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TargetLoweringObjectFileImpl.cpp
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TargetLoweringObjectFileImpl.cpp
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//===- llvm/CodeGen/TargetLoweringObjectFileImpl.cpp - Object File Info ---===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements classes used to handle lowerings specific to common
// object file formats.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Triple.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/CodeGen/BasicBlockSectionUtils.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineModuleInfoImpls.h"
#include "llvm/IR/Comdat.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalObject.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Mangler.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PseudoProbe.h"
#include "llvm/IR/Type.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSectionGOFF.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCSectionXCOFF.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/ProfileData/InstrProf.h"
#include "llvm/Support/Base64.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include <cassert>
#include <string>
using namespace llvm;
using namespace dwarf;
static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
StringRef &Section) {
SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags;
M.getModuleFlagsMetadata(ModuleFlags);
for (const auto &MFE: ModuleFlags) {
// Ignore flags with 'Require' behaviour.
if (MFE.Behavior == Module::Require)
continue;
StringRef Key = MFE.Key->getString();
if (Key == "Objective-C Image Info Version") {
Version = mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();
} else if (Key == "Objective-C Garbage Collection" ||
Key == "Objective-C GC Only" ||
Key == "Objective-C Is Simulated" ||
Key == "Objective-C Class Properties" ||
Key == "Objective-C Image Swift Version") {
Flags |= mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue();
} else if (Key == "Objective-C Image Info Section") {
Section = cast<MDString>(MFE.Val)->getString();
}
// Backend generates L_OBJC_IMAGE_INFO from Swift ABI version + major + minor +
// "Objective-C Garbage Collection".
else if (Key == "Swift ABI Version") {
Flags |= (mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue()) << 8;
} else if (Key == "Swift Major Version") {
Flags |= (mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue()) << 24;
} else if (Key == "Swift Minor Version") {
Flags |= (mdconst::extract<ConstantInt>(MFE.Val)->getZExtValue()) << 16;
}
}
}
//===----------------------------------------------------------------------===//
// ELF
//===----------------------------------------------------------------------===//
TargetLoweringObjectFileELF::TargetLoweringObjectFileELF() {
SupportDSOLocalEquivalentLowering = true;
}
void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
const TargetMachine &TgtM) {
TargetLoweringObjectFile::Initialize(Ctx, TgtM);
CodeModel::Model CM = TgtM.getCodeModel();
InitializeELF(TgtM.Options.UseInitArray);
switch (TgtM.getTargetTriple().getArch()) {
case Triple::arm:
case Triple::armeb:
case Triple::thumb:
case Triple::thumbeb:
if (Ctx.getAsmInfo()->getExceptionHandlingType() == ExceptionHandling::ARM)
break;
// Fallthrough if not using EHABI
[[fallthrough]];
case Triple::ppc:
case Triple::ppcle:
case Triple::x86:
PersonalityEncoding = isPositionIndependent()
? dwarf::DW_EH_PE_indirect |
dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4
: dwarf::DW_EH_PE_absptr;
LSDAEncoding = isPositionIndependent()
? dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4
: dwarf::DW_EH_PE_absptr;
TTypeEncoding = isPositionIndependent()
? dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4
: dwarf::DW_EH_PE_absptr;
break;
case Triple::x86_64:
if (isPositionIndependent()) {
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
((CM == CodeModel::Small || CM == CodeModel::Medium)
? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
LSDAEncoding = dwarf::DW_EH_PE_pcrel |
(CM == CodeModel::Small
? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
((CM == CodeModel::Small || CM == CodeModel::Medium)
? dwarf::DW_EH_PE_sdata4 : dwarf::DW_EH_PE_sdata8);
} else {
PersonalityEncoding =
(CM == CodeModel::Small || CM == CodeModel::Medium)
? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
LSDAEncoding = (CM == CodeModel::Small)
? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
TTypeEncoding = (CM == CodeModel::Small)
? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_absptr;
}
break;
case Triple::hexagon:
PersonalityEncoding = dwarf::DW_EH_PE_absptr;
LSDAEncoding = dwarf::DW_EH_PE_absptr;
TTypeEncoding = dwarf::DW_EH_PE_absptr;
if (isPositionIndependent()) {
PersonalityEncoding |= dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel;
LSDAEncoding |= dwarf::DW_EH_PE_pcrel;
TTypeEncoding |= dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel;
}
break;
case Triple::aarch64:
case Triple::aarch64_be:
case Triple::aarch64_32:
// The small model guarantees static code/data size < 4GB, but not where it
// will be in memory. Most of these could end up >2GB away so even a signed
// pc-relative 32-bit address is insufficient, theoretically.
