llvm-mirror/lib/Target/TargetLoweringObjectFile.cpp
Bill Wendling 7a13f3bde3 Remove a flag that would set the ".eh" symbol as .globl. MachO was the only one
who used this flag, and it now emits CFI and doesn't emit this anymore. All
other targets left this flag "false".
<rdar://problem/8486371>

llvm-svn: 130918
2011-05-05 06:49:15 +00:00

360 lines
13 KiB
C++

//===-- 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
//===----------------------------------------------------------------------===//
TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
TextSection = 0;
DataSection = 0;
BSSSection = 0;
ReadOnlySection = 0;
StaticCtorSection = 0;
StaticDtorSection = 0;
LSDASection = 0;
CommDirectiveSupportsAlignment = true;
DwarfAbbrevSection = 0;
DwarfInfoSection = 0;
DwarfLineSection = 0;
DwarfFrameSection = 0;
DwarfPubNamesSection = 0;
DwarfPubTypesSection = 0;
DwarfDebugInlineSection = 0;
DwarfStrSection = 0;
DwarfLocSection = 0;
DwarfARangesSection = 0;
DwarfRangesSection = 0;
DwarfMacroInfoSection = 0;
IsFunctionEHFrameSymbolPrivate = true;
SupportsWeakOmittedEHFrame = true;
}
TargetLoweringObjectFile::~TargetLoweringObjectFile() {
}
static bool isSuitableForBSS(const GlobalVariable *GV) {
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.
static bool IsNullTerminatedString(const Constant *C) {
const ArrayType *ATy = cast<ArrayType>(C->getType());
// First check: is we have constant array of i8 terminated with zero
if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
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;
}
// Another possibility: [1 x i8] zeroinitializer
if (isa<ConstantAggregateZero>(C))
return ATy->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))
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)) {
if (GVar->hasLocalLinkage())
return SectionKind::getBSSLocal();
else if (GVar->hasExternalLinkage())
return SectionKind::getBSSExtern();
return SectionKind::getBSS();
}
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()) {
default: assert(0 && "unknown relocation info kind");
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 (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
if (const 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()) {
default: assert(0 && "unknown relocation info kind");
case Constant::NoRelocation:
return SectionKind::getDataNoRel();
case Constant::LocalRelocation:
return SectionKind::getDataRelLocal();
case Constant::GlobalRelocations:
return SectionKind::getDataRel();
}
}
/// 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());
}
}
}
unsigned TargetLoweringObjectFile::getPersonalityEncoding() const {
return dwarf::DW_EH_PE_absptr;
}
unsigned TargetLoweringObjectFile::getLSDAEncoding() const {
return dwarf::DW_EH_PE_absptr;
}
unsigned TargetLoweringObjectFile::getFDEEncoding(bool CFI) const {
return dwarf::DW_EH_PE_absptr;
}
unsigned TargetLoweringObjectFile::getTTypeEncoding() const {
return dwarf::DW_EH_PE_absptr;
}