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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/GlobalVariable.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCSection.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Mangler.h"
#include "llvm/ADT/StringExtras.h"
using namespace llvm;
//===----------------------------------------------------------------------===//
// Generic Code
//===----------------------------------------------------------------------===//
TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
TextSection = 0;
DataSection = 0;
BSSSection = 0;
ReadOnlySection = 0;
}
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;
}
static bool isConstantString(const Constant *C) {
// First check: is we have constant array of i8 terminated with zero
const ConstantArray *CVA = dyn_cast<ConstantArray>(C);
// Check, if initializer is a null-terminated string
if (CVA && CVA->isCString())
return true;
// Another possibility: [1 x i8] zeroinitializer
if (isa<ConstantAggregateZero>(C))
if (const ArrayType *Ty = dyn_cast<ArrayType>(C->getType()))
return (Ty->getElementType() == Type::Int8Ty &&
Ty->getNumElements() == 1);
return false;
}
/// SectionKindForGlobal - 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.
static SectionKind SectionKindForGlobal(const GlobalValue *GV,
const TargetMachine &TM) {
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();
}
// Variable can be easily put to BSS section.
if (isSuitableForBSS(GVar))
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: llvm_unreachable("unknown relocation info kind");
case Constant::NoRelocation:
// If initializer is a null-terminated string, put it in a "cstring"
// section if the target has it.
if (isConstantString(C))
return SectionKind::getMergeableCString();
// 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: llvm_unreachable("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, Mangler *Mang,
const TargetMachine &TM) const {
assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
"Can only be used for global definitions");
SectionKind Kind = SectionKindForGlobal(GV, TM);
// Select section name.
if (GV->hasSection()) {
// If the target has special section hacks for specifically named globals,
// return them now.
if (const MCSection *TS = getSpecialCasedSectionGlobals(GV, Mang, Kind))
return TS;
// If the target has magic semantics for certain section names, make sure to
// pick up the flags. This allows the user to write things with attribute
// section and still get the appropriate section flags printed.
Kind = getKindForNamedSection(GV->getSection().c_str(), Kind);
return getOrCreateSection(GV->getSection().c_str(), false, Kind);
}
// 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;
}
const MCSection *TargetLoweringObjectFile::
getOrCreateSection(const char *Name, bool isDirective, SectionKind Kind) const {
if (MCSection *S = Ctx->GetSection(Name))
return S;
return MCSection::Create(Name, isDirective, Kind, *Ctx);
}
//===----------------------------------------------------------------------===//
// ELF
//===----------------------------------------------------------------------===//
void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
const TargetMachine &TM) {
TargetLoweringObjectFile::Initialize(Ctx, TM);
if (!HasCrazyBSS)
BSSSection = getOrCreateSection("\t.bss", true, SectionKind::getBSS());
else
// PPC/Linux doesn't support the .bss directive, it needs .section .bss.
// FIXME: Does .section .bss work everywhere??
// FIXME2: this should just be handle by the section printer. We should get
// away from syntactic view of the sections and MCSection should just be a
// semantic view.
BSSSection = getOrCreateSection("\t.bss", false, SectionKind::getBSS());
TextSection = getOrCreateSection("\t.text", true, SectionKind::getText());
DataSection = getOrCreateSection("\t.data", true, SectionKind::getDataRel());
ReadOnlySection =
getOrCreateSection("\t.rodata", false, SectionKind::getReadOnly());
TLSDataSection =
getOrCreateSection("\t.tdata", false, SectionKind::getThreadData());
CStringSection = getOrCreateSection("\t.rodata.str", true,
SectionKind::getMergeableCString());
TLSBSSSection = getOrCreateSection("\t.tbss", false,
SectionKind::getThreadBSS());
DataRelSection = getOrCreateSection("\t.data.rel", false,
SectionKind::getDataRel());
DataRelLocalSection = getOrCreateSection("\t.data.rel.local", false,
SectionKind::getDataRelLocal());
DataRelROSection = getOrCreateSection("\t.data.rel.ro", false,
SectionKind::getReadOnlyWithRel());
DataRelROLocalSection =
getOrCreateSection("\t.data.rel.ro.local", false,
SectionKind::getReadOnlyWithRelLocal());
MergeableConst4Section = getOrCreateSection(".rodata.cst4", false,
SectionKind::getMergeableConst4());
MergeableConst8Section = getOrCreateSection(".rodata.cst8", false,
SectionKind::getMergeableConst8());
MergeableConst16Section = getOrCreateSection(".rodata.cst16", false,
SectionKind::getMergeableConst16());
}
SectionKind TargetLoweringObjectFileELF::
getKindForNamedSection(const char *Name, SectionKind K) const {
if (Name[0] != '.') return K;
// Some lame default implementation based on some magic section names.