if (isPositionIndependent()) {
// ILP32 uses sdata4 instead of sdata8
if (TgtM.getTargetTriple().getEnvironment() == Triple::GNUILP32) {
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
} else {
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata8;
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata8;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata8;
}
} else {
PersonalityEncoding = dwarf::DW_EH_PE_absptr;
LSDAEncoding = dwarf::DW_EH_PE_absptr;
TTypeEncoding = dwarf::DW_EH_PE_absptr;
}
break;
case Triple::lanai:
LSDAEncoding = dwarf::DW_EH_PE_absptr;
PersonalityEncoding = dwarf::DW_EH_PE_absptr;
TTypeEncoding = dwarf::DW_EH_PE_absptr;
break;
case Triple::mips:
case Triple::mipsel:
case Triple::mips64:
case Triple::mips64el:
// MIPS uses indirect pointer to refer personality functions and types, so
// that the eh_frame section can be read-only. DW.ref.personality will be
// generated for relocation.
PersonalityEncoding = dwarf::DW_EH_PE_indirect;
// FIXME: The N64 ABI probably ought to use DW_EH_PE_sdata8 but we can't
// identify N64 from just a triple.
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
// We don't support PC-relative LSDA references in GAS so we use the default
// DW_EH_PE_absptr for those.
// FreeBSD must be explicit about the data size and using pcrel since it's
// assembler/linker won't do the automatic conversion that the Linux tools
// do.
if (TgtM.getTargetTriple().isOSFreeBSD()) {
PersonalityEncoding |= dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
}
break;
case Triple::ppc64:
case Triple::ppc64le:
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_udata8;
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_udata8;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_udata8;
break;
case Triple::sparcel:
case Triple::sparc:
if (isPositionIndependent()) {
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
} else {
LSDAEncoding = dwarf::DW_EH_PE_absptr;
PersonalityEncoding = dwarf::DW_EH_PE_absptr;
TTypeEncoding = dwarf::DW_EH_PE_absptr;
}
CallSiteEncoding = dwarf::DW_EH_PE_udata4;
break;
case Triple::riscv32:
case Triple::riscv64:
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
CallSiteEncoding = dwarf::DW_EH_PE_udata4;
break;
case Triple::sparcv9:
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
if (isPositionIndependent()) {
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
} else {
PersonalityEncoding = dwarf::DW_EH_PE_absptr;
TTypeEncoding = dwarf::DW_EH_PE_absptr;
}
break;
case Triple::systemz:
// All currently-defined code models guarantee that 4-byte PC-relative
// values will be in range.
