e63455d5e0
On some architectures such as Arm and X86 the encoding for a nop may change depending on the subtarget in operation at the time of encoding. This change replaces the per module MCSubtargetInfo retained by the targets AsmBackend in favour of passing through the local MCSubtargetInfo in operation at the time. On Arm using the architectural NOP instruction can have a performance benefit on some implementations. For Arm I've deleted the copy of the AsmBackend's MCSubtargetInfo to limit the chances of this causing problems in the future. I've not done this for other targets such as X86 as there is more frequent use of the MCSubtargetInfo and it looks to be for stable properties that we would not expect to vary per function. This change required threading STI through MCNopsFragment and MCBoundaryAlignFragment. I've attempted to take into account the in tree experimental backends. Differential Revision: https://reviews.llvm.org/D45962
114 lines
4.2 KiB
C++
114 lines
4.2 KiB
C++
//===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "MCTargetDesc/BPFMCTargetDesc.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/MC/MCAsmBackend.h"
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#include "llvm/MC/MCAssembler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCFixup.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/Support/EndianStream.h"
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#include <cassert>
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#include <cstdint>
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using namespace llvm;
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namespace {
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class BPFAsmBackend : public MCAsmBackend {
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public:
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BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
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~BPFAsmBackend() override = default;
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void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
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const MCValue &Target, MutableArrayRef<char> Data,
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uint64_t Value, bool IsResolved,
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const MCSubtargetInfo *STI) const override;
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std::unique_ptr<MCObjectTargetWriter>
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createObjectTargetWriter() const override;
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// No instruction requires relaxation
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bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
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const MCRelaxableFragment *DF,
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const MCAsmLayout &Layout) const override {
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return false;
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}
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unsigned getNumFixupKinds() const override { return 1; }
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bool writeNopData(raw_ostream &OS, uint64_t Count,
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const MCSubtargetInfo *STI) const override;
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};
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} // end anonymous namespace
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bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
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const MCSubtargetInfo *STI) const {
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if ((Count % 8) != 0)
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return false;
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for (uint64_t i = 0; i < Count; i += 8)
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support::endian::write<uint64_t>(OS, 0x15000000, Endian);
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return true;
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}
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void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
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const MCValue &Target,
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MutableArrayRef<char> Data, uint64_t Value,
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bool IsResolved,
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const MCSubtargetInfo *STI) const {
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if (Fixup.getKind() == FK_SecRel_8) {
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// The Value is 0 for global variables, and the in-section offset
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// for static variables. Write to the immediate field of the inst.
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assert(Value <= UINT32_MAX);
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support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
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static_cast<uint32_t>(Value),
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Endian);
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} else if (Fixup.getKind() == FK_Data_4) {
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support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
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} else if (Fixup.getKind() == FK_Data_8) {
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support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
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} else if (Fixup.getKind() == FK_PCRel_4) {
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Value = (uint32_t)((Value - 8) / 8);
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if (Endian == support::little) {
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Data[Fixup.getOffset() + 1] = 0x10;
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support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
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} else {
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Data[Fixup.getOffset() + 1] = 0x1;
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support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
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}
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} else {
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assert(Fixup.getKind() == FK_PCRel_2);
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Value = (uint16_t)((Value - 8) / 8);
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support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
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Endian);
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}
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}
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std::unique_ptr<MCObjectTargetWriter>
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BPFAsmBackend::createObjectTargetWriter() const {
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return createBPFELFObjectWriter(0);
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}
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MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
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const MCSubtargetInfo &STI,
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const MCRegisterInfo &MRI,
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const MCTargetOptions &) {
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return new BPFAsmBackend(support::little);
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}
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MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
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const MCSubtargetInfo &STI,
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const MCRegisterInfo &MRI,
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const MCTargetOptions &) {
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return new BPFAsmBackend(support::big);
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}
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