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//===- MCMachOStreamer.cpp - MachO Streamer -------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDirectives.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCFragment.h"
#include "llvm/MC/MCLinkerOptimizationHint.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCSymbolMachO.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/SectionKind.h"
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <vector>
namespace llvm {
class MCInst;
class MCStreamer;
class MCSubtargetInfo;
class Triple;
} // namespace llvm
using namespace llvm;
namespace {
class MCMachOStreamer : public MCObjectStreamer {
private:
/// LabelSections - true if each section change should emit a linker local
/// label for use in relocations for assembler local references. Obviates the
/// need for local relocations. False by default.
bool LabelSections;
bool DWARFMustBeAtTheEnd;
bool CreatedADWARFSection;
/// HasSectionLabel - map of which sections have already had a non-local
/// label emitted to them. Used so we don't emit extraneous linker local
/// labels in the middle of the section.
DenseMap<const MCSection*, bool> HasSectionLabel;
void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &STI) override;
void emitDataRegion(DataRegionData::KindTy Kind);
void emitDataRegionEnd();
public:
MCMachOStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
std::unique_ptr<MCObjectWriter> OW,
std::unique_ptr<MCCodeEmitter> Emitter,
bool DWARFMustBeAtTheEnd, bool label)
: MCObjectStreamer(Context, std::move(MAB), std::move(OW),
std::move(Emitter)),
LabelSections(label), DWARFMustBeAtTheEnd(DWARFMustBeAtTheEnd),
CreatedADWARFSection(false) {}
/// state management
void reset() override {
CreatedADWARFSection = false;
HasSectionLabel.clear();
MCObjectStreamer::reset();
}
/// @name MCStreamer Interface
/// @{
void changeSection(MCSection *Sect, const MCExpr *Subsect) override;
void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
void emitAssignment(MCSymbol *Symbol, const MCExpr *Value) override;
void emitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol) override;
void emitAssemblerFlag(MCAssemblerFlag Flag) override;
void emitLinkerOptions(ArrayRef<std::string> Options) override;
void emitDataRegion(MCDataRegionType Kind) override;
void emitVersionMin(MCVersionMinType Kind, unsigned Major, unsigned Minor,
unsigned Update, VersionTuple SDKVersion) override;
void emitBuildVersion(unsigned Platform, unsigned Major, unsigned Minor,
unsigned Update, VersionTuple SDKVersion) override;
void emitDarwinTargetVariantBuildVersion(unsigned Platform, unsigned Major,
unsigned Minor, unsigned Update,
VersionTuple SDKVersion) override;
void emitThumbFunc(MCSymbol *Func) override;
bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
void emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
Align ByteAlignment) override;
void emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
Align ByteAlignment) override;
void emitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
uint64_t Size = 0, Align ByteAlignment = Align(1),
SMLoc Loc = SMLoc()) override;
void emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
Align ByteAlignment = Align(1)) override;
void emitIdent(StringRef IdentString) override {
llvm_unreachable("macho doesn't support this directive");
}
void emitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override {
getAssembler().getLOHContainer().addDirective(Kind, Args);
}
void emitCGProfileEntry(const MCSymbolRefExpr *From,
const MCSymbolRefExpr *To, uint64_t Count) override {
if (!From->getSymbol().isTemporary() && !To->getSymbol().isTemporary())
getAssembler().CGProfile.push_back({From, To, Count});
}
void finishImpl() override;
void finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE);
void finalizeCGProfile();
void createAddrSigSection();
};
} // end anonymous namespace.
static bool canGoAfterDWARF(const MCSectionMachO &MSec) {
// These sections are created by the assembler itself after the end of
// the .s file.
