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llvm-project/llvm/lib/Target/TargetLoweringObjectFile.cpp

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//===-- llvm/Target/TargetLoweringObjectFile.cpp - Object File Info -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements classes used to handle lowerings specific to common
// object file formats.
//
//===----------------------------------------------------------------------===//
#include "llvm/Target/TargetLoweringObjectFile.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/GlobalVariable.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Target/Mangler.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Dwarf.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/SmallString.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) {
Ctx = &ctx;
InitMCObjectFileInfo(TM.getTargetTriple(),
TM.getRelocationModel(), TM.getCodeModel(), *Ctx);
}
TargetLoweringObjectFile::~TargetLoweringObjectFile() {
}
static bool isSuitableForBSS(const GlobalVariable *GV, bool NoZerosInBSS) {
const Constant *C = GV->getInitializer();
// Must have zero initializer.
if (!C->isNullValue())
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->getSection().empty())
return false;
// If -nozero-initialized-in-bss is specified, don't ever use BSS.
if (NoZerosInBSS)
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 ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
ArrayType *ATy = cast<ArrayType>(C->getType());
if (ATy->getNumElements() == 0) return false;
ConstantInt *Null =
dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
if (Null == 0 || !Null->isZero())
return false; // Not null terminated.
// Verify that the null doesn't occur anywhere else in the string.
for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i)
// Reject constantexpr elements etc.
if (!isa<ConstantInt>(CVA->getOperand(i)) ||
CVA->getOperand(i) == Null)
return false;
return true;
}
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::
getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
MachineModuleInfo *MMI) const {
return Mang->getSymbol(GV);
}
void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
const TargetMachine &TM,
const MCSymbol *Sym) const {
}
/// getKindForGlobal - This is a top-level target-independent classifier for
/// a global variable. Given an global variable and information from TM, it
/// classifies the global in a variety of ways that make various target
/// implementations simpler. The target implementation is free to ignore this
/// extra info of course.
SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
const TargetMachine &TM){
assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
"Can only be used for global definitions");
Reloc::Model ReloModel = TM.getRelocationModel();
// Early exit - functions should be always in text sections.
const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
if (GVar == 0)
return SectionKind::getText();
// 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();
// Variable can be easily put to BSS section.
if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
if (GVar->hasLocalLinkage())
return SectionKind::getBSSLocal();
else if (GVar->hasExternalLinkage())
return SectionKind::getBSSExtern();
return SectionKind::getBSS();
}
const Constant *C = GVar->getInitializer();
// 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 wriable data section
// even though it is marked const.
switch (C->getRelocationInfo()) {
case Constant::NoRelocation:
// 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->hasUnnamedAddr())
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 (TM.getTargetData()->getTypeAllocSize(C->getType())) {
case 4: return SectionKind::getMergeableConst4();
case 8: return SectionKind::getMergeableConst8();
case 16: return SectionKind::getMergeableConst16();
default: return SectionKind::getMergeableConst();
}
case Constant::LocalRelocation:
// In static relocation model, 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.
if (ReloModel == Reloc::Static)
return SectionKind::getReadOnly();
// Otherwise, the dynamic linker needs to fix it up, put it in the
// writable data.rel.local section.
return SectionKind::getReadOnlyWithRelLocal();
case Constant::GlobalRelocations:
// In static relocation model, 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.
if (ReloModel == Reloc::Static)
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. If the initializer for the global is going
// to require a runtime relocation by the dynamic linker, put it into a more
// specific section to improve startup time of the app. This coalesces these
// globals together onto fewer pages, improving the locality of the dynamic
// linker.
if (ReloModel == Reloc::Static)
return SectionKind::getDataNoRel();
switch (C->getRelocationInfo()) {
case Constant::NoRelocation:
return SectionKind::getDataNoRel();
case Constant::LocalRelocation:
return SectionKind::getDataRelLocal();
case Constant::GlobalRelocations:
return SectionKind::getDataRel();
}
llvm_unreachable("Invalid relocation");
}
/// SectionForGlobal - 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.
const MCSection *TargetLoweringObjectFile::
SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
const TargetMachine &TM) const {
// Select section name.
if (GV->hasSection())
return getExplicitSectionGlobal(GV, Kind, Mang, TM);
// Use default section depending on the 'type' of global
return SelectSectionForGlobal(GV, Kind, Mang, TM);
}
// Lame default implementation. Calculate the section name for global.
const MCSection *
TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
SectionKind Kind,
Mangler *Mang,
const TargetMachine &TM) const{
assert(!Kind.isThreadLocal() && "Doesn't support TLS");
if (Kind.isText())
return getTextSection();
if (Kind.isBSS() && BSSSection != 0)
return BSSSection;
if (Kind.isReadOnly() && ReadOnlySection != 0)
return ReadOnlySection;
return getDataSection();
}
/// getSectionForConstant - Given a mergable constant with the
/// specified size and relocation information, return a section that it
/// should be placed in.
const MCSection *
TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
if (Kind.isReadOnly() && ReadOnlySection != 0)
return ReadOnlySection;
return DataSection;
}
/// getExprForDwarfGlobalReference - Return an MCExpr to use for a
/// reference to the specified global variable from exception
/// handling information.
const MCExpr *TargetLoweringObjectFile::
getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
MachineModuleInfo *MMI, unsigned Encoding,
MCStreamer &Streamer) const {
const MCSymbol *Sym = Mang->getSymbol(GV);
return getExprForDwarfReference(Sym, Encoding, Streamer);
}
const MCExpr *TargetLoweringObjectFile::
getExprForDwarfReference(const MCSymbol *Sym, unsigned Encoding,
MCStreamer &Streamer) const {
const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
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 Res;
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(Res, PC, getContext());
}
}
}
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