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llvm-project/llvm/lib/MC/MCELFStreamer.cpp

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//===- lib/MC/MCELFStreamer.cpp - ELF Object Output ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file assembles .s files and emits ELF .o object files.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCELFStreamer.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELF.h"
#include "llvm/MC/MCELFSymbolFlags.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
inline void MCELFStreamer::SetSection(StringRef Section, unsigned Type,
unsigned Flags, SectionKind Kind) {
SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
}
inline void MCELFStreamer::SetSectionData() {
SetSection(".data",
ELF::SHT_PROGBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC,
SectionKind::getDataRel());
EmitCodeAlignment(4, 0);
}
inline void MCELFStreamer::SetSectionText() {
SetSection(".text",
ELF::SHT_PROGBITS,
ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
SectionKind::getText());
EmitCodeAlignment(4, 0);
}
inline void MCELFStreamer::SetSectionBss() {
SetSection(".bss",
ELF::SHT_NOBITS,
ELF::SHF_WRITE | ELF::SHF_ALLOC,
SectionKind::getBSS());
EmitCodeAlignment(4, 0);
}
MCELFStreamer::~MCELFStreamer() {
}
void MCELFStreamer::InitToTextSection() {
SetSectionText();
}
void MCELFStreamer::InitSections() {
// This emulates the same behavior of GNU as. This makes it easier
// to compare the output as the major sections are in the same order.
SetSectionText();
SetSectionData();
SetSectionBss();
SetSectionText();
}
void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
MCObjectStreamer::EmitLabel(Symbol);
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(Symbol->getSection());
MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
if (Section.getFlags() & ELF::SHF_TLS)
MCELF::SetType(SD, ELF::STT_TLS);
}
void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
EmitLabel(Symbol);
}
void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
switch (Flag) {
case MCAF_SyntaxUnified: return; // no-op here.
case MCAF_Code16: return; // Change parsing mode; no-op here.
case MCAF_Code32: return; // Change parsing mode; no-op here.
case MCAF_Code64: return; // Change parsing mode; no-op here.
case MCAF_SubsectionsViaSymbols:
getAssembler().setSubsectionsViaSymbols(true);
return;
}
llvm_unreachable("invalid assembler flag!");
}
void MCELFStreamer::ChangeSection(const MCSection *Section) {
MCSectionData *CurSection = getCurrentSectionData();
if (CurSection && CurSection->isBundleLocked())
report_fatal_error("Unterminated .bundle_lock when changing a section");
const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
if (Grp)
getAssembler().getOrCreateSymbolData(*Grp);
this->MCObjectStreamer::ChangeSection(Section);
}
void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
getAssembler().getOrCreateSymbolData(*Symbol);
MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
Alias->setVariableValue(Value);
}
void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
MCSymbolAttr Attribute) {
// Indirect symbols are handled differently, to match how 'as' handles
// them. This makes writing matching .o files easier.
if (Attribute == MCSA_IndirectSymbol) {
// Note that we intentionally cannot use the symbol data here; this is
// important for matching the string table that 'as' generates.
IndirectSymbolData ISD;
ISD.Symbol = Symbol;
ISD.SectionData = getCurrentSectionData();
getAssembler().getIndirectSymbols().push_back(ISD);
return;
}
// Adding a symbol attribute always introduces the symbol, note that an
// important side effect of calling getOrCreateSymbolData here is to register
// the symbol with the assembler.
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
// The implementation of symbol attributes is designed to match 'as', but it
// leaves much to desired. It doesn't really make sense to arbitrarily add and
// remove flags, but 'as' allows this (in particular, see .desc).
//
// In the future it might be worth trying to make these operations more well
// defined.
switch (Attribute) {
case MCSA_LazyReference:
case MCSA_Reference:
case MCSA_SymbolResolver:
case MCSA_PrivateExtern:
case MCSA_WeakDefinition:
case MCSA_WeakDefAutoPrivate:
case MCSA_Invalid:
case MCSA_IndirectSymbol:
llvm_unreachable("Invalid symbol attribute for ELF!");
case MCSA_NoDeadStrip:
case MCSA_ELF_TypeGnuUniqueObject:
// Ignore for now.