if (isPositionIndependent()) {
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
} else {
PersonalityEncoding = dwarf::DW_EH_PE_absptr;
LSDAEncoding = dwarf::DW_EH_PE_absptr;
TTypeEncoding = dwarf::DW_EH_PE_absptr;
}
break;
case Triple::loongarch32:
case Triple::loongarch64:
LSDAEncoding = dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
PersonalityEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
TTypeEncoding = dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |
dwarf::DW_EH_PE_sdata4;
break;
default:
break;
}
}
void TargetLoweringObjectFileELF::getModuleMetadata(Module &M) {
SmallVector<GlobalValue *, 4> Vec;
collectUsedGlobalVariables(M, Vec, false);
for (GlobalValue *GV : Vec)
if (auto *GO = dyn_cast<GlobalObject>(GV))
Used.insert(GO);
}
void TargetLoweringObjectFileELF::emitModuleMetadata(MCStreamer &Streamer,
Module &M) const {
auto &C = getContext();
if (NamedMDNode *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
auto *S = C.getELFSection(".linker-options", ELF::SHT_LLVM_LINKER_OPTIONS,
ELF::SHF_EXCLUDE);
Streamer.switchSection(S);
for (const auto *Operand : LinkerOptions->operands()) {
if (cast<MDNode>(Operand)->getNumOperands() != 2)
report_fatal_error("invalid llvm.linker.options");
for (const auto &Option : cast<MDNode>(Operand)->operands()) {
Streamer.emitBytes(cast<MDString>(Option)->getString());
Streamer.emitInt8(0);
}
}
}
if (NamedMDNode *DependentLibraries = M.getNamedMetadata("llvm.dependent-libraries")) {
auto *S = C.getELFSection(".deplibs", ELF::SHT_LLVM_DEPENDENT_LIBRARIES,
ELF::SHF_MERGE | ELF::SHF_STRINGS, 1);
Streamer.switchSection(S);
for (const auto *Operand : DependentLibraries->operands()) {
Streamer.emitBytes(
cast<MDString>(cast<MDNode>(Operand)->getOperand(0))->getString());
Streamer.emitInt8(0);
}
}
if (NamedMDNode *FuncInfo = M.getNamedMetadata(PseudoProbeDescMetadataName)) {
// Emit a descriptor for every function including functions that have an
// available external linkage. We may not want this for imported functions
// that has code in another thinLTO module but we don't have a good way to
// tell them apart from inline functions defined in header files. Therefore
// we put each descriptor in a separate comdat section and rely on the
// linker to deduplicate.
for (const auto *Operand : FuncInfo->operands()) {
const auto *MD = cast<MDNode>(Operand);
auto *GUID = mdconst::dyn_extract<ConstantInt>(MD->getOperand(0));
auto *Hash = mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
auto *Name = cast<MDString>(MD->getOperand(2));
auto *S = C.getObjectFileInfo()->getPseudoProbeDescSection(
TM->getFunctionSections() ? Name->getString() : StringRef());
Streamer.switchSection(S);
Streamer.emitInt64(GUID->getZExtValue());
Streamer.emitInt64(Hash->getZExtValue());
Streamer.emitULEB128IntValue(Name->getString().size());
Streamer.emitBytes(Name->getString());
}
}
if (NamedMDNode *LLVMStats = M.getNamedMetadata("llvm.stats")) {
// Emit the metadata for llvm statistics into .llvm_stats section, which is
// formatted as a list of key/value pair, the value is base64 encoded.
auto *S = C.getObjectFileInfo()->getLLVMStatsSection();
Streamer.switchSection(S);
for (const auto *Operand : LLVMStats->operands()) {
const auto *MD = cast<MDNode>(Operand);
assert(MD->getNumOperands() % 2 == 0 &&
("Operand num should be even for a list of key/value pair"));
for (size_t I = 0; I < MD->getNumOperands(); I += 2) {
// Encode the key string size.
auto *Key = cast<MDString>(MD->getOperand(I));
Streamer.emitULEB128IntValue(Key->getString().size());
Streamer.emitBytes(Key->getString());
// Encode the value into a Base64 string.
