86 lines · cpp
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-exception6//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 18using namespace llvm;19 20namespace {21 22class BPFELFObjectWriter : public MCELFObjectTargetWriter {23public:24 BPFELFObjectWriter(uint8_t OSABI);25 ~BPFELFObjectWriter() override = default;26 27protected:28 unsigned getRelocType(const MCFixup &, const MCValue &,29 bool IsPCRel) const override;30};31 32} // end anonymous namespace33 34BPFELFObjectWriter::BPFELFObjectWriter(uint8_t OSABI)35 : MCELFObjectTargetWriter(/*Is64Bit*/ true, OSABI, ELF::EM_BPF,36 /*HasRelocationAddend*/ false) {}37 38unsigned BPFELFObjectWriter::getRelocType(const MCFixup &Fixup,39 const MCValue &Target,40 bool IsPCRel) const {41 // determine the type of the relocation42 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 instruction52 return ELF::R_BPF_64_32;53 if (const auto *A = Target.getAddSym()) {54 const MCSymbol &Sym = *A;55 56 if (Sym.isDefined()) {57 auto &Section = static_cast<const MCSectionELF &>(Sym.getSection());58 unsigned Flags = Section.getFlags();59 60 if (Sym.isTemporary()) {61 // .BTF.ext generates FK_Data_4 relocations for62 // insn offset by creating temporary labels.63 // The reloc symbol should be in text section.64 // Use a different relocation to instruct ExecutionEngine65 // RuntimeDyld not to do relocation for it, yet still to66 // allow lld to do proper adjustment when merging sections.67 if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))68 return ELF::R_BPF_64_NODYLD32;69 } else {70 // .BTF generates FK_Data_4 relocations for variable71 // offset in DataSec kind.72 // The reloc symbol should be in data section.73 if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_WRITE))74 return ELF::R_BPF_64_NODYLD32;75 }76 }77 }78 return ELF::R_BPF_64_ABS32;79 }80}81 82std::unique_ptr<MCObjectTargetWriter>83llvm::createBPFELFObjectWriter(uint8_t OSABI) {84 return std::make_unique<BPFELFObjectWriter>(OSABI);85}86