break;
case MCSA_Global:
MCELF::SetBinding(SD, ELF::STB_GLOBAL);
SD.setExternal(true);
BindingExplicitlySet.insert(Symbol);
break;
case MCSA_WeakReference:
case MCSA_Weak:
MCELF::SetBinding(SD, ELF::STB_WEAK);
SD.setExternal(true);
BindingExplicitlySet.insert(Symbol);
break;
case MCSA_Local:
MCELF::SetBinding(SD, ELF::STB_LOCAL);
SD.setExternal(false);
BindingExplicitlySet.insert(Symbol);
break;
case MCSA_ELF_TypeFunction:
MCELF::SetType(SD, ELF::STT_FUNC);
break;
case MCSA_ELF_TypeIndFunction:
MCELF::SetType(SD, ELF::STT_GNU_IFUNC);
break;
case MCSA_ELF_TypeObject:
MCELF::SetType(SD, ELF::STT_OBJECT);
break;
case MCSA_ELF_TypeTLS:
MCELF::SetType(SD, ELF::STT_TLS);
break;
case MCSA_ELF_TypeCommon:
MCELF::SetType(SD, ELF::STT_COMMON);
break;
case MCSA_ELF_TypeNoType:
MCELF::SetType(SD, ELF::STT_NOTYPE);
break;
case MCSA_Protected:
MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
break;
case MCSA_Hidden:
MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
break;
case MCSA_Internal:
MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
break;
}
}
void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
if (!BindingExplicitlySet.count(Symbol)) {
MCELF::SetBinding(SD, ELF::STB_GLOBAL);
SD.setExternal(true);
}
MCELF::SetType(SD, ELF::STT_OBJECT);
if (MCELF::GetBinding(SD) == ELF_STB_Local) {
const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
ELF::SHT_NOBITS,
ELF::SHF_WRITE |
ELF::SHF_ALLOC,
SectionKind::getBSS());
Symbol->setSection(*Section);
struct LocalCommon L = {&SD, Size, ByteAlignment};
LocalCommons.push_back(L);
} else {
SD.setCommon(Size, ByteAlignment);
}
SD.setSize(MCConstantExpr::Create(Size, getContext()));
}
void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
SD.setSize(Value);
}
void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
// FIXME: Should this be caught and done earlier?
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
MCELF::SetBinding(SD, ELF::STB_LOCAL);
SD.setExternal(false);
BindingExplicitlySet.insert(Symbol);
EmitCommonSymbol(Symbol, Size, ByteAlignment);
}
void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
unsigned AddrSpace) {
if (getCurrentSectionData()->isBundleLocked())
report_fatal_error("Emitting values inside a locked bundle is forbidden");
fixSymbolsInTLSFixups(Value);
MCObjectStreamer::EmitValueImpl(Value, Size, AddrSpace);
}
void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
int64_t Value,
unsigned ValueSize,
unsigned MaxBytesToEmit) {
if (getCurrentSectionData()->isBundleLocked())
report_fatal_error("Emitting values inside a locked bundle is forbidden");
MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
ValueSize, MaxBytesToEmit);
}
// Add a symbol for the file name of this module. This is the second
// entry in the module's symbol table (the first being the null symbol).
void MCELFStreamer::EmitFileDirective(StringRef Filename) {
MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
Symbol->setSection(*getCurrentSection());
Symbol->setAbsolute();
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
}
void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
switch (expr->getKind()) {
case MCExpr::Target:
cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
break;
case MCExpr::Constant:
break;
case MCExpr::Binary: {
const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
fixSymbolsInTLSFixups(be->getLHS());
fixSymbolsInTLSFixups(be->getRHS());
break;
}
case MCExpr::SymbolRef: {
const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
switch (symRef.getKind()) {
default:
return;
case MCSymbolRefExpr::VK_GOTTPOFF:
case MCSymbolRefExpr::VK_INDNTPOFF:
case MCSymbolRefExpr::VK_NTPOFF:
case MCSymbolRefExpr::VK_GOTNTPOFF:
case MCSymbolRefExpr::VK_TLSGD:
case MCSymbolRefExpr::VK_TLSLD:
case MCSymbolRefExpr::VK_TLSLDM:
case MCSymbolRefExpr::VK_TPOFF:
case MCSymbolRefExpr::VK_DTPOFF:
case MCSymbolRefExpr::VK_ARM_TLSGD:
case MCSymbolRefExpr::VK_ARM_TPOFF:
case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
case MCSymbolRefExpr::VK_Mips_TLSGD:
case MCSymbolRefExpr::VK_Mips_GOTTPREL:
case MCSymbolRefExpr::VK_Mips_TPREL_HI:
case MCSymbolRefExpr::VK_Mips_TPREL_LO:
break;
}
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
MCELF::SetType(SD, ELF::STT_TLS);
break;
}
case MCExpr::Unary:
fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
break;
}
}
void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
this->MCObjectStreamer::EmitInstToFragment(Inst);
MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
}
void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
MCAssembler &Assembler = getAssembler();
SmallVector<MCFixup, 4> Fixups;
SmallString<256> Code;
raw_svector_ostream VecOS(Code);
Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
VecOS.flush();
for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
fixSymbolsInTLSFixups(Fixups[i].getValue());
// There are several possibilities here:
//
// If bundling is disabled, append the encoded instruction to the current data
// fragment (or create a new such fragment if the current fragment is not a
// data fragment).
