1//===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//
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/ADT/StringRef.h"
11#include "llvm/MC/MCAsmBackend.h"
12#include "llvm/MC/MCAssembler.h"
13#include "llvm/MC/MCContext.h"
14#include "llvm/MC/MCFixup.h"
15#include "llvm/MC/MCObjectWriter.h"
16#include "llvm/Support/EndianStream.h"
17#include <cassert>
18#include <cstdint>
19
20using namespace llvm;
21
22namespace {
23
24class BPFAsmBackend : public MCAsmBackend {
25public:
26  BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
27  ~BPFAsmBackend() override = default;
28
29  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
30                  const MCValue &Target, MutableArrayRef<char> Data,
31                  uint64_t Value, bool IsResolved,
32                  const MCSubtargetInfo *STI) const override;
33
34  std::unique_ptr<MCObjectTargetWriter>
35  createObjectTargetWriter() const override;
36
37  // No instruction requires relaxation
38  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
39                            const MCRelaxableFragment *DF,
40                            const MCAsmLayout &Layout) const override {
41    return false;
42  }
43
44  unsigned getNumFixupKinds() const override { return 1; }
45
46  bool mayNeedRelaxation(const MCInst &Inst,
47                         const MCSubtargetInfo &STI) const override {
48    return false;
49  }
50
51  void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
52                        MCInst &Res) const override {}
53
54  bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
55};
56
57} // end anonymous namespace
58
59bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
60  if ((Count % 8) != 0)
61    return false;
62
63  for (uint64_t i = 0; i < Count; i += 8)
64    support::endian::write<uint64_t>(OS, 0x15000000, Endian);
65
66  return true;
67}
68
69void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
70                               const MCValue &Target,
71                               MutableArrayRef<char> Data, uint64_t Value,
72                               bool IsResolved,
73                               const MCSubtargetInfo *STI) const {
74  if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
75    // The Value is 0 for global variables, and the in-section offset
76    // for static variables. Write to the immediate field of the inst.
77    assert(Value <= UINT32_MAX);
78    support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
79                                     static_cast<uint32_t>(Value),
80                                     Endian);
81  } else if (Fixup.getKind() == FK_Data_4) {
82    support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
83  } else if (Fixup.getKind() == FK_Data_8) {
84    support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
85  } else if (Fixup.getKind() == FK_PCRel_4) {
86    Value = (uint32_t)((Value - 8) / 8);
87    if (Endian == support::little) {
88      Data[Fixup.getOffset() + 1] = 0x10;
89      support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
90    } else {
91      Data[Fixup.getOffset() + 1] = 0x1;
92      support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
93    }
94  } else {
95    assert(Fixup.getKind() == FK_PCRel_2);
96    Value = (uint16_t)((Value - 8) / 8);
97    support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
98                                     Endian);
99  }
100}
101
102std::unique_ptr<MCObjectTargetWriter>
103BPFAsmBackend::createObjectTargetWriter() const {
104  return createBPFELFObjectWriter(0);
105}
106
107MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
108                                        const MCSubtargetInfo &STI,
109                                        const MCRegisterInfo &MRI,
110                                        const MCTargetOptions &) {
111  return new BPFAsmBackend(support::little);
112}
113
114MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
115                                          const MCSubtargetInfo &STI,
116                                          const MCRegisterInfo &MRI,
117                                          const MCTargetOptions &) {
118  return new BPFAsmBackend(support::big);
119}
120