std::string Value = encodeBase64(
Twine(mdconst::dyn_extract<ConstantInt>(MD->getOperand(I + 1))
->getZExtValue())
.str());
Streamer.emitULEB128IntValue(Value.size());
Streamer.emitBytes(Value);
}
}
}
unsigned Version = 0;
unsigned Flags = 0;
StringRef Section;
GetObjCImageInfo(M, Version, Flags, Section);
if (!Section.empty()) {
auto *S = C.getELFSection(Section, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
Streamer.switchSection(S);
Streamer.emitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));
Streamer.emitInt32(Version);
Streamer.emitInt32(Flags);
Streamer.addBlankLine();
}
emitCGProfileMetadata(Streamer, M);
}
MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
const GlobalValue *GV, const TargetMachine &TM,
MachineModuleInfo *MMI) const {
unsigned Encoding = getPersonalityEncoding();
if ((Encoding & 0x80) == DW_EH_PE_indirect)
return getContext().getOrCreateSymbol(StringRef("DW.ref.") +
TM.getSymbol(GV)->getName());
if ((Encoding & 0x70) == DW_EH_PE_absptr)
return TM.getSymbol(GV);
report_fatal_error("We do not support this DWARF encoding yet!");
}
void TargetLoweringObjectFileELF::emitPersonalityValue(
MCStreamer &Streamer, const DataLayout &DL, const MCSymbol *Sym) const {
SmallString<64> NameData("DW.ref.");
NameData += Sym->getName();
MCSymbolELF *Label =
cast<MCSymbolELF>(getContext().getOrCreateSymbol(NameData));
Streamer.emitSymbolAttribute(Label, MCSA_Hidden);
Streamer.emitSymbolAttribute(Label, MCSA_Weak);
unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
MCSection *Sec = getContext().getELFNamedSection(".data", Label->getName(),
ELF::SHT_PROGBITS, Flags, 0);
unsigned Size = DL.getPointerSize();
Streamer.switchSection(Sec);
Streamer.emitValueToAlignment(DL.getPointerABIAlignment(0));
Streamer.emitSymbolAttribute(Label, MCSA_ELF_TypeObject);
const MCExpr *E = MCConstantExpr::create(Size, getContext());
Streamer.emitELFSize(Label, E);
Streamer.emitLabel(Label);
Streamer.emitSymbolValue(Sym, Size);
}
const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
MachineModuleInfo *MMI, MCStreamer &Streamer) const {
if (Encoding & DW_EH_PE_indirect) {
MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", TM);
// Add information about the stub reference to ELFMMI so that the stub
// gets emitted by the asmprinter.
MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
if (!StubSym.getPointer()) {
MCSymbol *Sym = TM.getSymbol(GV);
StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
}
return TargetLoweringObjectFile::
getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
Encoding & ~DW_EH_PE_indirect, Streamer);
}
return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, TM,
MMI, Streamer);
}
static SectionKind getELFKindForNamedSection(StringRef Name, SectionKind K) {
// N.B.: The defaults used in here are not the same ones used in MC.
// We follow gcc, MC follows gas. For example, given ".section .eh_frame",
// both gas and MC will produce a section with no flags. Given
// section(".eh_frame") gcc will produce:
//
// .section .eh_frame,"a",@progbits
if (Name == getInstrProfSectionName(IPSK_covmap, Triple::ELF,
/*AddSegmentInfo=*/false) ||
Name == getInstrProfSectionName(IPSK_covfun, Triple::ELF,
/*AddSegmentInfo=*/false) ||
Name == ".llvmbc" || Name == ".llvmcmd")
return SectionKind::getMetadata();
if (Name.empty() || Name[0] != '.') return K;
// Default implementation based on some magic section names.
if (Name == ".bss" ||
Name.startswith(".bss.") ||
Name.startswith(".gnu.linkonce.b.") ||
Name.startswith(".llvm.linkonce.b.") ||
Name == ".sbss" ||
Name.startswith(".sbss.") ||
Name.startswith(".gnu.linkonce.sb.") ||
Name.startswith(".llvm.linkonce.sb."))
return SectionKind::getBSS();
if (Name == ".tdata" ||
Name.startswith(".tdata.") ||
Name.startswith(".gnu.linkonce.td.") ||
Name.startswith(".llvm.linkonce.td."))
return SectionKind::getThreadData();
if (Name == ".tbss" ||
Name.startswith(".tbss.") ||
Name.startswith(".gnu.linkonce.tb.") ||
Name.startswith(".llvm.linkonce.tb."))
return SectionKind::getThreadBSS();
return K;
}
static bool hasPrefix(StringRef SectionName, StringRef Prefix) {
return SectionName.consume_front(Prefix) &&
(SectionName.empty() || SectionName[0] == '.');
}
static unsigned getELFSectionType(StringRef Name, SectionKind K) {
// Use SHT_NOTE for section whose name starts with ".note" to allow
// emitting ELF notes from C variable declaration.
// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77609
if (Name.startswith(".note"))
return ELF::SHT_NOTE;
if (hasPrefix(Name, ".init_array"))
return ELF::SHT_INIT_ARRAY;
if (hasPrefix(Name, ".fini_array"))
return ELF::SHT_FINI_ARRAY;
if (hasPrefix(Name, ".preinit_array"))
return ELF::SHT_PREINIT_ARRAY;
if (hasPrefix(Name, ".llvm.offloading"))
return ELF::SHT_LLVM_OFFLOADING;
if (K.isBSS() || K.isThreadBSS())
return ELF::SHT_NOBITS;
return ELF::SHT_PROGBITS;
}
static unsigned getELFSectionFlags(SectionKind K) {
unsigned Flags = 0;
if (!K.isMetadata() && !K.isExclude())
Flags |= ELF::SHF_ALLOC;
if (K.isExclude())
Flags |= ELF::SHF_EXCLUDE;
if (K.isText())
Flags |= ELF::SHF_EXECINSTR;
if (K.isExecuteOnly())
Flags |= ELF::SHF_ARM_PURECODE;
if (K.isWriteable())
Flags |= ELF::SHF_WRITE;
if (K.isThreadLocal())
Flags |= ELF::SHF_TLS;
if (K.isMergeableCString() || K.isMergeableConst())
Flags |= ELF::SHF_MERGE;
if (K.isMergeableCString())
Flags |= ELF::SHF_STRINGS;
return Flags;
}
static const Comdat *getELFComdat(const GlobalValue *GV) {
const Comdat *C = GV->getComdat();
if (!C)
return nullptr;
if (C->getSelectionKind() != Comdat::Any &&
C->getSelectionKind() != Comdat::NoDeduplicate)
report_fatal_error("ELF COMDATs only support SelectionKind::Any and "
"SelectionKind::NoDeduplicate, '" +
C->getName() + "' cannot be lowered.");
return C;
}
static const MCSymbolELF *getLinkedToSymbol(const GlobalObject *GO,
const TargetMachine &TM) {
MDNode *MD = GO->getMetadata(LLVMContext::MD_associated);
if (!MD)
return nullptr;
const MDOperand &Op = MD->getOperand(0);
if (!Op.get())
return nullptr;
auto *VM = dyn_cast<ValueAsMetadata>(Op);
if (!VM)
report_fatal_error("MD_associated operand is not ValueAsMetadata");
auto *OtherGV = dyn_cast<GlobalValue>(VM->getValue());
return OtherGV ? dyn_cast<MCSymbolELF>(TM.getSymbol(OtherGV)) : nullptr;
}
static unsigned getEntrySizeForKind(SectionKind Kind) {
if (Kind.isMergeable1ByteCString())
return 1;
else if (Kind.isMergeable2ByteCString())
return 2;
else if (Kind.isMergeable4ByteCString())
return 4;
else if (Kind.isMergeableConst4())
return 4;
else if (Kind.isMergeableConst8())
return 8;
else if (Kind.isMergeableConst16())
return 16;
else if (Kind.isMergeableConst32())
return 32;
else {
// We shouldn't have mergeable C strings or mergeable constants that we
// didn't handle above.
assert(!Kind.isMergeableCString() && "unknown string width");
assert(!Kind.isMergeableConst() && "unknown data width");
return 0;
}
}
/// Return the section prefix name used by options FunctionsSections and
/// DataSections.
static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
if (Kind.isText())
return ".text";
if (Kind.isReadOnly())
return ".rodata";
if (Kind.isBSS())
return ".bss";
if (Kind.isThreadData())
return ".tdata";
if (Kind.isThreadBSS())
return ".tbss";
if (Kind.isData())
return ".data";
if (Kind.isReadOnlyWithRel())
return ".data.rel.ro";
llvm_unreachable("Unknown section kind");
}
static SmallString<128>
getELFSectionNameForGlobal(const GlobalObject *GO, SectionKind Kind,
Mangler &Mang, const TargetMachine &TM,
unsigned EntrySize, bool UniqueSectionName) {
SmallString<128> Name;
if (Kind.isMergeableCString()) {
// We also need alignment here.
// FIXME: this is getting the alignment of the character, not the
// alignment of the global!
