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/BPFMCFixups.h"
10#include "MCTargetDesc/BPFMCTargetDesc.h"
11#include "llvm/ADT/StringRef.h"
12#include "llvm/MC/MCAsmBackend.h"
13#include "llvm/MC/MCAssembler.h"
14#include "llvm/MC/MCContext.h"
15#include "llvm/MC/MCFixup.h"
16#include "llvm/MC/MCFixupKindInfo.h"
17#include "llvm/MC/MCObjectWriter.h"
18#include "llvm/Support/EndianStream.h"
19#include <cassert>
20#include <cstdint>
21
22using namespace llvm;
23
24namespace {
25
26class BPFAsmBackend : public MCAsmBackend {
27public:
28  BPFAsmBackend(llvm::endianness Endian) : MCAsmBackend(Endian) {}
29  ~BPFAsmBackend() override = default;
30
31  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
32                  const MCValue &Target, MutableArrayRef<char> Data,
33                  uint64_t Value, bool IsResolved,
34                  const MCSubtargetInfo *STI) const override;
35
36  std::unique_ptr<MCObjectTargetWriter>
37  createObjectTargetWriter() const override;
38
39  // No instruction requires relaxation
40  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
41                            const MCRelaxableFragment *DF,
42                            const MCAsmLayout &Layout) const override {
43    return false;
44  }
45
46  unsigned getNumFixupKinds() const override {
47    return BPF::NumTargetFixupKinds;
48  }
49  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
50
51  bool writeNopData(raw_ostream &OS, uint64_t Count,
52                    const MCSubtargetInfo *STI) const override;
53};
54
55} // end anonymous namespace
56
57const MCFixupKindInfo &
58BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
59  const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = {
60    { "FK_BPF_PCRel_4",  0, 32, MCFixupKindInfo::FKF_IsPCRel },
61  };
62
63  if (Kind < FirstTargetFixupKind)
64    return MCAsmBackend::getFixupKindInfo(Kind);
65
66  assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
67         "Invalid kind!");
68  return Infos[Kind - FirstTargetFixupKind];
69}
70
71bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
72                                 const MCSubtargetInfo *STI) const {
73  if ((Count % 8) != 0)
74    return false;
75
76  for (uint64_t i = 0; i < Count; i += 8)
77    support::endian::write<uint64_t>(OS, 0x15000000, Endian);
78
79  return true;
80}
81
82void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
83                               const MCValue &Target,
84                               MutableArrayRef<char> Data, uint64_t Value,
85                               bool IsResolved,
86                               const MCSubtargetInfo *STI) const {
87  if (Fixup.getKind() == FK_SecRel_8) {
88    // The Value is 0 for global variables, and the in-section offset
89    // for static variables. Write to the immediate field of the inst.
90    assert(Value <= UINT32_MAX);
91    support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
92                                     static_cast<uint32_t>(Value),
93                                     Endian);
94  } else if (Fixup.getKind() == FK_Data_4) {
95    support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
96  } else if (Fixup.getKind() == FK_Data_8) {
97    support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
98  } else if (Fixup.getKind() == FK_PCRel_4) {
99    Value = (uint32_t)((Value - 8) / 8);
100    if (Endian == llvm::endianness::little) {
101      Data[Fixup.getOffset() + 1] = 0x10;
102      support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
103    } else {
104      Data[Fixup.getOffset() + 1] = 0x1;
105      support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
106    }
107  } else if (Fixup.getTargetKind() == BPF::FK_BPF_PCRel_4) {
108    // The input Value represents the number of bytes.
109    Value = (uint32_t)((Value - 8) / 8);
110    support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], Value,
111                                     Endian);
112  } else {
113    assert(Fixup.getKind() == FK_PCRel_2);
114
115    int64_t ByteOff = (int64_t)Value - 8;
116    if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8)
117      report_fatal_error("Branch target out of insn range");
118
119    Value = (uint16_t)((Value - 8) / 8);
120    support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
121                                     Endian);
122  }
123}
124
125std::unique_ptr<MCObjectTargetWriter>
126BPFAsmBackend::createObjectTargetWriter() const {
127  return createBPFELFObjectWriter(0);
128}
129
130MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
131                                        const MCSubtargetInfo &STI,
132                                        const MCRegisterInfo &MRI,
133                                        const MCTargetOptions &) {
134  return new BPFAsmBackend(llvm::endianness::little);
135}
136
137MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
138                                          const MCSubtargetInfo &STI,
139                                          const MCRegisterInfo &MRI,
140                                          const MCTargetOptions &) {
141  return new BPFAsmBackend(llvm::endianness::big);
142}
143