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 
35 BPFELFObjectWriter::BPFELFObjectWriter(uint8_t OSABI)
36     : MCELFObjectTargetWriter(/*Is64Bit*/ true, OSABI, ELF::EM_BPF,
37                               /*HasRelocationAddend*/ false) {}
38 
39 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>
76 llvm::createBPFELFObjectWriter(uint8_t OSABI) {
77   return llvm::make_unique<BPFELFObjectWriter>(OSABI);
78 }
79