| //===-- llvm/Target/TargetLoweringObjectFile.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/Target/TargetLoweringObjectFile.h" |
| #include "llvm/BinaryFormat/Dwarf.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/GlobalVariable.h" |
| #include "llvm/IR/Mangler.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/MC/MCAsmInfo.h" |
| #include "llvm/MC/MCContext.h" |
| #include "llvm/MC/MCExpr.h" |
| #include "llvm/MC/MCStreamer.h" |
| #include "llvm/MC/MCSymbol.h" |
| #include "llvm/MC/SectionKind.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Target/TargetMachine.h" |
| #include "llvm/Target/TargetOptions.h" |
| using namespace llvm; |
| |
| //===----------------------------------------------------------------------===// |
| // Generic Code |
| //===----------------------------------------------------------------------===// |
| |
| /// Initialize - this method must be called before any actual lowering is |
| /// done. This specifies the current context for codegen, and gives the |
| /// lowering implementations a chance to set up their default sections. |
| void TargetLoweringObjectFile::Initialize(MCContext &ctx, |
| const TargetMachine &TM) { |
| // `Initialize` can be called more than once. |
| delete Mang; |
| Mang = new Mangler(); |
| initMCObjectFileInfo(ctx, TM.isPositionIndependent(), |
| TM.getCodeModel() == CodeModel::Large); |
| |
| // Reset various EH DWARF encodings. |
| PersonalityEncoding = LSDAEncoding = TTypeEncoding = dwarf::DW_EH_PE_absptr; |
| CallSiteEncoding = dwarf::DW_EH_PE_uleb128; |
| |
| this->TM = &TM; |
| } |
| |
| TargetLoweringObjectFile::~TargetLoweringObjectFile() { |
| delete Mang; |
| } |
| |
| unsigned TargetLoweringObjectFile::getCallSiteEncoding() const { |
| // If target does not have LEB128 directives, we would need the |
| // call site encoding to be udata4 so that the alternative path |
| // for not having LEB128 directives could work. |
| if (!getContext().getAsmInfo()->hasLEB128Directives()) |
| return dwarf::DW_EH_PE_udata4; |
| return CallSiteEncoding; |
| } |
| |
| static bool isNullOrUndef(const Constant *C) { |
| // Check that the constant isn't all zeros or undefs. |
| if (C->isNullValue() || isa<UndefValue>(C)) |
| return true; |
| if (!isa<ConstantAggregate>(C)) |
| return false; |
| for (auto Operand : C->operand_values()) { |
| if (!isNullOrUndef(cast<Constant>(Operand))) |
| return false; |
| } |
| return true; |
| } |
| |
| static bool isSuitableForBSS(const GlobalVariable *GV) { |
| const Constant *C = GV->getInitializer(); |
| |
| // Must have zero initializer. |
| if (!isNullOrUndef(C)) |
| return false; |
| |
| // Leave constant zeros in readonly constant sections, so they can be shared. |
| if (GV->isConstant()) |
| return false; |
| |
| // If the global has an explicit section specified, don't put it in BSS. |
| if (GV->hasSection()) |
| return false; |
| |
| // Otherwise, put it in BSS! |
| return true; |
| } |
| |
| /// IsNullTerminatedString - Return true if the specified constant (which is |
| /// known to have a type that is an array of 1/2/4 byte elements) ends with a |
| /// nul value and contains no other nuls in it. Note that this is more general |
| /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings. |
| static bool IsNullTerminatedString(const Constant *C) { |
| // First check: is we have constant array terminated with zero |
| if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) { |
| unsigned NumElts = CDS->getNumElements(); |
| assert(NumElts != 0 && "Can't have an empty CDS"); |
| |
| if (CDS->getElementAsInteger(NumElts-1) != 0) |
| return false; // Not null terminated. |
| |
| // Verify that the null doesn't occur anywhere else in the string. |
| for (unsigned i = 0; i != NumElts-1; ++i) |
| if (CDS->getElementAsInteger(i) == 0) |
| return false; |
| return true; |
| } |
| |
| // Another possibility: [1 x i8] zeroinitializer |
| if (isa<ConstantAggregateZero>(C)) |
