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//===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//
//
// 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 "MCTargetDesc/BPFMCTargetDesc.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/Support/EndianStream.h"
#include <cassert>
#include <cstdint>
using namespace llvm;
namespace {
class BPFAsmBackend : public MCAsmBackend {
public:
BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
~BPFAsmBackend() override = default;
void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
const MCValue &Target, MutableArrayRef<char> Data,
uint64_t Value, bool IsResolved,
const MCSubtargetInfo *STI) const override;
std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const override;
// No instruction requires relaxation
bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
const MCRelaxableFragment *DF,
const MCAsmLayout &Layout) const override {
return false;
}
unsigned getNumFixupKinds() const override { return 1; }
bool mayNeedRelaxation(const MCInst &Inst,
const MCSubtargetInfo &STI) const override {
return false;
}
void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
MCInst &Res) const override {}
bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
};
} // end anonymous namespace
bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
if ((Count % 8) != 0)
return false;
for (uint64_t i = 0; i < Count; i += 8)
support::endian::write<uint64_t>(OS, 0x15000000, Endian);
return true;
}
void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
const MCValue &Target,
MutableArrayRef<char> Data, uint64_t Value,
bool IsResolved,
const MCSubtargetInfo *STI) const {
if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
// The Value is 0 for global variables, and the in-section offset
// for static variables. Write to the immediate field of the inst.
assert(Value <= UINT32_MAX);
support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
static_cast<uint32_t>(Value),
Endian);
} else if (Fixup.getKind() == FK_Data_4) {
support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
} else if (Fixup.getKind() == FK_Data_8) {
support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
} else if (Fixup.getKind() == FK_PCRel_4) {
Value = (uint32_t)((Value - 8) / 8);
if (Endian == support::little) {
Data[Fixup.getOffset() + 1] = 0x10;
support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
} else {
Data[Fixup.getOffset() + 1] = 0x1;
support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
}
} else {
assert(Fixup.getKind() == FK_PCRel_2);
Value = (uint16_t)((Value - 8) / 8);
support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
Endian);
}
}
std::unique_ptr<MCObjectTargetWriter>
BPFAsmBackend::createObjectTargetWriter() const {
return createBPFELFObjectWriter(0);
}
MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
const MCSubtargetInfo &STI,
const MCRegisterInfo &MRI,
const MCTargetOptions &) {
return new BPFAsmBackend(support::little);
}
MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
const MCSubtargetInfo &STI,
const MCRegisterInfo &MRI,
const MCTargetOptions &) {
return new BPFAsmBackend(support::big);
}
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