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/ADT/StringRef.h" 12 #include "llvm/MC/MCAsmBackend.h" 13 #include "llvm/MC/MCAssembler.h" 14 #include "llvm/MC/MCContext.h" 15 #include "llvm/MC/MCFixup.h" 16 #include "llvm/MC/MCFixupKindInfo.h" 17 #include "llvm/MC/MCObjectWriter.h" 18 #include "llvm/Support/EndianStream.h" 19 #include <cassert> 20 #include <cstdint> 21 22 using namespace llvm; 23 24 namespace { 25 26 class BPFAsmBackend : public MCAsmBackend { 27 public: 28 BPFAsmBackend(llvm::endianness Endian) : MCAsmBackend(Endian) {} 29 ~BPFAsmBackend() override = default; 30 31 void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 32 const MCValue &Target, MutableArrayRef<char> Data, 33 uint64_t Value, bool IsResolved, 34 const MCSubtargetInfo *STI) const override; 35 36 std::unique_ptr<MCObjectTargetWriter> 37 createObjectTargetWriter() const override; 38 39 unsigned getNumFixupKinds() const override { 40 return BPF::NumTargetFixupKinds; 41 } 42 const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override; 43 44 bool writeNopData(raw_ostream &OS, uint64_t Count, 45 const MCSubtargetInfo *STI) const override; 46 }; 47 48 } // end anonymous namespace 49 50 const MCFixupKindInfo & 51 BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const { 52 const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = { 53 { "FK_BPF_PCRel_4", 0, 32, MCFixupKindInfo::FKF_IsPCRel }, 54 }; 55 56 if (Kind < FirstTargetFixupKind) 57 return MCAsmBackend::getFixupKindInfo(Kind); 58 59 assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() && 60 "Invalid kind!"); 61 return Infos[Kind - FirstTargetFixupKind]; 62 } 63 64 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count, 65 const MCSubtargetInfo *STI) const { 66 if ((Count % 8) != 0) 67 return false; 68 69 for (uint64_t i = 0; i < Count; i += 8) 70 support::endian::write<uint64_t>(OS, 0x15000000, Endian); 71 72 return true; 73 } 74 75 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 76 const MCValue &Target, 77 MutableArrayRef<char> Data, uint64_t Value, 78 bool IsResolved, 79 const MCSubtargetInfo *STI) const { 80 if (Fixup.getKind() == FK_SecRel_8) { 81 // The Value is 0 for global variables, and the in-section offset 82 // for static variables. Write to the immediate field of the inst. 83 assert(Value <= UINT32_MAX); 84 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], 85 static_cast<uint32_t>(Value), 86 Endian); 87 } else if (Fixup.getKind() == FK_Data_4) { 88 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian); 89 } else if (Fixup.getKind() == FK_Data_8) { 90 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian); 91 } else if (Fixup.getKind() == FK_PCRel_4) { 92 Value = (uint32_t)((Value - 8) / 8); 93 if (Endian == llvm::endianness::little) { 94 Data[Fixup.getOffset() + 1] = 0x10; 95 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value); 96 } else { 97 Data[Fixup.getOffset() + 1] = 0x1; 98 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value); 99 } 100 } else if (Fixup.getTargetKind() == BPF::FK_BPF_PCRel_4) { 101 // The input Value represents the number of bytes. 102 Value = (uint32_t)((Value - 8) / 8); 103 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], Value, 104 Endian); 105 } else { 106 assert(Fixup.getKind() == FK_PCRel_2); 107 108 int64_t ByteOff = (int64_t)Value - 8; 109 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8) 110 report_fatal_error("Branch target out of insn range"); 111 112 Value = (uint16_t)((Value - 8) / 8); 113 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value, 114 Endian); 115 } 116 } 117 118 std::unique_ptr<MCObjectTargetWriter> 119 BPFAsmBackend::createObjectTargetWriter() const { 120 return createBPFELFObjectWriter(0); 121 } 122 123 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T, 124 const MCSubtargetInfo &STI, 125 const MCRegisterInfo &MRI, 126 const MCTargetOptions &) { 127 return new BPFAsmBackend(llvm::endianness::little); 128 } 129 130 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T, 131 const MCSubtargetInfo &STI, 132 const MCRegisterInfo &MRI, 133 const MCTargetOptions &) { 134 return new BPFAsmBackend(llvm::endianness::big); 135 } 136