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//===- lib/MC/ARMELFStreamer.cpp - ELF Object Output for ARM --------------===//
//
// 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 ARM ELF .o object files. Different
// from generic ELF streamer in emitting mapping symbols ($a, $t and $d) to
// delimit regions of data and code.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCELFStreamer.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCStreamer.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/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/MCAsmBackend.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
/// ARM ELF ABI: infocenter.arm.com/help/topic/com.arm.../IHI0044D_aaelf.pdf.
///
/// In brief: $a, $t or $d should be emitted at the start of each contiguous
/// region of ARM code, Thumb code or data in a section. In practice, this
/// emission does not rely on explicit assembler directives but on inherent
/// properties of the directives doing the emission (e.g. ".byte" is data, "add
/// r0, r0, r0" an instruction).
///
/// As a result this system is orthogonal to the DataRegion infrastructure used
/// by MachO. Beware!
class ARMELFStreamer : public MCELFStreamer {
public:
ARMELFStreamer(MCContext &Context, MCAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *Emitter, bool IsThumb)
: MCELFStreamer(Context, TAB, OS, Emitter),
IsThumb(IsThumb), MappingSymbolCounter(0), LastEMS(EMS_None) {
}
~ARMELFStreamer() {}
virtual void ChangeSection(const MCSection *Section) {
// We have to keep track of the mapping symbol state of any sections we
// use. Each one should start off as EMS_None, which is provided as the
// default constructor by DenseMap::lookup.
LastMappingSymbols[getPreviousSection()] = LastEMS;
LastEMS = LastMappingSymbols.lookup(Section);
MCELFStreamer::ChangeSection(Section);
}
/// This function is the one used to emit instruction data into the ELF
/// streamer. We override it to add the appropriate mapping symbol if
/// necessary.
virtual void EmitInstruction(const MCInst& Inst) {
if (IsThumb)
EmitThumbMappingSymbol();
else
EmitARMMappingSymbol();
MCELFStreamer::EmitInstruction(Inst);
}
/// This is one of the functions used to emit data into an ELF section, so the
/// ARM streamer overrides it to add the appropriate mapping symbol ($d) if
/// necessary.
virtual void EmitBytes(StringRef Data, unsigned AddrSpace) {
EmitDataMappingSymbol();
MCELFStreamer::EmitBytes(Data, AddrSpace);
}
/// This is one of the functions used to emit data into an ELF section, so the
/// ARM streamer overrides it to add the appropriate mapping symbol ($d) if
/// necessary.
virtual void EmitValueImpl(const MCExpr *Value, unsigned Size,
unsigned AddrSpace) {
EmitDataMappingSymbol();
MCELFStreamer::EmitValueImpl(Value, Size, AddrSpace);
}
virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {
MCELFStreamer::EmitAssemblerFlag(Flag);
switch (Flag) {
case MCAF_SyntaxUnified:
return; // no-op here.
case MCAF_Code16:
IsThumb = true;
return; // Change to Thumb mode
case MCAF_Code32:
IsThumb = false;
return; // Change to ARM mode
case MCAF_Code64:
return;
case MCAF_SubsectionsViaSymbols:
return;
}
}
private:
enum ElfMappingSymbol {
EMS_None,
EMS_ARM,
EMS_Thumb,
EMS_Data
};
void EmitDataMappingSymbol() {
if (LastEMS == EMS_Data) return;
EmitMappingSymbol("$d");
LastEMS = EMS_Data;
}
void EmitThumbMappingSymbol() {
if (LastEMS == EMS_Thumb) return;
EmitMappingSymbol("$t");
LastEMS = EMS_Thumb;
}
void EmitARMMappingSymbol() {
if (LastEMS == EMS_ARM) return;
EmitMappingSymbol("$a");
LastEMS = EMS_ARM;
}
void EmitMappingSymbol(StringRef Name) {
MCSymbol *Start = getContext().CreateTempSymbol();
EmitLabel(Start);
StringRef UniqueName = Name.str() + "." + itostr(MappingSymbolCounter++);
MCSymbol *Symbol = getContext().GetOrCreateSymbol(UniqueName);
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
MCELF::SetType(SD, ELF::STT_NOTYPE);
MCELF::SetBinding(SD, ELF::STB_LOCAL);
SD.setExternal(false);
Symbol->setSection(*getCurrentSection());
const MCExpr *Value = MCSymbolRefExpr::Create(Start, getContext());
Symbol->setVariableValue(Value);
}
void EmitThumbFunc(MCSymbol *Func) {
// FIXME: Anything needed here to flag the function as thumb?
getAssembler().setIsThumbFunc(Func);
MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Func);
SD.setFlags(SD.getFlags() | ELF_Other_ThumbFunc);
}
bool IsThumb;
int64_t MappingSymbolCounter;
DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
ElfMappingSymbol LastEMS;
/// @}
};
}
namespace llvm {
MCELFStreamer* createARMELFStreamer(MCContext &Context, MCAsmBackend &TAB,
raw_ostream &OS, MCCodeEmitter *Emitter,
bool RelaxAll, bool NoExecStack,
bool IsThumb) {
ARMELFStreamer *S = new ARMELFStreamer(Context, TAB, OS, Emitter, IsThumb);
if (RelaxAll)
S->getAssembler().setRelaxAll(true);
if (NoExecStack)
S->getAssembler().setNoExecStack(true);
return S;
}
}
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