Align Alignment = GO->getParent()->getDataLayout().getPreferredAlign(
cast<GlobalVariable>(GO));
std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
Name = SizeSpec + utostr(Alignment.value());
} else if (Kind.isMergeableConst()) {
Name = ".rodata.cst";
Name += utostr(EntrySize);
} else {
Name = getSectionPrefixForGlobal(Kind);
}
bool HasPrefix = false;
if (const auto *F = dyn_cast<Function>(GO)) {
if (std::optional<StringRef> Prefix = F->getSectionPrefix()) {
raw_svector_ostream(Name) << '.' << *Prefix;
HasPrefix = true;
}
}
if (UniqueSectionName) {
Name.push_back('.');
TM.getNameWithPrefix(Name, GO, Mang, /*MayAlwaysUsePrivate*/true);
} else if (HasPrefix)
// For distinguishing between .text.${text-section-prefix}. (with trailing
// dot) and .text.${function-name}
Name.push_back('.');
return Name;
}
namespace {
class LoweringDiagnosticInfo : public DiagnosticInfo {
const Twine &Msg;
public:
LoweringDiagnosticInfo(const Twine &DiagMsg,
DiagnosticSeverity Severity = DS_Error)
: DiagnosticInfo(DK_Lowering, Severity), Msg(DiagMsg) {}
void print(DiagnosticPrinter &DP) const override { DP << Msg; }
};
}
/// Calculate an appropriate unique ID for a section, and update Flags,
/// EntrySize and NextUniqueID where appropriate.
static unsigned
calcUniqueIDUpdateFlagsAndSize(const GlobalObject *GO, StringRef SectionName,
SectionKind Kind, const TargetMachine &TM,
MCContext &Ctx, Mangler &Mang, unsigned &Flags,
unsigned &EntrySize, unsigned &NextUniqueID,
const bool Retain, const bool ForceUnique) {
// Increment uniqueID if we are forced to emit a unique section.
// This works perfectly fine with section attribute or pragma section as the
// sections with the same name are grouped together by the assembler.
if (ForceUnique)
return NextUniqueID++;
// A section can have at most one associated section. Put each global with
// MD_associated in a unique section.
const bool Associated = GO->getMetadata(LLVMContext::MD_associated);
if (Associated) {
Flags |= ELF::SHF_LINK_ORDER;
return NextUniqueID++;
}
if (Retain) {
if (TM.getTargetTriple().isOSSolaris())
Flags |= ELF::SHF_SUNW_NODISCARD;
else if (Ctx.getAsmInfo()->useIntegratedAssembler() ||
Ctx.getAsmInfo()->binutilsIsAtLeast(2, 36))
Flags |= ELF::SHF_GNU_RETAIN;
return NextUniqueID++;
}
// If two symbols with differing sizes end up in the same mergeable section
// that section can be assigned an incorrect entry size. To avoid this we
// usually put symbols of the same size into distinct mergeable sections with
// the same name. Doing so relies on the ",unique ," assembly feature. This
// feature is not avalible until bintuils version 2.35
// (https://sourceware.org/bugzilla/show_bug.cgi?id=25380).
const bool SupportsUnique = Ctx.getAsmInfo()->useIntegratedAssembler() ||
Ctx.getAsmInfo()->binutilsIsAtLeast(2, 35);
if (!SupportsUnique) {
Flags &= ~ELF::SHF_MERGE;
EntrySize = 0;
return MCContext::GenericSectionID;
}
const bool SymbolMergeable = Flags & ELF::SHF_MERGE;
const bool SeenSectionNameBefore =
Ctx.isELFGenericMergeableSection(SectionName);
// If this is the first ocurrence of this section name, treat it as the
// generic section
if (!SymbolMergeable && !SeenSectionNameBefore)
return MCContext::GenericSectionID;
// Symbols must be placed into sections with compatible entry sizes. Generate
// unique sections for symbols that have not been assigned to compatible
// sections.
const auto PreviousID =
Ctx.getELFUniqueIDForEntsize(SectionName, Flags, EntrySize);
if (PreviousID)
return *PreviousID;
// If the user has specified the same section name as would be created
// implicitly for this symbol e.g. .rodata.str1.1, then we don't need
// to unique the section as the entry size for this symbol will be
// compatible with implicitly created sections.
