1//===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//
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/MC/MCAsmBackend.h"
12#include "llvm/MC/MCAssembler.h"
13#include "llvm/MC/MCDirectives.h"
14#include "llvm/MC/MCELFObjectWriter.h"
15#include "llvm/MC/MCFixupKindInfo.h"
16#include "llvm/MC/MCObjectWriter.h"
17#include "llvm/MC/MCSubtargetInfo.h"
18#include "llvm/MC/MCExpr.h"
19#include "llvm/MC/MCSymbol.h"
20#include "llvm/Support/ErrorHandling.h"
21#include "llvm/Support/raw_ostream.h"
22
23using namespace llvm;
24
25namespace {
26class BPFAsmBackend : public MCAsmBackend {
27public:
28  bool IsLittleEndian;
29
30  BPFAsmBackend(bool IsLittleEndian)
31    : MCAsmBackend(), IsLittleEndian(IsLittleEndian) {}
32  ~BPFAsmBackend() override {}
33
34  void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
35                  uint64_t Value, bool IsPCRel) const override;
36
37  MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) 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 { return 1; }
47
48  bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }
49
50  void relaxInstruction(const MCInst &Inst, MCInst &Res) const override {}
51
52  bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override;
53};
54
55bool BPFAsmBackend::writeNopData(uint64_t Count, MCObjectWriter *OW) const {
56  if ((Count % 8) != 0)
57    return false;
58
59  for (uint64_t i = 0; i < Count; i += 8)
60    OW->write64(0x15000000);
61
62  return true;
63}
64
65void BPFAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
66                               unsigned DataSize, uint64_t Value,
67                               bool IsPCRel) const {
68
69  if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
70    assert(Value == 0);
71  } else if (Fixup.getKind() == FK_Data_4 || Fixup.getKind() == FK_Data_8) {
72    unsigned Size = Fixup.getKind() == FK_Data_4 ? 4 : 8;
73
74    for (unsigned i = 0; i != Size; ++i) {
75      unsigned Idx = IsLittleEndian ? i : Size - i;
76      Data[Fixup.getOffset() + Idx] = uint8_t(Value >> (i * 8));
77    }
78  } else {
79    assert(Fixup.getKind() == FK_PCRel_2);
80    Value = (uint16_t)((Value - 8) / 8);
81    if (IsLittleEndian) {
82      Data[Fixup.getOffset() + 2] = Value & 0xFF;
83      Data[Fixup.getOffset() + 3] = Value >> 8;
84    } else {
85      Data[Fixup.getOffset() + 2] = Value >> 8;
86      Data[Fixup.getOffset() + 3] = Value & 0xFF;
87    }
88  }
89}
90
91MCObjectWriter *BPFAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const {
92  return createBPFELFObjectWriter(OS, 0, IsLittleEndian);
93}
94}
95
96MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
97                                        const MCRegisterInfo &MRI,
98                                        const Triple &TT, StringRef CPU) {
99  return new BPFAsmBackend(/*IsLittleEndian=*/true);
100}
101
102MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
103                                          const MCRegisterInfo &MRI,
104                                          const Triple &TT, StringRef CPU) {
105  return new BPFAsmBackend(/*IsLittleEndian=*/false);
106}
107