326 lines
12 KiB
C++
326 lines
12 KiB
C++
//===-- llvm/Target/TargetLoweringObjectFile.cpp - Object File Info -------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements classes used to handle lowerings specific to common
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// object file formats.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Target/TargetLoweringObjectFile.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCExpr.h"
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#include "llvm/MC/MCStreamer.h"
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#include "llvm/MC/MCSymbol.h"
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#include "llvm/Target/Mangler.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetOptions.h"
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#include "llvm/Support/Dwarf.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/ADT/SmallString.h"
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using namespace llvm;
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//===----------------------------------------------------------------------===//
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// Generic Code
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//===----------------------------------------------------------------------===//
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/// Initialize - this method must be called before any actual lowering is
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/// done. This specifies the current context for codegen, and gives the
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/// lowering implementations a chance to set up their default sections.
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void TargetLoweringObjectFile::Initialize(MCContext &ctx,
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const TargetMachine &TM) {
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Ctx = &ctx;
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InitMCObjectFileInfo(TM.getTargetTriple(),
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TM.getRelocationModel(), TM.getCodeModel(), *Ctx);
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}
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TargetLoweringObjectFile::~TargetLoweringObjectFile() {
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}
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static bool isSuitableForBSS(const GlobalVariable *GV) {
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const Constant *C = GV->getInitializer();
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// Must have zero initializer.
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if (!C->isNullValue())
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return false;
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// Leave constant zeros in readonly constant sections, so they can be shared.
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if (GV->isConstant())
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return false;
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// If the global has an explicit section specified, don't put it in BSS.
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if (!GV->getSection().empty())
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return false;
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// If -nozero-initialized-in-bss is specified, don't ever use BSS.
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if (NoZerosInBSS)
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return false;
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// Otherwise, put it in BSS!
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return true;
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}
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/// IsNullTerminatedString - Return true if the specified constant (which is
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/// known to have a type that is an array of 1/2/4 byte elements) ends with a
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/// nul value and contains no other nuls in it.
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static bool IsNullTerminatedString(const Constant *C) {
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ArrayType *ATy = cast<ArrayType>(C->getType());
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// First check: is we have constant array of i8 terminated with zero
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if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
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if (ATy->getNumElements() == 0) return false;
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ConstantInt *Null =
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dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
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if (Null == 0 || !Null->isZero())
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return false; // Not null terminated.
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// Verify that the null doesn't occur anywhere else in the string.
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for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i)
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// Reject constantexpr elements etc.
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if (!isa<ConstantInt>(CVA->getOperand(i)) ||
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CVA->getOperand(i) == Null)
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return false;
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return true;
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}
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// Another possibility: [1 x i8] zeroinitializer
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if (isa<ConstantAggregateZero>(C))
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return ATy->getNumElements() == 1;
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return false;
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}
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MCSymbol *TargetLoweringObjectFile::
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getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
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MachineModuleInfo *MMI) const {
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return Mang->getSymbol(GV);
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}
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void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
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const TargetMachine &TM,
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const MCSymbol *Sym) const {
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}
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/// getKindForGlobal - This is a top-level target-independent classifier for
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/// a global variable. Given an global variable and information from TM, it
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/// classifies the global in a variety of ways that make various target
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/// implementations simpler. The target implementation is free to ignore this
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/// extra info of course.
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SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
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const TargetMachine &TM){
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assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
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"Can only be used for global definitions");
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Reloc::Model ReloModel = TM.getRelocationModel();
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// Early exit - functions should be always in text sections.
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const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
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if (GVar == 0)
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return SectionKind::getText();
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// Handle thread-local data first.
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if (GVar->isThreadLocal()) {
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if (isSuitableForBSS(GVar))
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return SectionKind::getThreadBSS();
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return SectionKind::getThreadData();
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}
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// Variables with common linkage always get classified as common.
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if (GVar->hasCommonLinkage())
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return SectionKind::getCommon();
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// Variable can be easily put to BSS section.
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if (isSuitableForBSS(GVar)) {
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if (GVar->hasLocalLinkage())
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return SectionKind::getBSSLocal();
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else if (GVar->hasExternalLinkage())
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return SectionKind::getBSSExtern();
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return SectionKind::getBSS();
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}
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const Constant *C = GVar->getInitializer();
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// If the global is marked constant, we can put it into a mergable section,
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// a mergable string section, or general .data if it contains relocations.
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if (GVar->isConstant()) {
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// If the initializer for the global contains something that requires a
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// relocation, then we may have to drop this into a wriable data section
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// even though it is marked const.
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switch (C->getRelocationInfo()) {
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default: assert(0 && "unknown relocation info kind");
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case Constant::NoRelocation:
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// If the global is required to have a unique address, it can't be put
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// into a mergable section: just drop it into the general read-only
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// section instead.
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if (!GVar->hasUnnamedAddr())
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return SectionKind::getReadOnly();
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// If initializer is a null-terminated string, put it in a "cstring"
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// section of the right width.