| return cast<ArrayType>(C->getType())->getNumElements() == 1; |
| |
| return false; |
| } |
| |
| MCSymbol *TargetLoweringObjectFile::getSymbolWithGlobalValueBase( |
| const GlobalValue *GV, StringRef Suffix, const TargetMachine &TM) const { |
| assert(!Suffix.empty()); |
| |
| SmallString<60> NameStr; |
| NameStr += GV->getParent()->getDataLayout().getPrivateGlobalPrefix(); |
| TM.getNameWithPrefix(NameStr, GV, *Mang); |
| NameStr.append(Suffix.begin(), Suffix.end()); |
| return getContext().getOrCreateSymbol(NameStr); |
| } |
| |
| MCSymbol *TargetLoweringObjectFile::getCFIPersonalitySymbol( |
| const GlobalValue *GV, const TargetMachine &TM, |
| MachineModuleInfo *MMI) const { |
| return TM.getSymbol(GV); |
| } |
| |
| void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer, |
| const DataLayout &, |
| const MCSymbol *Sym) const { |
| } |
| |
| void TargetLoweringObjectFile::emitCGProfileMetadata(MCStreamer &Streamer, |
| Module &M) const { |
| MCContext &C = getContext(); |
| SmallVector<Module::ModuleFlagEntry, 8> ModuleFlags; |
| M.getModuleFlagsMetadata(ModuleFlags); |
| |
| MDNode *CFGProfile = nullptr; |
| |
| for (const auto &MFE : ModuleFlags) { |
| StringRef Key = MFE.Key->getString(); |
| if (Key == "CG Profile") { |
| CFGProfile = cast<MDNode>(MFE.Val); |
| break; |
| } |
| } |
| |
| if (!CFGProfile) |
| return; |
| |
| auto GetSym = [this](const MDOperand &MDO) -> MCSymbol * { |
| if (!MDO) |
| return nullptr; |
| auto *V = cast<ValueAsMetadata>(MDO); |
| const Function *F = cast<Function>(V->getValue()->stripPointerCasts()); |
| if (F->hasDLLImportStorageClass()) |
| return nullptr; |
| return TM->getSymbol(F); |
| }; |
| |
| for (const auto &Edge : CFGProfile->operands()) { |
| MDNode *E = cast<MDNode>(Edge); |
| const MCSymbol *From = GetSym(E->getOperand(0)); |
| const MCSymbol *To = GetSym(E->getOperand(1)); |
| // Skip null functions. This can happen if functions are dead stripped after |
| // the CGProfile pass has been run. |
| if (!From || !To) |
| continue; |
| uint64_t Count = cast<ConstantAsMetadata>(E->getOperand(2)) |
| ->getValue() |
| ->getUniqueInteger() |
| .getZExtValue(); |
| Streamer.emitCGProfileEntry( |
| MCSymbolRefExpr::create(From, MCSymbolRefExpr::VK_None, C), |
| MCSymbolRefExpr::create(To, MCSymbolRefExpr::VK_None, C), Count); |
| } |
| } |
| |
| /// getKindForGlobal - This is a top-level target-independent classifier for |
| /// a global object. Given a global variable and information from the TM, this |
| /// function classifies the global in a target independent manner. This function |
| /// may be overridden by the target implementation. |
| SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalObject *GO, |
| const TargetMachine &TM){ |
| assert(!GO->isDeclarationForLinker() && |
| "Can only be used for global definitions"); |
| |
| // Functions are classified as text sections. |
| if (isa<Function>(GO)) |
| return SectionKind::getText(); |
| |
| // Basic blocks are classified as text sections. |
| if (isa<BasicBlock>(GO)) |
| return SectionKind::getText(); |
| |
| // Global variables require more detailed analysis. |
| const auto *GVar = cast<GlobalVariable>(GO); |
| |
| // Handle thread-local data first. |
| if (GVar->isThreadLocal()) { |
| if (isSuitableForBSS(GVar) && !TM.Options.NoZerosInBSS) { |
| // Zero-initialized TLS variables with local linkage always get classified |
| // as ThreadBSSLocal. |
| if (GVar->hasLocalLinkage()) { |
| return SectionKind::getThreadBSSLocal(); |
| } |
| return SectionKind::getThreadBSS(); |
| } |
| return SectionKind::getThreadData(); |
| } |
| |
| // Variables with common linkage always get classified as common. |
| if (GVar->hasCommonLinkage()) |
| return SectionKind::getCommon(); |
| |
| // Most non-mergeable zero data can be put in the BSS section unless otherwise |
| // specified. |
| if (isSuitableForBSS(GVar) && !TM.Options.NoZerosInBSS) { |
| if (GVar->hasLocalLinkage()) |
| return SectionKind::getBSSLocal(); |
