32_t Val = SectionHeaderOffset;
if (sys::IsLittleEndianHost != IsLittleEndian)
sys::swapByteOrder(Val);
getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
offsetof(ELF::Elf32_Ehdr, e_shoff));
NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
}
getStream().pwrite(reinterpret_cast<char *>(&NumSections),
sizeof(NumSections), NumSectionsOffset);
}
