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//===-------- PPCELFStreamer.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 is a custom MCELFStreamer for PowerPC.
//
// The purpose of the custom ELF streamer is to allow us to intercept
// instructions as they are being emitted and align all 8 byte instructions
// to a 64 byte boundary if required (by adding a 4 byte nop). This is important
// because 8 byte instructions are not allowed to cross 64 byte boundaries
// and by aliging anything that is within 4 bytes of the boundary we can
// guarantee that the 8 byte instructions do not cross that boundary.
//
//===----------------------------------------------------------------------===//
#include "PPCELFStreamer.h"
#include "PPCInstrInfo.h"
#include "PPCMCCodeEmitter.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/SourceMgr.h"
using namespace llvm;
PPCELFStreamer::PPCELFStreamer(MCContext &Context,
std::unique_ptr<MCAsmBackend> MAB,
std::unique_ptr<MCObjectWriter> OW,
std::unique_ptr<MCCodeEmitter> Emitter)
: MCELFStreamer(Context, std::move(MAB), std::move(OW),
std::move(Emitter)), LastLabel(NULL) {
}
void PPCELFStreamer::emitPrefixedInstruction(const MCInst &Inst,
const MCSubtargetInfo &STI) {
// Prefixed instructions must not cross a 64-byte boundary (i.e. prefix is
// before the boundary and the remaining 4-bytes are after the boundary). In
// order to achieve this, a nop is added prior to any such boundary-crossing
// prefixed instruction. Align to 64 bytes if possible but add a maximum of 4
// bytes when trying to do that. If alignment requires adding more than 4
// bytes then the instruction won't be aligned. When emitting a code alignment
// a new fragment is created for this alignment. This fragment will contain
// all of the nops required as part of the alignment operation. In the cases
// when no nops are added then The fragment is still created but it remains
// empty.
emitCodeAlignment(64, 4);
// Emit the instruction.
// Since the previous emit created a new fragment then adding this instruction
// also forces the addition of a new fragment. Inst is now the first
// instruction in that new fragment.
MCELFStreamer::emitInstruction(Inst, STI);
// The above instruction is forced to start a new fragment because it
// comes after a code alignment fragment. Get that new fragment.
MCFragment *InstructionFragment = getCurrentFragment();
SMLoc InstLoc = Inst.getLoc();
// Check if there was a last label emitted.
if (LastLabel && !LastLabel->isUnset() && LastLabelLoc.isValid() &&
InstLoc.isValid()) {
const SourceMgr *SourceManager = getContext().getSourceManager();
unsigned InstLine = SourceManager->FindLineNumber(InstLoc);
unsigned LabelLine = SourceManager->FindLineNumber(LastLabelLoc);
// If the Label and the Instruction are on the same line then move the
// label to the top of the fragment containing the aligned instruction that
// was just added.
if (InstLine == LabelLine) {
AssignFragment(LastLabel, InstructionFragment);
LastLabel->setOffset(0);
}
}
}
void PPCELFStreamer::emitInstruction(const MCInst &Inst,
const MCSubtargetInfo &STI) {
PPCMCCodeEmitter *Emitter =
static_cast<PPCMCCodeEmitter*>(getAssembler().getEmitterPtr());
// Special handling is only for prefixed instructions.
if (!Emitter->isPrefixedInstruction(Inst)) {
MCELFStreamer::emitInstruction(Inst, STI);
return;
}
emitPrefixedInstruction(Inst, STI);
}
void PPCELFStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
LastLabel = Symbol;
LastLabelLoc = Loc;
MCELFStreamer::emitLabel(Symbol);
}
MCELFStreamer *llvm::createPPCELFStreamer(
MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
std::unique_ptr<MCObjectWriter> OW,
std::unique_ptr<MCCodeEmitter> Emitter) {
return new PPCELFStreamer(Context, std::move(MAB), std::move(OW),
std::move(Emitter));
}
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