124 lines · cpp
1//===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "MCTargetDesc/BPFMCFixups.h"10#include "MCTargetDesc/BPFMCTargetDesc.h"11#include "llvm/MC/MCAsmBackend.h"12#include "llvm/MC/MCAssembler.h"13#include "llvm/MC/MCContext.h"14#include "llvm/MC/MCFixup.h"15#include "llvm/MC/MCObjectWriter.h"16#include "llvm/Support/EndianStream.h"17#include <cassert>18#include <cstdint>19 20using namespace llvm;21 22namespace {23 24class BPFAsmBackend : public MCAsmBackend {25public:26 BPFAsmBackend(llvm::endianness Endian) : MCAsmBackend(Endian) {}27 ~BPFAsmBackend() override = default;28 29 void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target,30 uint8_t *Data, uint64_t Value, bool IsResolved) override;31 32 std::unique_ptr<MCObjectTargetWriter>33 createObjectTargetWriter() const override;34 35 MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const override;36 37 bool writeNopData(raw_ostream &OS, uint64_t Count,38 const MCSubtargetInfo *STI) const override;39};40 41} // end anonymous namespace42 43MCFixupKindInfo BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {44 const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = {45 {"FK_BPF_PCRel_4", 0, 32, 0},46 };47 48 if (Kind < FirstTargetFixupKind)49 return MCAsmBackend::getFixupKindInfo(Kind);50 51 assert(unsigned(Kind - FirstTargetFixupKind) < BPF::NumTargetFixupKinds &&52 "Invalid kind!");53 return Infos[Kind - FirstTargetFixupKind];54}55 56bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,57 const MCSubtargetInfo *STI) const {58 if ((Count % 8) != 0)59 return false;60 61 for (uint64_t i = 0; i < Count; i += 8)62 support::endian::write<uint64_t>(OS, 0x15000000, Endian);63 64 return true;65}66 67void BPFAsmBackend::applyFixup(const MCFragment &F, const MCFixup &Fixup,68 const MCValue &Target, uint8_t *Data,69 uint64_t Value, bool IsResolved) {70 maybeAddReloc(F, Fixup, Target, Value, IsResolved);71 if (Fixup.getKind() == FK_SecRel_8) {72 // The Value is 0 for global variables, and the in-section offset73 // for static variables. Write to the immediate field of the inst.74 assert(Value <= UINT32_MAX);75 support::endian::write<uint32_t>(Data + 4, static_cast<uint32_t>(Value),76 Endian);77 } else if (Fixup.getKind() == FK_Data_4 && !Fixup.isPCRel()) {78 support::endian::write<uint32_t>(Data, Value, Endian);79 } else if (Fixup.getKind() == FK_Data_8) {80 support::endian::write<uint64_t>(Data, Value, Endian);81 } else if (Fixup.getKind() == FK_Data_4 && Fixup.isPCRel()) {82 Value = (uint32_t)((Value - 8) / 8);83 if (Endian == llvm::endianness::little) {84 Data[1] = 0x10;85 support::endian::write32le(Data + 4, Value);86 } else {87 Data[1] = 0x1;88 support::endian::write32be(Data + 4, Value);89 }90 } else if (Fixup.getKind() == BPF::FK_BPF_PCRel_4) {91 // The input Value represents the number of bytes.92 Value = (uint32_t)((Value - 8) / 8);93 support::endian::write<uint32_t>(Data + 4, Value, Endian);94 } else {95 assert(Fixup.getKind() == FK_Data_2 && Fixup.isPCRel());96 97 int64_t ByteOff = (int64_t)Value - 8;98 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8)99 report_fatal_error("Branch target out of insn range");100 101 Value = (uint16_t)((Value - 8) / 8);102 support::endian::write<uint16_t>(Data + 2, Value, Endian);103 }104}105 106std::unique_ptr<MCObjectTargetWriter>107BPFAsmBackend::createObjectTargetWriter() const {108 return createBPFELFObjectWriter(0);109}110 111MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,112 const MCSubtargetInfo &STI,113 const MCRegisterInfo &MRI,114 const MCTargetOptions &) {115 return new BPFAsmBackend(llvm::endianness::little);116}117 118MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,119 const MCSubtargetInfo &STI,120 const MCRegisterInfo &MRI,121 const MCTargetOptions &) {122 return new BPFAsmBackend(llvm::endianness::big);123}124