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

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//===- lib/MC/MCMachOStreamer.cpp - Mach-O Object Output ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetAsmBackend.h"
using namespace llvm;
namespace {
class MCMachOStreamer : public MCStreamer {
/// SymbolFlags - We store the value for the 'desc' symbol field in the lowest
/// 16 bits of the implementation defined flags.
enum SymbolFlags { // See <mach-o/nlist.h>.
SF_DescFlagsMask = 0xFFFF,
// Reference type flags.
SF_ReferenceTypeMask = 0x0007,
SF_ReferenceTypeUndefinedNonLazy = 0x0000,
SF_ReferenceTypeUndefinedLazy = 0x0001,
SF_ReferenceTypeDefined = 0x0002,
SF_ReferenceTypePrivateDefined = 0x0003,
SF_ReferenceTypePrivateUndefinedNonLazy = 0x0004,
SF_ReferenceTypePrivateUndefinedLazy = 0x0005,
// Other 'desc' flags.
SF_NoDeadStrip = 0x0020,
SF_WeakReference = 0x0040,
SF_WeakDefinition = 0x0080
};
private:
MCAssembler Assembler;
MCSectionData *CurSectionData;
private:
MCFragment *getCurrentFragment() const {
assert(CurSectionData && "No current section!");
if (!CurSectionData->empty())
return &CurSectionData->getFragmentList().back();
return 0;
}
/// Get a data fragment to write into, creating a new one if the current
/// fragment is not a data fragment.
MCDataFragment *getOrCreateDataFragment() const {
MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
if (!F)
F = new MCDataFragment(CurSectionData);
return F;
}
public:
MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
raw_ostream &_OS, MCCodeEmitter *_Emitter)
: MCStreamer(Context), Assembler(Context, TAB, *_Emitter, _OS),
CurSectionData(0) {}
~MCMachOStreamer() {}
MCAssembler &getAssembler() { return Assembler; }
const MCExpr *AddValueSymbols(const MCExpr *Value) {
switch (Value->getKind()) {
case MCExpr::Target: assert(0 && "Can't handle target exprs yet!");
case MCExpr::Constant:
break;
case MCExpr::Binary: {
const MCBinaryExpr *BE = cast<MCBinaryExpr>(Value);
AddValueSymbols(BE->getLHS());
AddValueSymbols(BE->getRHS());
break;
}
case MCExpr::SymbolRef:
Assembler.getOrCreateSymbolData(
cast<MCSymbolRefExpr>(Value)->getSymbol());
break;
case MCExpr::Unary:
AddValueSymbols(cast<MCUnaryExpr>(Value)->getSubExpr());
break;
}
return Value;
}
/// @name MCStreamer Interface
/// @{
virtual void SwitchSection(const MCSection *Section);
virtual void EmitLabel(MCSymbol *Symbol);
virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment);
virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
assert(0 && "macho doesn't support this directive");
}
virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
assert(0 && "macho doesn't support this directive");
}
virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
unsigned Size = 0, unsigned ByteAlignment = 0);
virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
virtual void EmitGPRel32Value(const MCExpr *Value) {
assert(0 && "macho doesn't support this directive");
}
virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
unsigned ValueSize = 1,
unsigned MaxBytesToEmit = 0);
virtual void EmitCodeAlignment(unsigned ByteAlignment,
unsigned MaxBytesToEmit = 0);
virtual void EmitValueToOffset(const MCExpr *Offset,
unsigned char Value = 0);
virtual void EmitFileDirective(StringRef Filename) {
errs() << "FIXME: MCMachoStreamer:EmitFileDirective not implemented\n";
}
virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
errs() << "FIXME: MCMachoStreamer:EmitDwarfFileDirective not implemented\n";
}
virtual void EmitInstruction(const MCInst &Inst);
virtual void Finish();
/// @}
};
} // end anonymous namespace.
void MCMachOStreamer::SwitchSection(const MCSection *Section) {
assert(Section && "Cannot switch to a null section!");
// If already in this section, then this is a noop.
if (Section == CurSection) return;
CurSection = Section;
CurSectionData = &Assembler.getOrCreateSectionData(*Section);
}
void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
// FIXME: This is wasteful, we don't necessarily need to create a data
// fragment. Instead, we should mark the symbol as pointing into the data
// fragment if it exists, otherwise we should just queue the label and set its
// fragment pointer when we emit the next fragment.
MCDataFragment *F = getOrCreateDataFragment();
MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
SD.setFragment(F);
SD.setOffset(F->getContents().size());
// This causes the reference type and weak reference flags to be cleared.
SD.setFlags(SD.getFlags() & ~(SF_WeakReference | SF_ReferenceTypeMask));
Symbol->setSection(*CurSection);
}
void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
switch (Flag) {
case MCAF_SubsectionsViaSymbols:
Assembler.setSubsectionsViaSymbols(true);
return;
}
assert(0 && "invalid assembler flag!");
}
void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
// Only absolute symbols can be redefined.
assert((Symbol->isUndefined() || Symbol->isAbsolute()) &&
"Cannot define a symbol twice!");
// FIXME: Lift context changes into super class.
// FIXME: Set associated section.
Symbol->setValue(AddValueSymbols(Value));
}
void MCMachOStreamer::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 = CurSectionData;
Assembler.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 = Assembler.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_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_IndirectSymbol:
case MCSA_Hidden:
case MCSA_Internal:
case MCSA_Protected:
case MCSA_Weak:
case MCSA_Local:
assert(0 && "Invalid symbol attribute for Mach-O!");
break;
case MCSA_Global:
SD.setExternal(true);
break;
case MCSA_LazyReference:
// FIXME: This requires -dynamic.
SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
if (Symbol->isUndefined())
SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
break;
// Since .reference sets the no dead strip bit, it is equivalent to
// .no_dead_strip in practice.
case MCSA_Reference:
case MCSA_NoDeadStrip:
SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
break;
case MCSA_PrivateExtern:
SD.setExternal(true);
SD.setPrivateExtern(true);
break;
case MCSA_WeakReference:
// FIXME: This requires -dynamic.
if (Symbol->isUndefined())
SD.setFlags(SD.getFlags() | SF_WeakReference);
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.
SD.setFlags(SD.getFlags() | SF_WeakDefinition);
break;
}
}
void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
// Encode the 'desc' value into the lowest implementation defined bits.
assert(DescValue == (DescValue & SF_DescFlagsMask) &&
"Invalid .desc value!");
Assembler.getOrCreateSymbolData(*Symbol).setFlags(DescValue&SF_DescFlagsMask);
}
void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
// FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
SD.setExternal(true);
SD.setCommon(Size, ByteAlignment);
}
void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
unsigned Size, unsigned ByteAlignment) {
MCSectionData &SectData = Assembler.getOrCreateSectionData(*Section);
// The symbol may not be present, which only creates the section.
if (!Symbol)
return;
// FIXME: Assert that this section has the zerofill type.
assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
MCSymbolData &SD = Assembler.getOrCreateSymbolData(*Symbol);
MCFragment *F = new MCZeroFillFragment(Size, ByteAlignment, &SectData);
SD.setFragment(F);
Symbol->setSection(*Section);
// Update the maximum alignment on the zero fill section if necessary.
if (ByteAlignment > SectData.getAlignment())
SectData.setAlignment(ByteAlignment);
}
void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
}
void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size,
unsigned AddrSpace) {
MCDataFragment *DF = getOrCreateDataFragment();
// Avoid fixups when possible.
int64_t AbsValue;
if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
// FIXME: Endianness assumption.
for (unsigned i = 0; i != Size; ++i)
DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
} else {
DF->addFixup(MCAsmFixup(DF->getContents().size(), *AddValueSymbols(Value),
MCFixup::getKindForSize(Size)));
DF->getContents().resize(DF->getContents().size() + Size, 0);
}
}
void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
int64_t Value, unsigned ValueSize,
unsigned MaxBytesToEmit) {
if (MaxBytesToEmit == 0)
MaxBytesToEmit = ByteAlignment;
new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
false /* EmitNops */, CurSectionData);
// Update the maximum alignment on the current section if necessary.
if (ByteAlignment > CurSectionData->getAlignment())
CurSectionData->setAlignment(ByteAlignment);
}
void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
unsigned MaxBytesToEmit) {
if (MaxBytesToEmit == 0)
MaxBytesToEmit = ByteAlignment;
new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
true /* EmitNops */, CurSectionData);
// Update the maximum alignment on the current section if necessary.
if (ByteAlignment > CurSectionData->getAlignment())
CurSectionData->setAlignment(ByteAlignment);
}
void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
unsigned char Value) {
new MCOrgFragment(*Offset, Value, CurSectionData);
}
void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
// Scan for values.
for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
if (Inst.getOperand(i).isExpr())
AddValueSymbols(Inst.getOperand(i).getExpr());
CurSectionData->setHasInstructions(true);
// FIXME-PERF: Common case is that we don't need to relax, encode directly
// onto the data fragments buffers.
SmallVector<MCFixup, 4> Fixups;
SmallString<256> Code;
raw_svector_ostream VecOS(Code);
Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
VecOS.flush();
// FIXME: Eliminate this copy.
SmallVector<MCAsmFixup, 4> AsmFixups;
for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
MCFixup &F = Fixups[i];
AsmFixups.push_back(MCAsmFixup(F.getOffset(), *F.getValue(),
F.getKind()));
}
// See if we might need to relax this instruction, if so it needs its own
// fragment.
//
// FIXME-PERF: Support target hook to do a fast path that avoids the encoder,
// when we can immediately tell that we will get something which might need
// relaxation (and compute its size).
//
// FIXME-PERF: We should also be smart about immediately relaxing instructions
// which we can already show will never possibly fit (we can also do a very
// good job of this before we do the first relaxation pass, because we have
// total knowledge about undefined symbols at that point). Even now, though,
// we can do a decent job, especially on Darwin where scattering means that we
// are going to often know that we can never fully resolve a fixup.
if (Assembler.getBackend().MayNeedRelaxation(Inst, AsmFixups)) {
MCInstFragment *IF = new MCInstFragment(Inst, CurSectionData);
// Add the fixups and data.
//
// FIXME: Revisit this design decision when relaxation is done, we may be
// able to get away with not storing any extra data in the MCInst.
IF->getCode() = Code;
IF->getFixups() = AsmFixups;
return;
}
// Add the fixups and data.
MCDataFragment *DF = getOrCreateDataFragment();
for (unsigned i = 0, e = AsmFixups.size(); i != e; ++i) {
AsmFixups[i].Offset += DF->getContents().size();
DF->addFixup(AsmFixups[i]);
}
DF->getContents().append(Code.begin(), Code.end());
}
void MCMachOStreamer::Finish() {
Assembler.Finish();
}
MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *CE,
bool RelaxAll) {
MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
return S;
}
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