| else if (GVar->hasExternalLinkage()) |
| return SectionKind::getBSSExtern(); |
| return SectionKind::getBSS(); |
| } |
| |
| // If the global is marked constant, we can put it into a mergable section, |
| // a mergable string section, or general .data if it contains relocations. |
| if (GVar->isConstant()) { |
| // If the initializer for the global contains something that requires a |
| // relocation, then we may have to drop this into a writable data section |
| // even though it is marked const. |
| const Constant *C = GVar->getInitializer(); |
| if (!C->needsRelocation()) { |
| // If the global is required to have a unique address, it can't be put |
| // into a mergable section: just drop it into the general read-only |
| // section instead. |
| if (!GVar->hasGlobalUnnamedAddr()) |
| return SectionKind::getReadOnly(); |
| |
| // If initializer is a null-terminated string, put it in a "cstring" |
| // section of the right width. |
| if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) { |
| if (IntegerType *ITy = |
| dyn_cast<IntegerType>(ATy->getElementType())) { |
| if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 || |
| ITy->getBitWidth() == 32) && |
| IsNullTerminatedString(C)) { |
| if (ITy->getBitWidth() == 8) |
| return SectionKind::getMergeable1ByteCString(); |
| if (ITy->getBitWidth() == 16) |
| return SectionKind::getMergeable2ByteCString(); |
| |
| assert(ITy->getBitWidth() == 32 && "Unknown width"); |
| return SectionKind::getMergeable4ByteCString(); |
| } |
| } |
| } |
| |
| // Otherwise, just drop it into a mergable constant section. If we have |
| // a section for this size, use it, otherwise use the arbitrary sized |
| // mergable section. |
| switch ( |
| GVar->getParent()->getDataLayout().getTypeAllocSize(C->getType())) { |
| case 4: return SectionKind::getMergeableConst4(); |
| case 8: return SectionKind::getMergeableConst8(); |
| case 16: return SectionKind::getMergeableConst16(); |
| case 32: return SectionKind::getMergeableConst32(); |
| default: |
| return SectionKind::getReadOnly(); |
| } |
| |
| } else { |
| // In static, ROPI and RWPI relocation models, the linker will resolve |
| // all addresses, so the relocation entries will actually be constants by |
| // the time the app starts up. However, we can't put this into a |
| // mergable section, because the linker doesn't take relocations into |
| // consideration when it tries to merge entries in the section. |
| Reloc::Model ReloModel = TM.getRelocationModel(); |
| if (ReloModel == Reloc::Static || ReloModel == Reloc::ROPI || |
| ReloModel == Reloc::RWPI || ReloModel == Reloc::ROPI_RWPI || |
| !C->needsDynamicRelocation()) |
| return SectionKind::getReadOnly(); |
| |
| // Otherwise, the dynamic linker needs to fix it up, put it in the |
| // writable data.rel section. |
| return SectionKind::getReadOnlyWithRel(); |
| } |
| } |
| |
| // Okay, this isn't a constant. |
| return SectionKind::getData(); |
| } |
| |
| /// This method computes the appropriate section to emit the specified global |
| /// variable or function definition. This should not be passed external (or |
| /// available externally) globals. |
| MCSection *TargetLoweringObjectFile::SectionForGlobal( |
| const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const { |
| // Select section name. |
| if (GO->hasSection()) |
| return getExplicitSectionGlobal(GO, Kind, TM); |
| |
| if (auto *GVar = dyn_cast<GlobalVariable>(GO)) { |
| auto Attrs = GVar->getAttributes(); |
| if ((Attrs.hasAttribute("bss-section") && Kind.isBSS()) || |
| (Attrs.hasAttribute("data-section") && Kind.isData()) || |
| (Attrs.hasAttribute("relro-section") && Kind.isReadOnlyWithRel()) || |
| (Attrs.hasAttribute("rodata-section") && Kind.isReadOnly())) { |
| return getExplicitSectionGlobal(GO, Kind, TM); |
| } |
| } |
| |
| if (auto *F = dyn_cast<Function>(GO)) { |
| if (F->hasFnAttribute("implicit-section-name")) |
| return getExplicitSectionGlobal(GO, Kind, TM); |
| } |
| |