StringRef SegName = MSec.getSegmentName();
StringRef SecName = MSec.getName();
if (SegName == "__LD" && SecName == "__compact_unwind")
return true;
if (SegName == "__IMPORT") {
if (SecName == "__jump_table")
return true;
if (SecName == "__pointers")
return true;
}
if (SegName == "__TEXT" && SecName == "__eh_frame")
return true;
if (SegName == "__DATA" && (SecName == "__nl_symbol_ptr" ||
SecName == "__thread_ptr"))
return true;
if (SegName == "__LLVM" && SecName == "__cg_profile")
return true;
return false;
}
void MCMachOStreamer::changeSection(MCSection *Section,
const MCExpr *Subsection) {
// Change the section normally.
bool Created = changeSectionImpl(Section, Subsection);
const MCSectionMachO &MSec = *cast<MCSectionMachO>(Section);
StringRef SegName = MSec.getSegmentName();
if (SegName == "__DWARF")
CreatedADWARFSection = true;
else if (Created && DWARFMustBeAtTheEnd && !canGoAfterDWARF(MSec))
assert(!CreatedADWARFSection && "Creating regular section after DWARF");
// Output a linker-local symbol so we don't need section-relative local
// relocations. The linker hates us when we do that.
if (LabelSections && !HasSectionLabel[Section] &&
!Section->getBeginSymbol()) {
MCSymbol *Label = getContext().createLinkerPrivateTempSymbol();
Section->setBeginSymbol(Label);
HasSectionLabel[Section] = true;
}
}
void MCMachOStreamer::emitEHSymAttributes(const MCSymbol *Symbol,
MCSymbol *EHSymbol) {
getAssembler().registerSymbol(*Symbol);
if (Symbol->isExternal())
emitSymbolAttribute(EHSymbol, MCSA_Global);
if (cast<MCSymbolMachO>(Symbol)->isWeakDefinition())
emitSymbolAttribute(EHSymbol, MCSA_WeakDefinition);
if (Symbol->isPrivateExtern())
emitSymbolAttribute(EHSymbol, MCSA_PrivateExtern);
}
void MCMachOStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
// We have to create a new fragment if this is an atom defining symbol,
// fragments cannot span atoms.
if (getAssembler().isSymbolLinkerVisible(*Symbol))
insert(new MCDataFragment());
MCObjectStreamer::emitLabel(Symbol, Loc);
// This causes the reference type flag to be cleared. Darwin 'as' was "trying"
// to clear the weak reference and weak definition bits too, but the
// implementation was buggy. For now we just try to match 'as', for
// diffability.
//
// FIXME: Cleanup this code, these bits should be emitted based on semantic
// properties, not on the order of definition, etc.
cast<MCSymbolMachO>(Symbol)->clearReferenceType();
}
void MCMachOStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
MCValue Res;
if (Value->evaluateAsRelocatable(Res, nullptr, nullptr)) {
if (const MCSymbolRefExpr *SymAExpr = Res.getSymA()) {
const MCSymbol &SymA = SymAExpr->getSymbol();
if (!Res.getSymB() && (SymA.getName() == "" || Res.getConstant() != 0))
cast<MCSymbolMachO>(Symbol)->setAltEntry();
}
}
MCObjectStreamer::emitAssignment(Symbol, Value);
}
void MCMachOStreamer::emitDataRegion(DataRegionData::KindTy Kind) {
// Create a temporary label to mark the start of the data region.
MCSymbol *Start = getContext().createTempSymbol();
emitLabel(Start);
// Record the region for the object writer to use.
DataRegionData Data = { Kind, Start, nullptr };
std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
Regions.push_back(Data);
}
void MCMachOStreamer::emitDataRegionEnd() {
std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
assert(!Regions.empty() && "Mismatched .end_data_region!");
DataRegionData &Data = Regions.back();
assert(!Data.End && "Mismatched .end_data_region!");
// Create a temporary label to mark the end of the data region.
Data.End = getContext().createTempSymbol();
emitLabel(Data.End);
}
void MCMachOStreamer::emitAssemblerFlag(MCAssemblerFlag Flag) {
// Let the target do whatever target specific stuff it needs to do.
getAssembler().getBackend().handleAssemblerFlag(Flag);
// Do any generic stuff we need to do.
