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//===- 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/MCAsmInfo.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 {
// High-level structure to track info needed to emit a sframe_func_desc_entry
// and its associated FREs.
struct SFrameFDE {
// Reference to the original dwarf frame to avoid copying.
const MCDwarfFrameInfo &DFrame;
// Label where this FDE's FREs start.
MCSymbol *FREStart;
SFrameFDE(const MCDwarfFrameInfo &DF, MCSymbol *FRES)
: DFrame(DF), FREStart(FRES) {}
void emit(MCObjectStreamer &S, const MCSymbol *FRESubSectionStart) {
MCContext &C = S.getContext();
// sfde_func_start_address
const MCExpr *V = C.getAsmInfo()->getExprForFDESymbol(
&(*DFrame.Begin), C.getObjectFileInfo()->getFDEEncoding(), S);
S.emitValue(V, sizeof(int32_t));
// sfde_func_size
S.emitAbsoluteSymbolDiff(DFrame.End, DFrame.Begin, sizeof(uint32_t));
// sfde_func_start_fre_off
auto *F = S.getCurrentFragment();
const MCExpr *Diff = MCBinaryExpr::createSub(
MCSymbolRefExpr::create(FREStart, C),
MCSymbolRefExpr::create(FRESubSectionStart, C), C);
F->addFixup(MCFixup::create(F->getContents().size(), Diff,
MCFixup::getDataKindForSize(4)));
S.emitInt32(0);
// sfde_func_start_num_fres
S.emitInt32(0);
// sfde_func_info word
FDEInfo<endianness::native> I;
I.setFuncInfo(0 /* No pauth key */, FDEType::PCInc, FREType::Addr1);
S.emitInt8(I.Info);
// sfde_func_rep_size. Not relevant in non-PCMASK fdes.
S.emitInt8(0);
// sfde_func_padding2
S.emitInt16(0);
}
};
// Emitting these field-by-field, instead of constructing the actual structures
// lets Streamer do target endian-fixups for free.
class SFrameEmitterImpl {
MCObjectStreamer &Streamer;
SmallVector<SFrameFDE> FDEs;
ABI SFrameABI;
MCSymbol *FDESubSectionStart;
MCSymbol *FRESubSectionStart;
MCSymbol *FRESubSectionEnd;
public:
SFrameEmitterImpl(MCObjectStreamer &Streamer) : Streamer(Streamer) {
assert(Streamer.getContext()
.getObjectFileInfo()
->getSFrameABIArch()
.has_value());
FDEs.reserve(Streamer.getDwarfFrameInfos().size());
SFrameABI = *Streamer.getContext().getObjectFileInfo()->getSFrameABIArch();
FDESubSectionStart = Streamer.getContext().createTempSymbol();
FRESubSectionStart = Streamer.getContext().createTempSymbol();
FRESubSectionEnd = Streamer.getContext().createTempSymbol();
}
void BuildSFDE(const MCDwarfFrameInfo &DF) {
FDEs.emplace_back(DF, Streamer.getContext().createTempSymbol());
}
void emitPreamble() {
Streamer.emitInt16(Magic);
Streamer.emitInt8(static_cast<uint8_t>(Version::V2));
Streamer.emitInt8(static_cast<uint8_t>(Flags::FDEFuncStartPCRel));
}
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(FDEs.size());
// 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);
for (auto &FDE : FDEs) {
FDE.emit(Streamer, FRESubSectionStart);
}
}
void emitFREs() {
Streamer.emitLabel(FRESubSectionStart);
for (auto &FDE : FDEs)
Streamer.emitLabel(FDE.FREStart);
Streamer.emitLabel(FRESubSectionEnd);
}
};
} // end anonymous namespace
void MCSFrameEmitter::emit(MCObjectStreamer &Streamer) {
MCContext &Context = Streamer.getContext();
// If this target doesn't support sframes, return now. Gas doesn't warn in
// this case, but if we want to, it should be done at option-parsing time,
// rather than here.
if (!Streamer.getContext()
.getObjectFileInfo()
->getSFrameABIArch()
.has_value())
return;
SFrameEmitterImpl Emitter(Streamer);
ArrayRef<MCDwarfFrameInfo> FrameArray = Streamer.getDwarfFrameInfos();
// Both the header itself and the FDEs include various offsets and counts.
// Therefore, all of this must be precomputed.
for (const auto &DFrame : FrameArray)
Emitter.BuildSFDE(DFrame);
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();
}
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