if (strncmp(Name, ".gnu.linkonce.b.", 16) == 0 ||
strncmp(Name, ".llvm.linkonce.b.", 17) == 0 ||
strncmp(Name, ".gnu.linkonce.sb.", 17) == 0 ||
strncmp(Name, ".llvm.linkonce.sb.", 18) == 0)
return SectionKind::getBSS();
if (strcmp(Name, ".tdata") == 0 ||
strncmp(Name, ".tdata.", 7) == 0 ||
strncmp(Name, ".gnu.linkonce.td.", 17) == 0 ||
strncmp(Name, ".llvm.linkonce.td.", 18) == 0)
return SectionKind::getThreadData();
if (strcmp(Name, ".tbss") == 0 ||
strncmp(Name, ".tbss.", 6) == 0 ||
strncmp(Name, ".gnu.linkonce.tb.", 17) == 0 ||
strncmp(Name, ".llvm.linkonce.tb.", 18) == 0)
return SectionKind::getThreadBSS();
return K;
}
void TargetLoweringObjectFileELF::
getSectionFlagsAsString(SectionKind Kind, SmallVectorImpl<char> &Str) const {
Str.push_back(',');
Str.push_back('"');
if (!Kind.isMetadata())
Str.push_back('a');
if (Kind.isText())
Str.push_back('x');
if (Kind.isWriteable())
Str.push_back('w');
if (Kind.isMergeableCString() ||
Kind.isMergeableConst4() ||
Kind.isMergeableConst8() ||
Kind.isMergeableConst16())
Str.push_back('M');
if (Kind.isMergeableCString())
Str.push_back('S');
if (Kind.isThreadLocal())
Str.push_back('T');
Str.push_back('"');
Str.push_back(',');
// If comment string is '@', e.g. as on ARM - use '%' instead
if (AtIsCommentChar)
Str.push_back('%');
else
Str.push_back('@');
const char *KindStr;
if (Kind.isBSS() || Kind.isThreadBSS())
KindStr = "nobits";
else
KindStr = "progbits";
Str.append(KindStr, KindStr+strlen(KindStr));
if (Kind.isMergeableCString()) {
// TODO: Eventually handle multiple byte character strings. For now, all
// mergable C strings are single byte.
Str.push_back(',');
Str.push_back('1');
} else if (Kind.isMergeableConst4()) {
Str.push_back(',');
Str.push_back('4');
} else if (Kind.isMergeableConst8()) {
Str.push_back(',');
Str.push_back('8');
} else if (Kind.isMergeableConst16()) {
Str.push_back(',');
Str.push_back('1');
Str.push_back('6');
}
}
static const char *getSectionPrefixForUniqueGlobal(SectionKind Kind) {
if (Kind.isText()) return ".gnu.linkonce.t.";
if (Kind.isReadOnly()) return ".gnu.linkonce.r.";
if (Kind.isThreadData()) return ".gnu.linkonce.td.";
if (Kind.isThreadBSS()) return ".gnu.linkonce.tb.";
if (Kind.isBSS()) return ".gnu.linkonce.b.";
if (Kind.isDataNoRel()) return ".gnu.linkonce.d.";
if (Kind.isDataRelLocal()) return ".gnu.linkonce.d.rel.local.";
if (Kind.isDataRel()) return ".gnu.linkonce.d.rel.";
if (Kind.isReadOnlyWithRelLocal()) return ".gnu.linkonce.d.rel.ro.local.";
assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
return ".gnu.linkonce.d.rel.ro.";
}
const MCSection *TargetLoweringObjectFileELF::
SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
Mangler *Mang, const TargetMachine &TM) const {
// If this global is linkonce/weak and the target handles this by emitting it
// into a 'uniqued' section name, create and return the section now.
if (GV->isWeakForLinker()) {
const char *Prefix = getSectionPrefixForUniqueGlobal(Kind);
std::string Name = Mang->makeNameProper(GV->getNameStr());
return getOrCreateSection((Prefix+Name).c_str(), false, Kind);
}
if (Kind.isText()) return TextSection;
if (Kind.isMergeableCString()) {
assert(CStringSection && "Should have string section prefix");
// We also need alignment here.
