llvm/lib/MC/MCSFrame.cpp

//===- lib/MC/MCSFrame.cpp - MCSFrame implementation ----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCSFrame.h"
#include "llvm/BinaryFormat/SFrame.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectStreamer.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/EndianStream.h"

using namespace llvm;
using namespace sframe;

namespace {

// Emitting these field-by-field, instead of constructing the actual structures
// lets Streamer do target endian-fixups for free.

class SFrameEmitterImpl {
  MCObjectStreamer &Streamer;
  ABI SFrameABI;
  MCSymbol *FDESubSectionStart;
  MCSymbol *FRESubSectionStart;
  MCSymbol *FRESubSectionEnd;

public:
  SFrameEmitterImpl(MCObjectStreamer &Streamer) : Streamer(Streamer) {
    assert(Streamer.getContext()
               .getObjectFileInfo()
               ->getSFrameABIArch()
               .has_value());
    SFrameABI = *Streamer.getContext().getObjectFileInfo()->getSFrameABIArch();
    FDESubSectionStart = Streamer.getContext().createTempSymbol();
    FRESubSectionStart = Streamer.getContext().createTempSymbol();
    FRESubSectionEnd = Streamer.getContext().createTempSymbol();
  }

  void emitPreamble() {
    Streamer.emitInt16(Magic);
    Streamer.emitInt8(static_cast<uint8_t>(Version::V2));
    Streamer.emitInt8(0);
  }

  void emitHeader() {
    emitPreamble();
    // sfh_abi_arch
    Streamer.emitInt8(static_cast<uint8_t>(SFrameABI));
    // sfh_cfa_fixed_fp_offset
    Streamer.emitInt8(0);
    // sfh_cfa_fixed_ra_offset
    Streamer.emitInt8(0);
    // sfh_auxhdr_len
    Streamer.emitInt8(0);
    // shf_num_fdes
    Streamer.emitInt32(0);
    // shf_num_fres
    Streamer.emitInt32(0);
    // shf_fre_len
    Streamer.emitAbsoluteSymbolDiff(FRESubSectionEnd, FRESubSectionStart,
                                    sizeof(int32_t));
    // shf_fdeoff. With no sfh_auxhdr, these immediately follow this header.
    Streamer.emitInt32(0);
    // shf_freoff
    Streamer.emitAbsoluteSymbolDiff(FRESubSectionStart, FDESubSectionStart,
                                    sizeof(uint32_t));
  }

  void emitFDEs() { Streamer.emitLabel(FDESubSectionStart); }

  void emitFREs() {
    Streamer.emitLabel(FRESubSectionStart);
    Streamer.emitLabel(FRESubSectionEnd);
  }
};

} // end anonymous namespace

void MCSFrameEmitter::emit(MCObjectStreamer &Streamer) {
  MCContext &Context = Streamer.getContext();
  SFrameEmitterImpl Emitter(Streamer);

  MCSection *Section = Context.getObjectFileInfo()->getSFrameSection();
  // Not strictly necessary, but gas always aligns to 8, so match that.
  Section->ensureMinAlignment(Align(8));
  Streamer.switchSection(Section);
  MCSymbol *SectionStart = Context.createTempSymbol();
  Streamer.emitLabel(SectionStart);
  Emitter.emitHeader();
  Emitter.emitFDEs();
  Emitter.emitFREs();
}