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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "MCTargetDesc/BPFMCTargetDesc.h" 10 #include "llvm/ADT/StringRef.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 20 using namespace llvm; 21 22 namespace { 23 24 class BPFAsmBackend : public MCAsmBackend { 25 public: 26 BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {} 27 ~BPFAsmBackend() override = default; 28 29 void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 30 const MCValue &Target, MutableArrayRef<char> Data, 31 uint64_t Value, bool IsResolved, 32 const MCSubtargetInfo *STI) const override; 33 34 std::unique_ptr<MCObjectTargetWriter> 35 createObjectTargetWriter() const override; 36 37 // No instruction requires relaxation 38 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value, 39 const MCRelaxableFragment *DF, 40 const MCAsmLayout &Layout) const override { 41 return false; 42 } 43 44 unsigned getNumFixupKinds() const override { return 1; } 45 46 bool mayNeedRelaxation(const MCInst &Inst, 47 const MCSubtargetInfo &STI) const override { 48 return false; 49 } 50 51 void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI, 52 MCInst &Res) const override {} 53 54 bool writeNopData(raw_ostream &OS, uint64_t Count) const override; 55 }; 56 57 } // end anonymous namespace 58 59 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const { 60 if ((Count % 8) != 0) 61 return false; 62 63 for (uint64_t i = 0; i < Count; i += 8) 64 support::endian::write<uint64_t>(OS, 0x15000000, Endian); 65 66 return true; 67 } 68 69 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 70 const MCValue &Target, 71 MutableArrayRef<char> Data, uint64_t Value, 72 bool IsResolved, 73 const MCSubtargetInfo *STI) const { 74 if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) { 75 // The Value is 0 for global variables, and the in-section offset 76 // for static variables. Write to the immediate field of the inst. 77 assert(Value <= UINT32_MAX); 78 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], 79 static_cast<uint32_t>(Value), 80 Endian); 81 } else if (Fixup.getKind() == FK_Data_4) { 82 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian); 83 } else if (Fixup.getKind() == FK_Data_8) { 84 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian); 85 } else if (Fixup.getKind() == FK_PCRel_4) { 86 Value = (uint32_t)((Value - 8) / 8); 87 if (Endian == support::little) { 88 Data[Fixup.getOffset() + 1] = 0x10; 89 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value); 90 } else { 91 Data[Fixup.getOffset() + 1] = 0x1; 92 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value); 93 } 94 } else { 95 assert(Fixup.getKind() == FK_PCRel_2); 96 Value = (uint16_t)((Value - 8) / 8); 97 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value, 98 Endian); 99 } 100 } 101 102 std::unique_ptr<MCObjectTargetWriter> 103 BPFAsmBackend::createObjectTargetWriter() const { 104 return createBPFELFObjectWriter(0); 105 } 106 107 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T, 108 const MCSubtargetInfo &STI, 109 const MCRegisterInfo &MRI, 110 const MCTargetOptions &) { 111 return new BPFAsmBackend(support::little); 112 } 113 114 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T, 115 const MCSubtargetInfo &STI, 116 const MCRegisterInfo &MRI, 117 const MCTargetOptions &) { 118 return new BPFAsmBackend(support::big); 119 } 120