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//===- lib/MC/AArch64ELFStreamer.cpp - ELF Object Output for AArch64 ------===//
//
// 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 AArch64 ELF .o object files. Different
// from generic ELF streamer in emitting mapping symbols ($x and $d) to delimit
// regions of data and code.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCELFStreamer.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCELF.h"
#include "llvm/MC/MCELFStreamer.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/MCStreamer.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;
namespace {
/// Extend the generic ELFStreamer class so that it can emit mapping symbols at
/// the appropriate points in the object files. These symbols are defined in the
/// AArch64 ELF ABI:
/// infocenter.arm.com/help/topic/com.arm.doc.ihi0056a/IHI0056A_aaelf64.pdf
///
/// In brief: $x or $d should be emitted at the start of each contiguous region
/// of A64 code or data in a section. In practice, this emission does not rely
/// on explicit assembler directives but on inherent properties of the
/// directives doing the emission (e.g. ".byte" is data, "add x0, x0, x0" an
/// instruction).
///
/// As a result this system is orthogonal to the DataRegion infrastructure used
/// by MachO. Beware!
class AArch64ELFStreamer : public MCELFStreamer {
public:
AArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *Emitter)
: MCELFStreamer(Context, TAB, OS, Emitter),
MappingSymbolCounter(0), LastEMS(EMS_None) {
}
~AArch64ELFStreamer() {}
virtual void ChangeSection(const MCSection *Section,
const MCExpr *Subsection) {
// We have to keep track of the mapping symbol state of any sections we
// use. Each one should start off as EMS_None, which is provided as the
// default constructor by DenseMap::lookup.
LastMappingSymbols[getPreviousSection().first] = LastEMS;
LastEMS = LastMappingSymbols.lookup(Section);
MCELFStreamer::ChangeSection(Section, Subsection);
}
/// This function is the one used to emit instruction data into the ELF
/// streamer. We override it to add the appropriate mapping symbol if
/// necessary.
virtual void EmitInstruction(const MCInst& Inst) {
EmitA64MappingSymbol();
MCELFStreamer::EmitInstruction(Inst);
}
/// This is one of the functions used to emit data into an ELF section, so the
/// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
/// if necessary.
virtual void EmitBytes(StringRef Data) {
EmitDataMappingSymbol();
MCELFStreamer::EmitBytes(Data);
}
/// This is one of the functions used to emit data into an ELF section, so the
/// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
/// if necessary.
virtual void EmitValueImpl(const MCExpr *Value, unsigned Size) {
EmitDataMappingSymbol();
MCELFStreamer::EmitValueImpl(Value, Size);
}
private:
enum ElfMappingSymbol {
EMS_None,
EMS_A64,
EMS_Data
};
void EmitDataMappingSymbol() {
if (LastEMS == EMS_Data) return;
EmitMappingSymbol("$d");
LastEMS = EMS_Data;
}
void EmitA64MappingSymbol() {
if (LastEMS == EMS_A64) return;
EmitMappingSymbol("$x");
LastEMS = EMS_A64;
}
void EmitMappingSymbol(StringRef Name) {
MCSymbol *Start = getContext().CreateTempSymbol();
EmitLabel(Start);
MCSymbol *Symbol =
getContext().GetOrCreateSymbol(Name + "." +
Twine(MappingSymbolCounter++));
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
MCELF::SetType(SD, ELF::STT_NOTYPE);
MCELF::SetBinding(SD, ELF::STB_LOCAL);
SD.setExternal(false);
Symbol->setSection(*getCurrentSection().first);
const MCExpr *Value = MCSymbolRefExpr::Create(Start, getContext());
Symbol->setVariableValue(Value);
}
int64_t MappingSymbolCounter;
DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
ElfMappingSymbol LastEMS;
/// @}
};
}
namespace llvm {
MCELFStreamer* createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *Emitter,
bool RelaxAll, bool NoExecStack) {
AArch64ELFStreamer *S = new AArch64ELFStreamer(Context, TAB, OS, Emitter);
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
if (NoExecStack)
S->getAssembler().setNoExecStack(true);
return S;
}
}
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