SmallString<128> ImplicitSectionNameStem =
getELFSectionNameForGlobal(GO, Kind, Mang, TM, EntrySize, false);
if (SymbolMergeable &&
Ctx.isELFImplicitMergeableSectionNamePrefix(SectionName) &&
SectionName.startswith(ImplicitSectionNameStem))
return MCContext::GenericSectionID;
// We have seen this section name before, but with different flags or entity
// size. Create a new unique ID.
return NextUniqueID++;
}
static MCSection *selectExplicitSectionGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM,
MCContext &Ctx, Mangler &Mang, unsigned &NextUniqueID,
bool Retain, bool ForceUnique) {
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("relro-section") && Kind.isReadOnlyWithRel()) {
SectionName = Attrs.getAttribute("relro-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 = "";
bool IsComdat = false;
unsigned Flags = getELFSectionFlags(Kind);
if (const Comdat *C = getELFComdat(GO)) {
Group = C->getName();
IsComdat = C->getSelectionKind() == Comdat::Any;
Flags |= ELF::SHF_GROUP;
}
unsigned EntrySize = getEntrySizeForKind(Kind);
const unsigned UniqueID = calcUniqueIDUpdateFlagsAndSize(
GO, SectionName, Kind, TM, Ctx, Mang, Flags, EntrySize, NextUniqueID,
Retain, ForceUnique);
const MCSymbolELF *LinkedToSym = getLinkedToSymbol(GO, TM);
MCSectionELF *Section = Ctx.getELFSection(
SectionName, getELFSectionType(SectionName, Kind), Flags, EntrySize,
Group, IsComdat, UniqueID, LinkedToSym);
// 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->getLinkedToSymbol() == LinkedToSym &&
"Associated symbol mismatch between sections");
if (!(Ctx.getAsmInfo()->useIntegratedAssembler() ||
Ctx.getAsmInfo()->binutilsIsAtLeast(2, 35))) {
// If we are using GNU as before 2.35, then this symbol might have
// been placed in an incompatible mergeable section. Emit an error if this
// is the case to avoid creating broken output.
if ((Section->getFlags() & ELF::SHF_MERGE) &&
(Section->getEntrySize() != getEntrySizeForKind(Kind)))
GO->getContext().diagnose(LoweringDiagnosticInfo(
"Symbol '" + GO->getName() + "' from module '" +
(GO->getParent() ? GO->getParent()->getSourceFileName() : "unknown") +
"' required a section with entry-size=" +
Twine(getEntrySizeForKind(Kind)) + " but was placed in section '" +
SectionName + "' with entry-size=" + Twine(Section->getEntrySize()) +
": Explicit assignment by pragma or attribute of an incompatible "
"symbol to this section?"));
}
return Section;
}
MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
return selectExplicitSectionGlobal(GO, Kind, TM, getContext(), getMangler(),
NextUniqueID, Used.count(GO),
/* ForceUnique = */false);
}
static MCSectionELF *selectELFSectionForGlobal(
MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
const TargetMachine &TM, bool EmitUniqueSection, unsigned Flags,
unsigned *NextUniqueID, const MCSymbolELF *AssociatedSymbol) {
StringRef Group = "";
bool IsComdat = false;
if (const Comdat *C = getELFComdat(GO)) {
Flags |= ELF::SHF_GROUP;
Group = C->getName();
IsComdat = C->getSelectionKind() == Comdat::Any;
}
// Get the section entry size based on the kind.
unsigned EntrySize = getEntrySizeForKind(Kind);
bool UniqueSectionName = false;
unsigned UniqueID = MCContext::GenericSectionID;
if (EmitUniqueSection) {
if (TM.getUniqueSectionNames()) {
UniqueSectionName = true;
} else {
UniqueID = *NextUniqueID;
(*NextUniqueID)++;
}
}
SmallString<128> Name = getELFSectionNameForGlobal(
GO, Kind, Mang, TM, EntrySize, UniqueSectionName);
// Use 0 as the unique ID for execute-only text.