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;
}
}
void MCMachOStreamer::emitLinkerOptions(ArrayRef<std::string> Options) {
getAssembler().getLinkerOptions().push_back(Options);
}
void MCMachOStreamer::emitDataRegion(MCDataRegionType Kind) {
switch (Kind) {
case MCDR_DataRegion:
emitDataRegion(DataRegionData::Data);
return;
case MCDR_DataRegionJT8:
emitDataRegion(DataRegionData::JumpTable8);
return;
case MCDR_DataRegionJT16:
emitDataRegion(DataRegionData::JumpTable16);
return;
case MCDR_DataRegionJT32:
emitDataRegion(DataRegionData::JumpTable32);
return;
case MCDR_DataRegionEnd:
emitDataRegionEnd();
return;
}
}
void MCMachOStreamer::emitVersionMin(MCVersionMinType Kind, unsigned Major,
unsigned Minor, unsigned Update,
VersionTuple SDKVersion) {
getAssembler().setVersionMin(Kind, Major, Minor, Update, SDKVersion);
}
void MCMachOStreamer::emitBuildVersion(unsigned Platform, unsigned Major,
unsigned Minor, unsigned Update,
VersionTuple SDKVersion) {
getAssembler().setBuildVersion((MachO::PlatformType)Platform, Major, Minor,
Update, SDKVersion);
}
void MCMachOStreamer::emitDarwinTargetVariantBuildVersion(
unsigned Platform, unsigned Major, unsigned Minor, unsigned Update,
VersionTuple SDKVersion) {
getAssembler().setDarwinTargetVariantBuildVersion(
(MachO::PlatformType)Platform, Major, Minor, Update, SDKVersion);
}
void MCMachOStreamer::emitThumbFunc(MCSymbol *Symbol) {
// Remember that the function is a thumb function. Fixup and relocation
// values will need adjusted.
getAssembler().setIsThumbFunc(Symbol);
cast<MCSymbolMachO>(Symbol)->setThumbFunc();
}
bool MCMachOStreamer::emitSymbolAttribute(MCSymbol *Sym,
MCSymbolAttr Attribute) {
MCSymbolMachO *Symbol = cast<MCSymbolMachO>(Sym);
// 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.Section = getCurrentSectionOnly();
getAssembler().getIndirectSymbols().push_back(ISD);
return true;
}
// Adding a symbol attribute always introduces the symbol, note that an
// important side effect of calling registerSymbol here is to register
// the symbol with the assembler.
getAssembler().registerSymbol(*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_Invalid:
case MCSA_ELF_TypeFunction:
case MCSA_ELF_TypeIndFunction:
case MCSA_ELF_TypeObject:
case MCSA_ELF_TypeTLS:
case MCSA_ELF_TypeCommon:
case MCSA_ELF_TypeNoType:
case MCSA_ELF_TypeGnuUniqueObject:
case MCSA_Extern:
case MCSA_Hidden:
case MCSA_IndirectSymbol:
case MCSA_Internal:
case MCSA_Protected:
case MCSA_Weak:
case MCSA_Local:
case MCSA_LGlobal:
case MCSA_Exported:
case MCSA_Memtag:
case MCSA_WeakAntiDep:
return false;
case MCSA_Global:
Symbol->setExternal(true);
// This effectively clears the undefined lazy bit, in Darwin 'as', although
// it isn't very consistent because it implements this as part of symbol
// lookup.
//
// FIXME: Cleanup this code, these bits should be emitted based on semantic
// properties, not on the order of definition, etc.
Symbol->setReferenceTypeUndefinedLazy(false);
break;
case MCSA_LazyReference:
// FIXME: This requires -dynamic.