| // Use default section depending on the 'type' of global |
| return SelectSectionForGlobal(GO, Kind, TM); |
| } |
| |
| /// This method computes the appropriate section to emit the specified global |
| /// variable or function definition. This should not be passed external (or |
| /// available externally) globals. |
| MCSection * |
| TargetLoweringObjectFile::SectionForGlobal(const GlobalObject *GO, |
| const TargetMachine &TM) const { |
| return SectionForGlobal(GO, getKindForGlobal(GO, TM), TM); |
| } |
| |
| MCSection *TargetLoweringObjectFile::getSectionForJumpTable( |
| const Function &F, const TargetMachine &TM) const { |
| Align Alignment(1); |
| return getSectionForConstant(F.getParent()->getDataLayout(), |
| SectionKind::getReadOnly(), /*C=*/nullptr, |
| Alignment); |
| } |
| |
| bool TargetLoweringObjectFile::shouldPutJumpTableInFunctionSection( |
| bool UsesLabelDifference, const Function &F) const { |
| // In PIC mode, we need to emit the jump table to the same section as the |
| // function body itself, otherwise the label differences won't make sense. |
| // FIXME: Need a better predicate for this: what about custom entries? |
| if (UsesLabelDifference) |
| return true; |
| |
| // We should also do if the section name is NULL or function is declared |
| // in discardable section |
| // FIXME: this isn't the right predicate, should be based on the MCSection |
| // for the function. |
| return F.isWeakForLinker(); |
| } |
| |
| /// Given a mergable constant with the specified size and relocation |
| /// information, return a section that it should be placed in. |
| MCSection *TargetLoweringObjectFile::getSectionForConstant( |
| const DataLayout &DL, SectionKind Kind, const Constant *C, |
| Align &Alignment) const { |
| if (Kind.isReadOnly() && ReadOnlySection != nullptr) |
| return ReadOnlySection; |
| |
| return DataSection; |
| } |
| |
| MCSection *TargetLoweringObjectFile::getSectionForMachineBasicBlock( |
| const Function &F, const MachineBasicBlock &MBB, |
| const TargetMachine &TM) const { |
| return nullptr; |
| } |
| |
| MCSection *TargetLoweringObjectFile::getUniqueSectionForFunction( |
| const Function &F, const TargetMachine &TM) const { |
| return nullptr; |
| } |
| |
| /// getTTypeGlobalReference - Return an MCExpr to use for a |
| /// reference to the specified global variable from exception |
| /// handling information. |
| const MCExpr *TargetLoweringObjectFile::getTTypeGlobalReference( |
| const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM, |
| MachineModuleInfo *MMI, MCStreamer &Streamer) const { |
| const MCSymbolRefExpr *Ref = |
| MCSymbolRefExpr::create(TM.getSymbol(GV), getContext()); |
| |
| return getTTypeReference(Ref, Encoding, Streamer); |
| } |
| |
| const MCExpr *TargetLoweringObjectFile:: |
| getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding, |
| MCStreamer &Streamer) const { |
| switch (Encoding & 0x70) { |
| default: |
| report_fatal_error("We do not support this DWARF encoding yet!"); |
| case dwarf::DW_EH_PE_absptr: |
| // Do nothing special |
| return Sym; |
| case dwarf::DW_EH_PE_pcrel: { |
| // Emit a label to the streamer for the current position. This gives us |
| // .-foo addressing. |
| MCSymbol *PCSym = getContext().createTempSymbol(); |
| Streamer.emitLabel(PCSym); |
| const MCExpr *PC = MCSymbolRefExpr::create(PCSym, getContext()); |
| return MCBinaryExpr::createSub(Sym, PC, getContext()); |
| } |
| } |
| } |
| |
| const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const { |
| // FIXME: It's not clear what, if any, default this should have - perhaps a |
| // null return could mean 'no location' & we should just do that here. |
| return MCSymbolRefExpr::create(Sym, getContext()); |
| } |
| |
| void TargetLoweringObjectFile::getNameWithPrefix( |
| SmallVectorImpl<char> &OutName, const GlobalValue *GV, |
| const TargetMachine &TM) const { |
| Mang->getNameWithPrefix(OutName, GV, /*CannotUsePrivateLabel=*/false); |
| } |