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+//===-- 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(TM.getTargetTriple(), TM.isPositionIndependent(), ctx,
+ 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)
+ 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)
+ 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;
+}
+
+/// 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);
+}