LLVM  14.0.0git
BPFELFObjectWriter.cpp
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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 
10 #include "llvm/BinaryFormat/ELF.h"
12 #include "llvm/MC/MCFixup.h"
13 #include "llvm/MC/MCObjectWriter.h"
14 #include "llvm/MC/MCValue.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 (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_PCRel_4:
49  // CALL instruction.
50  return ELF::R_BPF_64_32;
51  case FK_Data_8:
52  return ELF::R_BPF_64_ABS64;
53  case FK_Data_4:
54  if (const MCSymbolRefExpr *A = Target.getSymA()) {
55  const MCSymbol &Sym = A->getSymbol();
56 
57  if (Sym.isDefined()) {
58  MCSection &Section = Sym.getSection();
59  const MCSectionELF *SectionELF = dyn_cast<MCSectionELF>(&Section);
60  assert(SectionELF && "Null section for reloc symbol");
61 
62  unsigned Flags = SectionELF->getFlags();
63 
64  if (Sym.isTemporary()) {
65  // .BTF.ext generates FK_Data_4 relocations for
66  // insn offset by creating temporary labels.
67  // The reloc symbol should be in text section.
68  // Use a different relocation to instruct ExecutionEngine
69  // RuntimeDyld not to do relocation for it, yet still to
70  // allow lld to do proper adjustment when merging sections.
71  if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_EXECINSTR))
72  return ELF::R_BPF_64_NODYLD32;
73  } else {
74  // .BTF generates FK_Data_4 relocations for variable
75  // offset in DataSec kind.
76  // The reloc symbol should be in data section.
77  if ((Flags & ELF::SHF_ALLOC) && (Flags & ELF::SHF_WRITE))
78  return ELF::R_BPF_64_NODYLD32;
79  }
80  }
81  }
82  return ELF::R_BPF_64_ABS32;
83  }
84 }
85 
86 std::unique_ptr<MCObjectTargetWriter>
88  return std::make_unique<BPFELFObjectWriter>(OSABI);
89 }
BPFMCTargetDesc.h
llvm
This file implements support for optimizing divisions by a constant.
Definition: AllocatorList.h:23
llvm::MCSymbol
MCSymbol - Instances of this class represent a symbol name in the MC file, and MCSymbols are created ...
Definition: MCSymbol.h:41
llvm::MCSymbol::isTemporary
bool isTemporary() const
isTemporary - Check if this is an assembler temporary symbol.
Definition: MCSymbol.h:215
llvm::MCContext
Context object for machine code objects.
Definition: MCContext.h:72
llvm::Target
Target - Wrapper for Target specific information.
Definition: TargetRegistry.h:137
ErrorHandling.h
llvm::MCSymbol::isDefined
bool isDefined() const
isDefined - Check if this symbol is defined (i.e., it has an address).
Definition: MCSymbol.h:243
llvm::createBPFELFObjectWriter
std::unique_ptr< MCObjectTargetWriter > createBPFELFObjectWriter(uint8_t OSABI)
Definition: BPFELFObjectWriter.cpp:87
llvm::MCSectionELF
This represents a section on linux, lots of unix variants and some bare metal systems.
Definition: MCSectionELF.h:28
llvm::ELF::SHF_EXECINSTR
@ SHF_EXECINSTR
Definition: ELF.h:997
llvm::ARMBuildAttrs::Section
@ Section
Legacy Tags.
Definition: ARMBuildAttributes.h:78
llvm::FK_Data_4
@ FK_Data_4
A four-byte fixup.
Definition: MCFixup.h:25
ELF.h
llvm::MCSymbol::getSection
MCSection & getSection() const
Get the section associated with a defined, non-absolute symbol.
Definition: MCSymbol.h:262
false
Definition: StackSlotColoring.cpp:142
llvm::MCELFObjectTargetWriter
Definition: MCELFObjectWriter.h:53
MCELFObjectWriter.h
llvm::ELF::SHF_ALLOC
@ SHF_ALLOC
Definition: ELF.h:994
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
llvm::ELF::EM_BPF
@ EM_BPF
Definition: ELF.h:320
llvm::FK_PCRel_4
@ FK_PCRel_4
A four-byte pc relative fixup.
Definition: MCFixup.h:30
llvm::MCSymbolRefExpr
Represent a reference to a symbol from inside an expression.
Definition: MCExpr.h:192
llvm::MCSectionELF::getFlags
unsigned getFlags() const
Definition: MCSectionELF.h:75
Fixup
PowerPC TLS Dynamic Call Fixup
Definition: PPCTLSDynamicCall.cpp:235
llvm_unreachable
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
Definition: ErrorHandling.h:134
A
* A
Definition: README_ALTIVEC.txt:89
MCFixup.h
llvm::MCSection
Instances of this class represent a uniqued identifier for a section in the current translation unit.
Definition: MCSection.h:39
MCObjectWriter.h
llvm::FK_SecRel_8
@ FK_SecRel_8
A eight-byte section relative fixup.
Definition: MCFixup.h:43
MCValue.h
llvm::FK_Data_8
@ FK_Data_8
A eight-byte fixup.
Definition: MCFixup.h:26
llvm::ELF::SHF_WRITE
@ SHF_WRITE
Definition: ELF.h:991
llvm::MCValue
This represents an "assembler immediate".
Definition: MCValue.h:37
true
basic Basic Alias true
Definition: BasicAliasAnalysis.cpp:1903
llvm::MCFixup
Encode information on a single operation to perform on a byte sequence (e.g., an encoded instruction)...
Definition: MCFixup.h:71