1 //===-- BPFELFObjectWriter.cpp - BPF ELF Writer ---------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9
10 #include "MCTargetDesc/BPFMCTargetDesc.h"
11 #include "llvm/BinaryFormat/ELF.h"
12 #include "llvm/MC/MCELFObjectWriter.h"
13 #include "llvm/MC/MCFixup.h"
14 #include "llvm/MC/MCObjectWriter.h"
15 #include "llvm/MC/MCValue.h"
16 #include "llvm/Support/ErrorHandling.h"
17 #include <cstdint>
18
19 using namespace llvm;
20
21 namespace {
22
23 class BPFELFObjectWriter : public MCELFObjectTargetWriter {
24 public:
25 BPFELFObjectWriter(uint8_t OSABI);
26 ~BPFELFObjectWriter() override = default;
27
28 protected:
29 unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
30 const MCFixup &Fixup, bool IsPCRel) const override;
31 };
32
33 } // end anonymous namespace
34
BPFELFObjectWriter(uint8_t OSABI)35 BPFELFObjectWriter::BPFELFObjectWriter(uint8_t OSABI)
36 : MCELFObjectTargetWriter(/*Is64Bit*/ true, OSABI, ELF::EM_BPF,
37 /*HasRelocationAddend*/ false) {}
38
getRelocType(MCContext & Ctx,const MCValue & Target,const MCFixup & Fixup,bool IsPCRel) const39 unsigned BPFELFObjectWriter::getRelocType(MCContext &Ctx, const MCValue &Target,
40 const MCFixup &Fixup,
41 bool IsPCRel) const {
42 // determine the type of the relocation
43 switch ((unsigned)Fixup.getKind()) {
44 default:
45 llvm_unreachable("invalid fixup kind!");
46 case FK_SecRel_8:
47 return ELF::R_BPF_64_64;
48 case FK_PCRel_4:
49 case FK_SecRel_4:
50 return ELF::R_BPF_64_32;
51 case FK_Data_8:
52 return ELF::R_BPF_64_64;
53 case FK_Data_4:
54 // .BTF.ext generates FK_Data_4 relocations for
55 // insn offset by creating temporary labels.
56 // The insn offset is within the code section and
57 // already been fulfilled by applyFixup(). No
58 // further relocation is needed.
59 if (const MCSymbolRefExpr *A = Target.getSymA()) {
60 if (A->getSymbol().isTemporary()) {
61 MCSection &Section = A->getSymbol().getSection();
62 const MCSectionELF *SectionELF = dyn_cast<MCSectionELF>(&Section);
63 assert(SectionELF && "Null section for reloc symbol");
64
65 // The reloc symbol should be in text section.
66 unsigned Flags = SectionELF->getFlags();
67 if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))
68 return ELF::R_BPF_NONE;
69 }
70 }
71 return ELF::R_BPF_64_32;
72 }
73 }
74
75 std::unique_ptr<MCObjectTargetWriter>
createBPFELFObjectWriter(uint8_t OSABI)76 llvm::createBPFELFObjectWriter(uint8_t OSABI) {
77 return llvm::make_unique<BPFELFObjectWriter>(OSABI);
78 }
79