if (Kind.isExecuteOnly())
UniqueID = 0;
return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
EntrySize, Group, IsComdat, UniqueID,
AssociatedSymbol);
}
static MCSection *selectELFSectionForGlobal(
MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
const TargetMachine &TM, bool Retain, bool EmitUniqueSection,
unsigned Flags, unsigned *NextUniqueID) {
const MCSymbolELF *LinkedToSym = getLinkedToSymbol(GO, TM);
if (LinkedToSym) {
EmitUniqueSection = true;
Flags |= ELF::SHF_LINK_ORDER;
}
if (Retain) {
if (TM.getTargetTriple().isOSSolaris()) {
EmitUniqueSection = true;
Flags |= ELF::SHF_SUNW_NODISCARD;
} else if (Ctx.getAsmInfo()->useIntegratedAssembler() ||
Ctx.getAsmInfo()->binutilsIsAtLeast(2, 36)) {
EmitUniqueSection = true;
Flags |= ELF::SHF_GNU_RETAIN;
}
}
MCSectionELF *Section = selectELFSectionForGlobal(
Ctx, GO, Kind, Mang, TM, EmitUniqueSection, Flags,
NextUniqueID, LinkedToSym);
assert(Section->getLinkedToSymbol() == LinkedToSym);
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();
return selectELFSectionForGlobal(getContext(), GO, Kind, getMangler(), TM,
Used.count(GO), EmitUniqueSection, Flags,
&NextUniqueID);
}
MCSection *TargetLoweringObjectFileELF::getUniqueSectionForFunction(
const Function &F, const TargetMachine &TM) const {
SectionKind Kind = SectionKind::getText();
unsigned Flags = getELFSectionFlags(Kind);
// If the function's section names is pre-determined via pragma or a
// section attribute, call selectExplicitSectionGlobal.
if (F.hasSection() || F.hasFnAttribute("implicit-section-name"))
return selectExplicitSectionGlobal(
&F, Kind, TM, getContext(), getMangler(), NextUniqueID,
Used.count(&F), /* ForceUnique = */true);
else
return selectELFSectionForGlobal(
getContext(), &F, Kind, getMangler(), TM, Used.count(&F),
/*EmitUniqueSection=*/true, Flags, &NextUniqueID);
}
MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
const Function &F, const TargetMachine &TM) const {
// If the function can be removed, produce a unique section so that
// the table doesn't prevent the removal.
const Comdat *C = F.getComdat();
bool EmitUniqueSection = TM.getFunctionSections() || C;
if (!EmitUniqueSection)
return ReadOnlySection;
return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
getMangler(), TM, EmitUniqueSection,
ELF::SHF_ALLOC, &NextUniqueID,
/* AssociatedSymbol */ nullptr);
}
MCSection *TargetLoweringObjectFileELF::getSectionForLSDA(
const Function &F, const MCSymbol &FnSym, const TargetMachine &TM) const {
// If neither COMDAT nor function sections, use the monolithic LSDA section.
// Re-use this path if LSDASection is null as in the Arm EHABI.
if (!LSDASection || (!F.hasComdat() && !TM.getFunctionSections()))
return LSDASection;
const auto *LSDA = cast<MCSectionELF>(LSDASection);
unsigned Flags = LSDA->getFlags();
const MCSymbolELF *LinkedToSym = nullptr;
StringRef Group;
bool IsComdat = false;
if (const Comdat *C = getELFComdat(&F)) {
Flags |= ELF::SHF_GROUP;
Group = C->getName();
IsComdat = C->getSelectionKind() == Comdat::Any;
}
// Use SHF_LINK_ORDER to facilitate --gc-sections if we can use GNU ld>=2.36
// or LLD, which support mixed SHF_LINK_ORDER & non-SHF_LINK_ORDER.
if (TM.getFunctionSections() &&
(getContext().getAsmInfo()->useIntegratedAssembler() &&
getContext().getAsmInfo()->binutilsIsAtLeast(2, 36))) {
Flags |= ELF::SHF_LINK_ORDER;
LinkedToSym = cast<MCSymbolELF>(&FnSym);
}
// Append the function name as the suffix like GCC, assuming
// -funique-section-names applies to .gcc_except_table sections.
return getContext().getELFSection(