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if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
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if (IntegerType *ITy =
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dyn_cast<IntegerType>(ATy->getElementType())) {
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if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
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ITy->getBitWidth() == 32) &&
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IsNullTerminatedString(C)) {
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if (ITy->getBitWidth() == 8)
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return SectionKind::getMergeable1ByteCString();
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if (ITy->getBitWidth() == 16)
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return SectionKind::getMergeable2ByteCString();
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assert(ITy->getBitWidth() == 32 && "Unknown width");
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return SectionKind::getMergeable4ByteCString();
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}
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}
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}
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// Otherwise, just drop it into a mergable constant section. If we have
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// a section for this size, use it, otherwise use the arbitrary sized
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// mergable section.
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switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
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case 4: return SectionKind::getMergeableConst4();
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case 8: return SectionKind::getMergeableConst8();
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case 16: return SectionKind::getMergeableConst16();
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default: return SectionKind::getMergeableConst();
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}
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case Constant::LocalRelocation:
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// In static relocation model, the linker will resolve all addresses, so
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// the relocation entries will actually be constants by the time the app
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// starts up. However, we can't put this into a mergable section, because
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// the linker doesn't take relocations into consideration when it tries to
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// merge entries in the section.
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if (ReloModel == Reloc::Static)
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return SectionKind::getReadOnly();
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// Otherwise, the dynamic linker needs to fix it up, put it in the
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// writable data.rel.local section.
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return SectionKind::getReadOnlyWithRelLocal();
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case Constant::GlobalRelocations:
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// In static relocation model, the linker will resolve all addresses, so
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// the relocation entries will actually be constants by the time the app
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// starts up. However, we can't put this into a mergable section, because
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// the linker doesn't take relocations into consideration when it tries to
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// merge entries in the section.
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if (ReloModel == Reloc::Static)
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return SectionKind::getReadOnly();
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// Otherwise, the dynamic linker needs to fix it up, put it in the
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// writable data.rel section.
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return SectionKind::getReadOnlyWithRel();
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}
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}
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// Okay, this isn't a constant. If the initializer for the global is going
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// to require a runtime relocation by the dynamic linker, put it into a more
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// specific section to improve startup time of the app. This coalesces these
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// globals together onto fewer pages, improving the locality of the dynamic
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// linker.
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if (ReloModel == Reloc::Static)
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return SectionKind::getDataNoRel();
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switch (C->getRelocationInfo()) {
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default: assert(0 && "unknown relocation info kind");
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case Constant::NoRelocation:
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return SectionKind::getDataNoRel();
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case Constant::LocalRelocation:
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return SectionKind::getDataRelLocal();
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case Constant::GlobalRelocations:
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return SectionKind::getDataRel();
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}
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}
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/// SectionForGlobal - This method computes the appropriate section to emit
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/// the specified global variable or function definition. This should not
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/// be passed external (or available externally) globals.
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const MCSection *TargetLoweringObjectFile::
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SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
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const TargetMachine &TM) const {
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// Select section name.
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if (GV->hasSection())
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return getExplicitSectionGlobal(GV, Kind, Mang, TM);
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// Use default section depending on the 'type' of global
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return SelectSectionForGlobal(GV, Kind, Mang, TM);
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}
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// Lame default implementation. Calculate the section name for global.
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const MCSection *
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TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
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SectionKind Kind,
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Mangler *Mang,
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const TargetMachine &TM) const{
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assert(!Kind.isThreadLocal() && "Doesn't support TLS");
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if (Kind.isText())
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return getTextSection();
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if (Kind.isBSS() && BSSSection != 0)
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return BSSSection;
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if (Kind.isReadOnly() && ReadOnlySection != 0)
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return ReadOnlySection;
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return getDataSection();
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}
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/// getSectionForConstant - Given a mergable constant with the
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/// specified size and relocation information, return a section that it
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/// should be placed in.
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const MCSection *
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TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
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if (Kind.isReadOnly() && ReadOnlySection != 0)
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return ReadOnlySection;
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return DataSection;
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}
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/// getExprForDwarfGlobalReference - Return an MCExpr to use for a
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/// reference to the specified global variable from exception
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/// handling information.
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const MCExpr *TargetLoweringObjectFile::
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getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
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MachineModuleInfo *MMI, unsigned Encoding,
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MCStreamer &Streamer) const {
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const MCSymbol *Sym = Mang->getSymbol(GV);
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return getExprForDwarfReference(Sym, Encoding, Streamer);
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}
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const MCExpr *TargetLoweringObjectFile::
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getExprForDwarfReference(const MCSymbol *Sym, unsigned Encoding,
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MCStreamer &Streamer) const {
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const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
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switch (Encoding & 0x70) {
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default:
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report_fatal_error("We do not support this DWARF encoding yet!");
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case dwarf::DW_EH_PE_absptr:
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// Do nothing special
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return Res;
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case dwarf::DW_EH_PE_pcrel: {
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// Emit a label to the streamer for the current position. This gives us
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// .-foo addressing.
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MCSymbol *PCSym = getContext().CreateTempSymbol();
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Streamer.EmitLabel(PCSym);
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const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
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return MCBinaryExpr::CreateSub(Res, PC, getContext());
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}
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}
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}
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