llvm/lib/Target/BPF/MCTargetDesc/BPFELFObjectWriter.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-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(MCContext &Ctx, const MCValue &Target,
  29                         const MCFixup &Fixup, 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(MCContext &Ctx, const MCValue &Target,
  39                                           const MCFixup &Fixup,
  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_PCRel_4:
  49     // CALL instruction.
  50     return ELF::R_BPF_64_32;
  51   case FK_Data_8:
  52     return ELF::R_BPF_64_ABS64;
  53   case FK_Data_4:
  54     if (const MCSymbolRefExpr *A = Target.getSymA()) {
  55       const MCSymbol &Sym = A->getSymbol();
  56
  57       if (Sym.isDefined()) {
  58         MCSection &Section = Sym.getSection();
  59         const MCSectionELF *SectionELF = dyn_cast<MCSectionELF>(&Section);
  60         assert(SectionELF && "Null section for reloc symbol");
  61
  62         unsigned Flags = SectionELF->getFlags();
  63
  64         if (Sym.isTemporary()) {
  65           // .BTF.ext generates FK_Data_4 relocations for
  66           // insn offset by creating temporary labels.
  67           // The reloc symbol should be in text section.
  68           // Use a different relocation to instruct ExecutionEngine
  69           // RuntimeDyld not to do relocation for it, yet still to
  70           // allow lld to do proper adjustment when merging sections.
  71           if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))
  72             return ELF::R_BPF_64_NODYLD32;
  73         } else {
  74           // .BTF generates FK_Data_4 relocations for variable
  75           // offset in DataSec kind.
  76           // The reloc symbol should be in data section.
  77           if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_WRITE))
  78             return ELF::R_BPF_64_NODYLD32;
  79         }
  80       }
  81     }
  82     return ELF::R_BPF_64_ABS32;
  83   }
  84 }
  85
  86 std::unique_ptr<MCObjectTargetWriter>
  87 llvm::createBPFELFObjectWriter(uint8_t OSABI) {
  88   return std::make_unique<BPFELFObjectWriter>(OSABI);
  89 }