Symbol->setNoDeadStrip();
if (Symbol->isUndefined())
Symbol->setReferenceTypeUndefinedLazy(true);
break;
// Since .reference sets the no dead strip bit, it is equivalent to
// .no_dead_strip in practice.
case MCSA_Reference:
case MCSA_NoDeadStrip:
Symbol->setNoDeadStrip();
break;
case MCSA_SymbolResolver:
Symbol->setSymbolResolver();
break;
case MCSA_AltEntry:
Symbol->setAltEntry();
break;
case MCSA_PrivateExtern:
Symbol->setExternal(true);
Symbol->setPrivateExtern(true);
break;
case MCSA_WeakReference:
// FIXME: This requires -dynamic.
if (Symbol->isUndefined())
Symbol->setWeakReference();
break;
case MCSA_WeakDefinition:
// FIXME: 'as' enforces that this is defined and global. The manual claims
// it has to be in a coalesced section, but this isn't enforced.
Symbol->setWeakDefinition();
break;
case MCSA_WeakDefAutoPrivate:
Symbol->setWeakDefinition();
Symbol->setWeakReference();
break;
case MCSA_Cold:
Symbol->setCold();
break;
}
return true;
}
void MCMachOStreamer::emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
// Encode the 'desc' value into the lowest implementation defined bits.
getAssembler().registerSymbol(*Symbol);
cast<MCSymbolMachO>(Symbol)->setDesc(DescValue);
}
void MCMachOStreamer::emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
Align ByteAlignment) {
// FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
getAssembler().registerSymbol(*Symbol);
Symbol->setExternal(true);
Symbol->setCommon(Size, ByteAlignment);
}
void MCMachOStreamer::emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
Align ByteAlignment) {
// '.lcomm' is equivalent to '.zerofill'.
return emitZerofill(getContext().getObjectFileInfo()->getDataBSSSection(),
Symbol, Size, ByteAlignment);
}
void MCMachOStreamer::emitZerofill(MCSection *Section, MCSymbol *Symbol,
uint64_t Size, Align ByteAlignment,
SMLoc Loc) {
// On darwin all virtual sections have zerofill type. Disallow the usage of
// .zerofill in non-virtual functions. If something similar is needed, use
// .space or .zero.
if (!Section->isVirtualSection()) {
getContext().reportError(
Loc, "The usage of .zerofill is restricted to sections of "
"ZEROFILL type. Use .zero or .space instead.");
return; // Early returning here shouldn't harm. EmitZeros should work on any
// section.
}
pushSection();
switchSection(Section);
// The symbol may not be present, which only creates the section.
if (Symbol) {
emitValueToAlignment(ByteAlignment, 0, 1, 0);
emitLabel(Symbol);
emitZeros(Size);
}
popSection();
}
// This should always be called with the thread local bss section. Like the
// .zerofill directive this doesn't actually switch sections on us.
void MCMachOStreamer::emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
uint64_t Size, Align ByteAlignment) {
emitZerofill(Section, Symbol, Size, ByteAlignment);
}
void MCMachOStreamer::emitInstToData(const MCInst &Inst,
const MCSubtargetInfo &STI) {
MCDataFragment *DF = getOrCreateDataFragment();
SmallVector<MCFixup, 4> Fixups;
SmallString<256> Code;
getAssembler().getEmitter().encodeInstruction(Inst, Code, Fixups, STI);
// Add the fixups and data.
for (MCFixup &Fixup : Fixups) {
Fixup.setOffset(Fixup.getOffset() + DF->getContents().size());
DF->getFixups().push_back(Fixup);
}
DF->setHasInstructions(STI);
DF->getContents().append(Code.begin(), Code.end());
}
void MCMachOStreamer::finishImpl() {
emitFrames(&getAssembler().getBackend());
// We have to set the fragment atom associations so we can relax properly for
// Mach-O.
// First, scan the symbol table to build a lookup table from fragments to
// defining symbols.
