llvm-project/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp

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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 "AArch64TargetStreamer.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Triple.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/MCELFStreamer.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
namespace {
class AArch64ELFStreamer;
class AArch64TargetAsmStreamer : public AArch64TargetStreamer {
formatted_raw_ostream &OS;
void emitInst(uint32_t Inst) override;
public:
AArch64TargetAsmStreamer(MCStreamer &S, formatted_raw_ostream &OS);
};
AArch64TargetAsmStreamer::AArch64TargetAsmStreamer(MCStreamer &S,
formatted_raw_ostream &OS)
: AArch64TargetStreamer(S), OS(OS) {}
void AArch64TargetAsmStreamer::emitInst(uint32_t Inst) {
OS << "\t.inst\t0x" << Twine::utohexstr(Inst) << "\n";
}
class AArch64TargetELFStreamer : public AArch64TargetStreamer {
private:
AArch64ELFStreamer &getStreamer();
void emitInst(uint32_t Inst) override;
public:
AArch64TargetELFStreamer(MCStreamer &S) : AArch64TargetStreamer(S) {}
};
/// 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:
friend class AArch64TargetELFStreamer;
AArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
raw_pwrite_stream &OS, MCCodeEmitter *Emitter)
: MCELFStreamer(Context, TAB, OS, Emitter), MappingSymbolCounter(0),
LastEMS(EMS_None) {}
void ChangeSection(MCSection *Section, const MCExpr *Subsection) override {
// 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.
void EmitInstruction(const MCInst &Inst,
const MCSubtargetInfo &STI) override {
EmitA64MappingSymbol();
MCELFStreamer::EmitInstruction(Inst, STI);
}
/// Emit a 32-bit value as an instruction. This is only used for the .inst
/// directive, EmitInstruction should be used in other cases.
void emitInst(uint32_t Inst) {
char Buffer[4];
// We can't just use EmitIntValue here, as that will emit a data mapping
// symbol, and swap the endianness on big-endian systems (instructions are
// always little-endian).
for (unsigned I = 0; I < 4; ++I) {
Buffer[I] = uint8_t(Inst);
Inst >>= 8;
}
EmitA64MappingSymbol();
MCELFStreamer::EmitBytes(StringRef(Buffer, 4));
}
/// 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.
void EmitBytes(StringRef Data) override {
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 ($d)
/// if necessary.
void EmitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
EmitDataMappingSymbol();
MCELFStreamer::EmitValueImpl(Value, Size, Loc);
}
private:
enum ElfMappingSymbol {
EMS_None,
EMS_A64,
EMS_Data
};
void EmitDataMappingSymbol() {
if (LastEMS == EMS_Data)
return;
EmitMappingSymbol("$d");
LastEMS = EMS_Data;
}
void EmitA64MappingSymbol() {
if (LastEMS == EMS_A64)
return;
EmitMappingSymbol("$x");
LastEMS = EMS_A64;
}
void EmitMappingSymbol(StringRef Name) {
auto *Symbol = cast<MCSymbolELF>(getContext().getOrCreateSymbol(
Name + "." + Twine(MappingSymbolCounter++)));
EmitLabel(Symbol);
Symbol->setType(ELF::STT_NOTYPE);
Symbol->setBinding(ELF::STB_LOCAL);
Symbol->setExternal(false);
}
int64_t MappingSymbolCounter;
DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
ElfMappingSymbol LastEMS;
};
} // end anonymous namespace
AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
return static_cast<AArch64ELFStreamer &>(Streamer);
}
void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
getStreamer().emitInst(Inst);
}
namespace llvm {
MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
formatted_raw_ostream &OS,
MCInstPrinter *InstPrint,
bool isVerboseAsm) {
return new AArch64TargetAsmStreamer(S, OS);
}
MCELFStreamer *createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
raw_pwrite_stream &OS,
MCCodeEmitter *Emitter, bool RelaxAll) {
AArch64ELFStreamer *S = new AArch64ELFStreamer(Context, TAB, OS, Emitter);
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
return S;
}
MCTargetStreamer *
createAArch64ObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
const Triple &TT = STI.getTargetTriple();
if (TT.isOSBinFormatELF())
return new AArch64TargetELFStreamer(S);
return nullptr;
}
} // end namespace llvm