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 ((unsigned)Fixup.getKind()) {
43   default:
44     llvm_unreachable("invalid fixup kind!");
45   case FK_SecRel_8:
46     return ELF::R_BPF_64_64;
47   case FK_PCRel_4:
48   case FK_SecRel_4:
49     return ELF::R_BPF_64_32;
50   case FK_Data_8:
51     return ELF::R_BPF_64_64;
52   case FK_Data_4:
53     // .BTF.ext generates FK_Data_4 relocations for
54     // insn offset by creating temporary labels.
55     // The insn offset is within the code section and
56     // already been fulfilled by applyFixup(). No
57     // further relocation is needed.
58     if (const MCSymbolRefExpr *A = Target.getSymA()) {
59       if (A->getSymbol().isTemporary()) {
60         MCSection &Section = A->getSymbol().getSection();
61         const MCSectionELF *SectionELF = dyn_cast<MCSectionELF>(&Section);
62         assert(SectionELF && "Null section for reloc symbol");
63 
64         // The reloc symbol should be in text section.
65         unsigned Flags = SectionELF->getFlags();
66         if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))
67           return ELF::R_BPF_NONE;
68       }
69     }
70     return ELF::R_BPF_64_32;
71   }
72 }
73 
74 std::unique_ptr<MCObjectTargetWriter>
75 llvm::createBPFELFObjectWriter(uint8_t OSABI) {
76   return llvm::make_unique<BPFELFObjectWriter>(OSABI);
77 }
78