//
// If bundling is enabled:
// - If we're not in a bundle-locked group, emit the instruction into a
// fragment of its own. If there are no fixups registered for the
// instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
// MCDataFragment.
// - If we're in a bundle-locked group, append the instruction to the current
// data fragment because we want all the instructions in a group to get into
// the same fragment. Be careful not to do that for the first instruction in
// the group, though.
MCDataFragment *DF;
if (Assembler.isBundlingEnabled()) {
MCSectionData *SD = getCurrentSectionData();
if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
// If we are bundle-locked, we re-use the current fragment.
// The bundle-locking directive ensures this is a new data fragment.
DF = cast<MCDataFragment>(getCurrentFragment());
else if (!SD->isBundleLocked() && Fixups.size() == 0) {
// Optimize memory usage by emitting the instruction to a
// MCCompactEncodedInstFragment when not in a bundle-locked group and
// there are no fixups registered.
MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment(SD);
CEIF->getContents().append(Code.begin(), Code.end());
return;
} else {
DF = new MCDataFragment(SD);
if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
// If this is a new fragment created for a bundle-locked group, and the
// group was marked as "align_to_end", set a flag in the fragment.
DF->setAlignToBundleEnd(true);
}
}
// We're now emitting an instruction in a bundle group, so this flag has
// to be turned off.
SD->setBundleGroupBeforeFirstInst(false);
} else {
DF = getOrCreateDataFragment();
}
// Add the fixups and data.
for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
DF->getFixups().push_back(Fixups[i]);
}
DF->setHasInstructions(true);
DF->getContents().append(Code.begin(), Code.end());
}
void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
assert(AlignPow2 <= 30 && "Invalid bundle alignment");
MCAssembler &Assembler = getAssembler();
if (Assembler.getBundleAlignSize() == 0 && AlignPow2 > 0)
Assembler.setBundleAlignSize(1 << AlignPow2);
else
report_fatal_error(".bundle_align_mode should be only set once per file");
}
void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
MCSectionData *SD = getCurrentSectionData();
// Sanity checks
//
if (!getAssembler().isBundlingEnabled())
report_fatal_error(".bundle_lock forbidden when bundling is disabled");
else if (SD->isBundleLocked())
report_fatal_error("Nesting of .bundle_lock is forbidden");
SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
MCSectionData::BundleLocked);
SD->setBundleGroupBeforeFirstInst(true);
}
void MCELFStreamer::EmitBundleUnlock() {
MCSectionData *SD = getCurrentSectionData();
// Sanity checks
if (!getAssembler().isBundlingEnabled())
report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
else if (!SD->isBundleLocked())
report_fatal_error(".bundle_unlock without matching lock");
else if (SD->isBundleGroupBeforeFirstInst())
report_fatal_error("Empty bundle-locked group is forbidden");
SD->setBundleLockState(MCSectionData::NotBundleLocked);
}
void MCELFStreamer::FinishImpl() {
EmitFrames(true);
for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
e = LocalCommons.end();
i != e; ++i) {
MCSymbolData *SD = i->SD;
uint64_t Size = i->Size;
unsigned ByteAlignment = i->ByteAlignment;
const MCSymbol &Symbol = SD->getSymbol();
const MCSection &Section = Symbol.getSection();
MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
SD->setFragment(F);
// Update the maximum alignment of the section if necessary.
if (ByteAlignment > SectData.getAlignment())
SectData.setAlignment(ByteAlignment);
}
this->MCObjectStreamer::FinishImpl();
}
void MCELFStreamer::EmitTCEntry(const MCSymbol &S) {
// Creates a R_PPC64_TOC relocation
MCObjectStreamer::EmitSymbolValue(&S, 8);
}
MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
raw_ostream &OS, MCCodeEmitter *CE,
bool RelaxAll, bool NoExecStack) {
MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
if (NoExecStack)
S->getAssembler().setNoExecStack(true);
return S;
}
void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
llvm_unreachable("Generic ELF doesn't support this directive");
}
void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
llvm_unreachable("ELF doesn't support this directive");
}
void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
llvm_unreachable("ELF doesn't support this directive");
}
void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
llvm_unreachable("ELF doesn't support this directive");
}
void MCELFStreamer::EmitCOFFSymbolType(int Type) {
llvm_unreachable("ELF doesn't support this directive");
}
void MCELFStreamer::EndCOFFSymbolDef() {
llvm_unreachable("ELF doesn't support this directive");
}
void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
uint64_t Size, unsigned ByteAlignment) {
llvm_unreachable("ELF doesn't support this directive");
}
void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
uint64_t Size, unsigned ByteAlignment) {
llvm_unreachable("ELF doesn't support this directive");
}
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