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 writeNopData(raw_ostream &OS, uint64_t Count, 47 const MCSubtargetInfo *STI) const override; 48 }; 49 50 } // end anonymous namespace 51 52 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count, 53 const MCSubtargetInfo *STI) const { 54 if ((Count % 8) != 0) 55 return false; 56 57 for (uint64_t i = 0; i < Count; i += 8) 58 support::endian::write<uint64_t>(OS, 0x15000000, Endian); 59 60 return true; 61 } 62 63 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 64 const MCValue &Target, 65 MutableArrayRef<char> Data, uint64_t Value, 66 bool IsResolved, 67 const MCSubtargetInfo *STI) const { 68 if (Fixup.getKind() == FK_SecRel_8) { 69 // The Value is 0 for global variables, and the in-section offset 70 // for static variables. Write to the immediate field of the inst. 71 assert(Value <= UINT32_MAX); 72 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], 73 static_cast<uint32_t>(Value), 74 Endian); 75 } else if (Fixup.getKind() == FK_Data_4) { 76 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian); 77 } else if (Fixup.getKind() == FK_Data_8) { 78 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian); 79 } else if (Fixup.getKind() == FK_PCRel_4) { 80 Value = (uint32_t)((Value - 8) / 8); 81 if (Endian == support::little) { 82 Data[Fixup.getOffset() + 1] = 0x10; 83 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value); 84 } else { 85 Data[Fixup.getOffset() + 1] = 0x1; 86 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value); 87 } 88 } else { 89 assert(Fixup.getKind() == FK_PCRel_2); 90 91 int64_t ByteOff = (int64_t)Value - 8; 92 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8) 93 report_fatal_error("Branch target out of insn range"); 94 95 Value = (uint16_t)((Value - 8) / 8); 96 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value, 97 Endian); 98 } 99 } 100 101 std::unique_ptr<MCObjectTargetWriter> 102 BPFAsmBackend::createObjectTargetWriter() const { 103 return createBPFELFObjectWriter(0); 104 } 105 106 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T, 107 const MCSubtargetInfo &STI, 108 const MCRegisterInfo &MRI, 109 const MCTargetOptions &) { 110 return new BPFAsmBackend(support::little); 111 } 112 113 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T, 114 const MCSubtargetInfo &STI, 115 const MCRegisterInfo &MRI, 116 const MCTargetOptions &) { 117 return new BPFAsmBackend(support::big); 118 } 119