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/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 20 using namespace llvm; 21 22 namespace { 23 24 class BPFAsmBackend : public MCAsmBackend { 25 public: 26 BPFAsmBackend(llvm::endianness Endian) : MCAsmBackend(Endian) {} 27 ~BPFAsmBackend() override = default; 28 29 void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target, 30 MutableArrayRef<char> Data, uint64_t Value, 31 bool IsResolved) override; 32 33 std::unique_ptr<MCObjectTargetWriter> 34 createObjectTargetWriter() const override; 35 36 MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const override; 37 38 bool writeNopData(raw_ostream &OS, uint64_t Count, 39 const MCSubtargetInfo *STI) const override; 40 }; 41 42 } // end anonymous namespace 43 44 MCFixupKindInfo BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const { 45 const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = { 46 {"FK_BPF_PCRel_4", 0, 32, 0}, 47 }; 48 49 if (Kind < FirstTargetFixupKind) 50 return MCAsmBackend::getFixupKindInfo(Kind); 51 52 assert(unsigned(Kind - FirstTargetFixupKind) < BPF::NumTargetFixupKinds && 53 "Invalid kind!"); 54 return Infos[Kind - FirstTargetFixupKind]; 55 } 56 57 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count, 58 const MCSubtargetInfo *STI) const { 59 if ((Count % 8) != 0) 60 return false; 61 62 for (uint64_t i = 0; i < Count; i += 8) 63 support::endian::write<uint64_t>(OS, 0x15000000, Endian); 64 65 return true; 66 } 67 68 void BPFAsmBackend::applyFixup(const MCFragment &F, const MCFixup &Fixup, 69 const MCValue &Target, 70 MutableArrayRef<char> Data, uint64_t Value, 71 bool IsResolved) { 72 maybeAddReloc(F, Fixup, Target, Value, IsResolved); 73 if (Fixup.getKind() == FK_SecRel_8) { 74 // The Value is 0 for global variables, and the in-section offset 75 // for static variables. Write to the immediate field of the inst. 76 assert(Value <= UINT32_MAX); 77 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], 78 static_cast<uint32_t>(Value), 79 Endian); 80 } else if (Fixup.getKind() == FK_Data_4 && !Fixup.isPCRel()) { 81 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian); 82 } else if (Fixup.getKind() == FK_Data_8) { 83 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian); 84 } else if (Fixup.getKind() == FK_Data_4 && Fixup.isPCRel()) { 85 Value = (uint32_t)((Value - 8) / 8); 86 if (Endian == llvm::endianness::little) { 87 Data[Fixup.getOffset() + 1] = 0x10; 88 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value); 89 } else { 90 Data[Fixup.getOffset() + 1] = 0x1; 91 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value); 92 } 93 } else if (Fixup.getKind() == BPF::FK_BPF_PCRel_4) { 94 // The input Value represents the number of bytes. 95 Value = (uint32_t)((Value - 8) / 8); 96 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], Value, 97 Endian); 98 } else { 99 assert(Fixup.getKind() == FK_Data_2 && Fixup.isPCRel()); 100 101 int64_t ByteOff = (int64_t)Value - 8; 102 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8) 103 report_fatal_error("Branch target out of insn range"); 104 105 Value = (uint16_t)((Value - 8) / 8); 106 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value, 107 Endian); 108 } 109 } 110 111 std::unique_ptr<MCObjectTargetWriter> 112 BPFAsmBackend::createObjectTargetWriter() const { 113 return createBPFELFObjectWriter(0); 114 } 115 116 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T, 117 const MCSubtargetInfo &STI, 118 const MCRegisterInfo &MRI, 119 const MCTargetOptions &) { 120 return new BPFAsmBackend(llvm::endianness::little); 121 } 122 123 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T, 124 const MCSubtargetInfo &STI, 125 const MCRegisterInfo &MRI, 126 const MCTargetOptions &) { 127 return new BPFAsmBackend(llvm::endianness::big); 128 } 129