1 //===-- BPFELFObjectWriter.cpp - BPF ELF Writer ---------------------------===// 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/BinaryFormat/ELF.h" 11 #include "llvm/MC/MCELFObjectWriter.h" 12 #include "llvm/MC/MCFixup.h" 13 #include "llvm/MC/MCObjectWriter.h" 14 #include "llvm/MC/MCValue.h" 15 #include "llvm/Support/ErrorHandling.h" 16 #include <cstdint> 17 18 using namespace llvm; 19 20 namespace { 21 22 class BPFELFObjectWriter : public MCELFObjectTargetWriter { 23 public: 24 BPFELFObjectWriter(uint8_t OSABI); 25 ~BPFELFObjectWriter() override = default; 26 27 protected: 28 unsigned getRelocType(const MCFixup &, const MCValue &, 29 bool IsPCRel) const override; 30 }; 31 32 } // end anonymous namespace 33 34 BPFELFObjectWriter::BPFELFObjectWriter(uint8_t OSABI) 35 : MCELFObjectTargetWriter(/*Is64Bit*/ true, OSABI, ELF::EM_BPF, 36 /*HasRelocationAddend*/ false) {} 37 38 unsigned BPFELFObjectWriter::getRelocType(const MCFixup &Fixup, 39 const MCValue &Target, 40 bool IsPCRel) const { 41 // determine the type of the relocation 42 switch (Fixup.getKind()) { 43 default: 44 llvm_unreachable("invalid fixup kind!"); 45 case FK_SecRel_8: 46 // LD_imm64 instruction. 47 return ELF::R_BPF_64_64; 48 case FK_Data_8: 49 return ELF::R_BPF_64_ABS64; 50 case FK_Data_4: 51 if (Fixup.isPCRel()) // CALL instruction 52 return ELF::R_BPF_64_32; 53 if (const auto *A = Target.getAddSym()) { 54 const MCSymbol &Sym = *A; 55 56 if (Sym.isDefined()) { 57 MCSection &Section = Sym.getSection(); 58 const MCSectionELF *SectionELF = dyn_cast<MCSectionELF>(&Section); 59 assert(SectionELF && "Null section for reloc symbol"); 60 61 unsigned Flags = SectionELF->getFlags(); 62 63 if (Sym.isTemporary()) { 64 // .BTF.ext generates FK_Data_4 relocations for 65 // insn offset by creating temporary labels. 66 // The reloc symbol should be in text section. 67 // Use a different relocation to instruct ExecutionEngine 68 // RuntimeDyld not to do relocation for it, yet still to 69 // allow lld to do proper adjustment when merging sections. 70 if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR)) 71 return ELF::R_BPF_64_NODYLD32; 72 } else { 73 // .BTF generates FK_Data_4 relocations for variable 74 // offset in DataSec kind. 75 // The reloc symbol should be in data section. 76 if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_WRITE)) 77 return ELF::R_BPF_64_NODYLD32; 78 } 79 } 80 } 81 return ELF::R_BPF_64_ABS32; 82 } 83 } 84 85 std::unique_ptr<MCObjectTargetWriter> 86 llvm::createBPFELFObjectWriter(uint8_t OSABI) { 87 return std::make_unique<BPFELFObjectWriter>(OSABI); 88 } 89