wangtao
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
llvm-project/llvm/lib/MC/MCELFStreamer.cpp

403 lines
14 KiB
C++
Raw Blame History

//===- 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/MCStreamer.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCCodeEmitter.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/Support/Debug.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetAsmBackend.h"
using namespace llvm;
namespace {
class MCELFStreamer : public MCObjectStreamer {
public:
MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *Emitter)
: MCObjectStreamer(Context, TAB, OS, Emitter) {}
~MCELFStreamer() {}
/// @name MCStreamer Interface
/// @{
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) {
assert(0 && "ELF doesn't support this directive");
}
virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment);
virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
assert(0 && "ELF doesn't support this directive");
}
virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
assert(0 && "ELF doesn't support this directive");
}
virtual void EmitCOFFSymbolType(int Type) {
assert(0 && "ELF doesn't support this directive");
}
virtual void EndCOFFSymbolDef() {
assert(0 && "ELF doesn't support this directive");
}
virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
SD.setSize(Value);
}
virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
assert(0 && "ELF doesn't support this directive");
}
virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
unsigned Size = 0, unsigned ByteAlignment = 0) {
assert(0 && "ELF doesn't support this directive");
}
virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
uint64_t Size, unsigned ByteAlignment = 0) {
assert(0 && "ELF doesn't support this directive");
}
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 && "ELF 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);
virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
DEBUG(dbgs() << "FIXME: MCELFStreamer:EmitDwarfFileDirective not implemented\n");
}
virtual void EmitInstruction(const MCInst &Inst);
virtual void Finish();
/// @}
};
} // end anonymous namespace.
void MCELFStreamer::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 = getAssembler().getOrCreateSymbolData(*Symbol);
assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
SD.setFragment(F);
SD.setOffset(F->getContents().size());
Symbol->setSection(*CurSection);
}
void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
switch (Flag) {
case MCAF_SubsectionsViaSymbols:
getAssembler().setSubsectionsViaSymbols(true);
return;
}
assert(0 && "invalid assembler flag!");
}
void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
// MCObjectStreamer.
// FIXME: Lift context changes into super class.
getAssembler().getOrCreateSymbolData(*Symbol);
Symbol->setVariableValue(AddValueSymbols(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_NoDeadStrip:
case MCSA_PrivateExtern:
case MCSA_WeakReference:
case MCSA_WeakDefinition:
case MCSA_WeakDefAutoPrivate:
case MCSA_Invalid:
case MCSA_ELF_TypeIndFunction:
case MCSA_IndirectSymbol:
assert(0 && "Invalid symbol attribute for ELF!");
break;
case MCSA_Global:
SD.setFlags(SD.getFlags() | ELF_STB_Global);
SD.setExternal(true);
break;
case MCSA_Weak:
SD.setFlags(SD.getFlags() | ELF_STB_Weak);
break;
case MCSA_Local:
SD.setFlags(SD.getFlags() | ELF_STB_Local);
break;
case MCSA_ELF_TypeFunction:
SD.setFlags(SD.getFlags() | ELF_STT_Func);
break;
case MCSA_ELF_TypeObject:
SD.setFlags(SD.getFlags() | ELF_STT_Object);
break;
case MCSA_ELF_TypeTLS:
SD.setFlags(SD.getFlags() | ELF_STT_Tls);
break;
case MCSA_ELF_TypeCommon:
SD.setFlags(SD.getFlags() | ELF_STT_Common);
break;
case MCSA_ELF_TypeNoType:
SD.setFlags(SD.getFlags() | ELF_STT_Notype);
break;
case MCSA_Protected:
SD.setFlags(SD.getFlags() | ELF_STV_Protected);
break;
case MCSA_Hidden:
SD.setFlags(SD.getFlags() | ELF_STV_Hidden);
break;
case MCSA_Internal:
SD.setFlags(SD.getFlags() | ELF_STV_Internal);
break;
}
}
void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
unsigned ByteAlignment) {
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
if ((SD.getFlags() & (0xf << ELF_STB_Shift)) == ELF_STB_Local) {
const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
MCSectionELF::SHT_NOBITS,
MCSectionELF::SHF_WRITE |
MCSectionELF::SHF_ALLOC,
SectionKind::getBSS());
MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
SD.setFragment(F);
Symbol->setSection(*Section);
SD.setSize(MCConstantExpr::Create(Size, getContext()));
} else {
SD.setExternal(true);
}
SD.setCommon(Size, ByteAlignment);
}
void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
// MCObjectStreamer.
getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
}
void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
unsigned AddrSpace) {
// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
// MCObjectStreamer.
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(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
MCFixup::getKindForSize(Size)));
DF->getContents().resize(DF->getContents().size() + Size, 0);
}
}
void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
int64_t Value, unsigned ValueSize,
unsigned MaxBytesToEmit) {
// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
// MCObjectStreamer.
if (MaxBytesToEmit == 0)
MaxBytesToEmit = ByteAlignment;
new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
getCurrentSectionData());
// Update the maximum alignment on the current section if necessary.
if (ByteAlignment > getCurrentSectionData()->getAlignment())
getCurrentSectionData()->setAlignment(ByteAlignment);
}
void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
unsigned MaxBytesToEmit) {
// TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
// MCObjectStreamer.
if (MaxBytesToEmit == 0)
MaxBytesToEmit = ByteAlignment;
MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
getCurrentSectionData());
F->setEmitNops(true);
// Update the maximum alignment on the current section if necessary.
if (ByteAlignment > getCurrentSectionData()->getAlignment())
getCurrentSectionData()->setAlignment(ByteAlignment);
}
void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
unsigned char Value) {
// TODO: This is exactly the same as MCMachOStreamer. Consider merging into
// MCObjectStreamer.
new MCOrgFragment(*Offset, Value, getCurrentSectionData());
}
// 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(*CurSection);
Symbol->setAbsolute();
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
}
void MCELFStreamer::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());
getCurrentSectionData()->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);
getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
VecOS.flush();
// FIXME: Eliminate this copy.
SmallVector<MCFixup, 4> AsmFixups;
for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
MCFixup &F = Fixups[i];
AsmFixups.push_back(MCFixup::Create(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 (getAssembler().getBackend().MayNeedRelaxation(Inst)) {
MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
// 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].setOffset(AsmFixups[i].getOffset() + DF->getContents().size());
DF->addFixup(AsmFixups[i]);
}
DF->getContents().append(Code.begin(), Code.end());
}
void MCELFStreamer::Finish() {
getAssembler().Finish();
}
MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *CE,
bool RelaxAll) {
MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
return S;
}
Reference in New Issue View Git Blame Copy Permalink