// FIXME: this is getting the alignment of the character, not the
// alignment of the global!
unsigned Align =
TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));
std::string Name = CStringSection->getName() + "1." + utostr(Align);
return getOrCreateSection(Name.c_str(), false,
SectionKind::getMergeableCString());
}
if (Kind.isMergeableConst()) {
if (Kind.isMergeableConst4())
return MergeableConst4Section;
if (Kind.isMergeableConst8())
return MergeableConst8Section;
if (Kind.isMergeableConst16())
return MergeableConst16Section;
return ReadOnlySection; // .const
}
if (Kind.isReadOnly()) return ReadOnlySection;
if (Kind.isThreadData()) return TLSDataSection;
if (Kind.isThreadBSS()) return TLSBSSSection;
if (Kind.isBSS()) return BSSSection;
if (Kind.isDataNoRel()) return DataSection;
if (Kind.isDataRelLocal()) return DataRelLocalSection;
if (Kind.isDataRel()) return DataRelSection;
if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
return DataRelROSection;
}
/// getSectionForConstant - Given a mergeable constant with the
/// specified size and relocation information, return a section that it
/// should be placed in.
const MCSection *TargetLoweringObjectFileELF::
getSectionForConstant(SectionKind Kind) const {
if (Kind.isMergeableConst4())
return MergeableConst4Section;
if (Kind.isMergeableConst8())
return MergeableConst8Section;
if (Kind.isMergeableConst16())
return MergeableConst16Section;
if (Kind.isReadOnly())
return ReadOnlySection;
if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
return DataRelROSection;
}
//===----------------------------------------------------------------------===//
// MachO
//===----------------------------------------------------------------------===//
void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
const TargetMachine &TM) {
TargetLoweringObjectFile::Initialize(Ctx, TM);
TextSection = getOrCreateSection("\t.text", true,
SectionKind::getText());
DataSection = getOrCreateSection("\t.data", true,
SectionKind::getDataRel());
CStringSection = getOrCreateSection("\t.cstring", true,
SectionKind::getMergeableCString());
FourByteConstantSection = getOrCreateSection("\t.literal4\n", true,
SectionKind::getMergeableConst4());
EightByteConstantSection = getOrCreateSection("\t.literal8\n", true,
SectionKind::getMergeableConst8());
// ld_classic doesn't support .literal16 in 32-bit mode, and ld64 falls back
// to using it in -static mode.
if (TM.getRelocationModel() != Reloc::Static &&
TM.getTargetData()->getPointerSize() == 32)
SixteenByteConstantSection =
getOrCreateSection("\t.literal16\n", true,
SectionKind::getMergeableConst16());
else
SixteenByteConstantSection = 0;
ReadOnlySection = getOrCreateSection("\t.const", true,
SectionKind::getReadOnly());
TextCoalSection =
getOrCreateSection("\t__TEXT,__textcoal_nt,coalesced,pure_instructions",
false, SectionKind::getText());
ConstTextCoalSection = getOrCreateSection("\t__TEXT,__const_coal,coalesced",
false,
SectionKind::getText());
ConstDataCoalSection = getOrCreateSection("\t__DATA,__const_coal,coalesced",
false,
SectionKind::getText());
ConstDataSection = getOrCreateSection("\t.const_data", true,
SectionKind::getReadOnlyWithRel());
DataCoalSection = getOrCreateSection("\t__DATA,__datacoal_nt,coalesced",
false,
SectionKind::getDataRel());
}
const MCSection *TargetLoweringObjectFileMachO::
SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
Mangler *Mang, const TargetMachine &TM) const {
assert(!Kind.isThreadLocal() && "Darwin doesn't support TLS");
if (Kind.isText())
return GV->isWeakForLinker() ? TextCoalSection : TextSection;
// If this is weak/linkonce, put this in a coalescable section, either in text
// or data depending on if it is writable.
if (GV->isWeakForLinker()) {
if (Kind.isReadOnly())
return ConstTextCoalSection;
return DataCoalSection;
}
// FIXME: Alignment check should be handled by section classifier.
