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 // No instruction requires relaxation 40 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value, 41 const MCRelaxableFragment *DF, 42 const MCAsmLayout &Layout) const override { 43 return false; 44 } 45 46 unsigned getNumFixupKinds() const override { 47 return BPF::NumTargetFixupKinds; 48 } 49 const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override; 50 51 bool writeNopData(raw_ostream &OS, uint64_t Count, 52 const MCSubtargetInfo *STI) const override; 53 }; 54 55 } // end anonymous namespace 56 57 const MCFixupKindInfo & 58 BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const { 59 const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = { 60 { "FK_BPF_PCRel_4", 0, 32, MCFixupKindInfo::FKF_IsPCRel }, 61 }; 62 63 if (Kind < FirstTargetFixupKind) 64 return MCAsmBackend::getFixupKindInfo(Kind); 65 66 assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() && 67 "Invalid kind!"); 68 return Infos[Kind - FirstTargetFixupKind]; 69 } 70 71 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count, 72 const MCSubtargetInfo *STI) const { 73 if ((Count % 8) != 0) 74 return false; 75 76 for (uint64_t i = 0; i < Count; i += 8) 77 support::endian::write<uint64_t>(OS, 0x15000000, Endian); 78 79 return true; 80 } 81 82 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 83 const MCValue &Target, 84 MutableArrayRef<char> Data, uint64_t Value, 85 bool IsResolved, 86 const MCSubtargetInfo *STI) const { 87 if (Fixup.getKind() == FK_SecRel_8) { 88 // The Value is 0 for global variables, and the in-section offset 89 // for static variables. Write to the immediate field of the inst. 90 assert(Value <= UINT32_MAX); 91 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], 92 static_cast<uint32_t>(Value), 93 Endian); 94 } else if (Fixup.getKind() == FK_Data_4) { 95 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian); 96 } else if (Fixup.getKind() == FK_Data_8) { 97 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian); 98 } else if (Fixup.getKind() == FK_PCRel_4) { 99 Value = (uint32_t)((Value - 8) / 8); 100 if (Endian == llvm::endianness::little) { 101 Data[Fixup.getOffset() + 1] = 0x10; 102 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value); 103 } else { 104 Data[Fixup.getOffset() + 1] = 0x1; 105 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value); 106 } 107 } else if (Fixup.getTargetKind() == BPF::FK_BPF_PCRel_4) { 108 // The input Value represents the number of bytes. 109 Value = (uint32_t)((Value - 8) / 8); 110 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], Value, 111 Endian); 112 } else { 113 assert(Fixup.getKind() == FK_PCRel_2); 114 115 int64_t ByteOff = (int64_t)Value - 8; 116 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8) 117 report_fatal_error("Branch target out of insn range"); 118 119 Value = (uint16_t)((Value - 8) / 8); 120 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value, 121 Endian); 122 } 123 } 124 125 std::unique_ptr<MCObjectTargetWriter> 126 BPFAsmBackend::createObjectTargetWriter() const { 127 return createBPFELFObjectWriter(0); 128 } 129 130 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T, 131 const MCSubtargetInfo &STI, 132 const MCRegisterInfo &MRI, 133 const MCTargetOptions &) { 134 return new BPFAsmBackend(llvm::endianness::little); 135 } 136 137 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T, 138 const MCSubtargetInfo &STI, 139 const MCRegisterInfo &MRI, 140 const MCTargetOptions &) { 141 return new BPFAsmBackend(llvm::endianness::big); 142 } 143