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//===-- BPFELFObjectWriter.cpp - BPF ELF Writer ---------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/BPFMCTargetDesc.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/ErrorHandling.h"
#include <cstdint>
using namespace llvm;
namespace {
class BPFELFObjectWriter : public MCELFObjectTargetWriter {
public:
BPFELFObjectWriter(uint8_t OSABI);
~BPFELFObjectWriter() override = default;
protected:
unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
const MCFixup &Fixup, bool IsPCRel) const override;
};
} // end anonymous namespace
BPFELFObjectWriter::BPFELFObjectWriter(uint8_t OSABI)
: MCELFObjectTargetWriter(/*Is64Bit*/ true, OSABI, ELF::EM_BPF,
/*HasRelocationAddend*/ false) {}
unsigned BPFELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
const MCFixup &Fixup,
bool IsPCRel) const {
// determine the type of the relocation
switch (Fixup.getKind()) {
default:
llvm_unreachable("invalid fixup kind!");
case FK_SecRel_8:
// LD_imm64 instruction.
return ELF::R_BPF_64_64;
case FK_PCRel_4:
// CALL instruction.
return ELF::R_BPF_64_32;
case FK_Data_8:
return ELF::R_BPF_64_ABS64;
case FK_Data_4:
if (const MCSymbolRefExpr *A = Target.getSymA()) {
const MCSymbol &Sym = A->getSymbol();
if (Sym.isDefined()) {
MCSection &Section = Sym.getSection();
const MCSectionELF *SectionELF = dyn_cast<MCSectionELF>(&Section);
assert(SectionELF && "Null section for reloc symbol");
unsigned Flags = SectionELF->getFlags();
if (Sym.isTemporary()) {
// .BTF.ext generates FK_Data_4 relocations for
// insn offset by creating temporary labels.
// The reloc symbol should be in text section.
// Use a different relocation to instruct ExecutionEngine
// RuntimeDyld not to do relocation for it, yet still to
// allow lld to do proper adjustment when merging sections.
if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))
return ELF::R_BPF_64_NODYLD32;
} else {
// .BTF generates FK_Data_4 relocations for variable
// offset in DataSec kind.
// The reloc symbol should be in data section.
if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_WRITE))
return ELF::R_BPF_64_NODYLD32;
}
}
}
return ELF::R_BPF_64_ABS32;
}
}
std::unique_ptr<MCObjectTargetWriter>
llvm::createBPFELFObjectWriter(uint8_t OSABI) {
return std::make_unique<BPFELFObjectWriter>(OSABI);
}
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