if (Kind.isMergeableCString()) {
Constant *C = cast<GlobalVariable>(GV)->getInitializer();
const Type *Ty = cast<ArrayType>(C->getType())->getElementType();
const TargetData &TD = *TM.getTargetData();
unsigned Size = TD.getTypeAllocSize(Ty);
if (Size) {
unsigned Align = TD.getPreferredAlignment(cast<GlobalVariable>(GV));
if (Align <= 32)
return CStringSection;
}
return ReadOnlySection;
}
if (Kind.isMergeableConst()) {
if (Kind.isMergeableConst4())
return FourByteConstantSection;
if (Kind.isMergeableConst8())
return EightByteConstantSection;
if (Kind.isMergeableConst16() && SixteenByteConstantSection)
return SixteenByteConstantSection;
return ReadOnlySection; // .const
}
// FIXME: ROData -> const in -static mode that is relocatable but they happen
// by the static linker. Why not mergeable?
if (Kind.isReadOnly())
return ReadOnlySection;
// If this is marked const, put it into a const section. But if the dynamic
// linker needs to write to it, put it in the data segment.
if (Kind.isReadOnlyWithRel())
return ConstDataSection;
// Otherwise, just drop the variable in the normal data section.
return DataSection;
}
const MCSection *
TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind) const {
// If this constant requires a relocation, we have to put it in the data
// segment, not in the text segment.
if (Kind.isDataRel())
return ConstDataSection;
if (Kind.isMergeableConst4())
return FourByteConstantSection;
if (Kind.isMergeableConst8())
return EightByteConstantSection;
if (Kind.isMergeableConst16() && SixteenByteConstantSection)
return SixteenByteConstantSection;
return ReadOnlySection; // .const
}
/// shouldEmitUsedDirectiveFor - This hook allows targets to selectively decide
/// not to emit the UsedDirective for some symbols in llvm.used.
// FIXME: REMOVE this (rdar://7071300)
bool TargetLoweringObjectFileMachO::
shouldEmitUsedDirectiveFor(const GlobalValue *GV, Mangler *Mang) const {
/// On Darwin, internally linked data beginning with "L" or "l" does not have
/// the directive emitted (this occurs in ObjC metadata).
if (!GV) return false;
// Check whether the mangled name has the "Private" or "LinkerPrivate" prefix.
if (GV->hasLocalLinkage() && !isa<Function>(GV)) {
// FIXME: ObjC metadata is currently emitted as internal symbols that have
// \1L and \0l prefixes on them. Fix them to be Private/LinkerPrivate and
// this horrible hack can go away.
const std::string &Name = Mang->getMangledName(GV);
if (Name[0] == 'L' || Name[0] == 'l')
return false;
}
return true;
}
//===----------------------------------------------------------------------===//
// COFF
//===----------------------------------------------------------------------===//
void TargetLoweringObjectFileCOFF::Initialize(MCContext &Ctx,
const TargetMachine &TM) {
TargetLoweringObjectFile::Initialize(Ctx, TM);
TextSection = getOrCreateSection("\t.text", true,
SectionKind::getText());
DataSection = getOrCreateSection("\t.data", true,
SectionKind::getDataRel());
}
void TargetLoweringObjectFileCOFF::
getSectionFlagsAsString(SectionKind Kind, SmallVectorImpl<char> &Str) const {
// FIXME: Inefficient.
std::string Res = ",\"";
if (Kind.isText())
Res += 'x';
if (Kind.isWriteable())
Res += 'w';
Res += "\"";
Str.append(Res.begin(), Res.end());
}
static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
if (Kind.isText())
return ".text$linkonce";
if (Kind.isWriteable())
return ".data$linkonce";
return ".rdata$linkonce";
}
const MCSection *TargetLoweringObjectFileCOFF::
SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
Mangler *Mang, const TargetMachine &TM) const {
assert(!Kind.isThreadLocal() && "Doesn't support TLS");
// If this global is linkonce/weak and the target handles this by emitting it
// into a 'uniqued' section name, create and return the section now.
if (GV->isWeakForLinker()) {
const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
std::string Name = Mang->makeNameProper(GV->getNameStr());
return getOrCreateSection((Prefix+Name).c_str(), false, Kind);
}
if (Kind.isText())
return getTextSection();
return getDataSection();
}
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