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
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 namespace
33
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 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 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 for
62 // insn offset by creating temporary labels.
63 // The reloc symbol should be in text section.
64 // Use a different relocation to instruct ExecutionEngine
65 // RuntimeDyld not to do relocation for it, yet still to
66 // 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 variable
71 // 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>(args&: OSABI);
85}
86