DenseMap<const MCFragment *, const MCSymbol *> DefiningSymbolMap;
for (const MCSymbol &Symbol : getAssembler().symbols()) {
if (getAssembler().isSymbolLinkerVisible(Symbol) && Symbol.isInSection() &&
!Symbol.isVariable()) {
// An atom defining symbol should never be internal to a fragment.
assert(Symbol.getOffset() == 0 &&
"Invalid offset in atom defining symbol!");
DefiningSymbolMap[Symbol.getFragment()] = &Symbol;
}
}
// Set the fragment atom associations by tracking the last seen atom defining
// symbol.
for (MCSection &Sec : getAssembler()) {
const MCSymbol *CurrentAtom = nullptr;
for (MCFragment &Frag : Sec) {
if (const MCSymbol *Symbol = DefiningSymbolMap.lookup(&Frag))
CurrentAtom = Symbol;
Frag.setAtom(CurrentAtom);
}
}
finalizeCGProfile();
createAddrSigSection();
this->MCObjectStreamer::finishImpl();
}
void MCMachOStreamer::finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE) {
const MCSymbol *S = &SRE->getSymbol();
if (getAssembler().registerSymbol(*S))
S->setExternal(true);
}
void MCMachOStreamer::finalizeCGProfile() {
MCAssembler &Asm = getAssembler();
if (Asm.CGProfile.empty())
return;
for (MCAssembler::CGProfileEntry &E : Asm.CGProfile) {
finalizeCGProfileEntry(E.From);
finalizeCGProfileEntry(E.To);
}
// We can't write the section out until symbol indices are finalized which
// doesn't happen until after section layout. We need to create the section
// and set its size now so that it's accounted for in layout.
MCSection *CGProfileSection = Asm.getContext().getMachOSection(
"__LLVM", "__cg_profile", 0, SectionKind::getMetadata());
Asm.registerSection(*CGProfileSection);
auto *Frag = new MCDataFragment(CGProfileSection);
// For each entry, reserve space for 2 32-bit indices and a 64-bit count.
size_t SectionBytes =
Asm.CGProfile.size() * (2 * sizeof(uint32_t) + sizeof(uint64_t));
Frag->getContents().resize(SectionBytes);
}
MCStreamer *llvm::createMachOStreamer(MCContext &Context,
std::unique_ptr<MCAsmBackend> &&MAB,
std::unique_ptr<MCObjectWriter> &&OW,
std::unique_ptr<MCCodeEmitter> &&CE,
bool RelaxAll, bool DWARFMustBeAtTheEnd,
bool LabelSections) {
MCMachOStreamer *S =
new MCMachOStreamer(Context, std::move(MAB), std::move(OW), std::move(CE),
DWARFMustBeAtTheEnd, LabelSections);
const Triple &Target = Context.getTargetTriple();
S->emitVersionForTarget(
Target, Context.getObjectFileInfo()->getSDKVersion(),
Context.getObjectFileInfo()->getDarwinTargetVariantTriple(),
Context.getObjectFileInfo()->getDarwinTargetVariantSDKVersion());
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
return S;
}
// The AddrSig section uses a series of relocations to refer to the symbols that
// should be considered address-significant. The only interesting content of
// these relocations is their symbol; the type, length etc will be ignored by
// the linker. The reason we are not referring to the symbol indices directly is
// that those indices will be invalidated by tools that update the symbol table.
// Symbol relocations OTOH will have their indices updated by e.g. llvm-strip.
void MCMachOStreamer::createAddrSigSection() {
MCAssembler &Asm = getAssembler();
MCObjectWriter &writer = Asm.getWriter();
if (!writer.getEmitAddrsigSection())
return;
// Create the AddrSig section and first data fragment here as its layout needs
// to be computed immediately after in order for it to be exported correctly.
MCSection *AddrSigSection =
Asm.getContext().getObjectFileInfo()->getAddrSigSection();
Asm.registerSection(*AddrSigSection);
auto *Frag = new MCDataFragment(AddrSigSection);
// We will generate a series of pointer-sized symbol relocations at offset
// 0x0. Set the section size to be large enough to contain a single pointer
// (instead of emitting a zero-sized section) so these relocations are
// technically valid, even though we don't expect these relocations to
// actually be applied by the linker.
Frag->getContents().resize(8);
}