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/ADT/StringRef.h"
12 #include "llvm/MC/MCAsmBackend.h"
13 #include "llvm/MC/MCFixup.h"
14 #include "llvm/MC/MCObjectWriter.h"
15 #include <cassert>
16 #include <cstdint>
17 
18 using namespace llvm;
19 
20 namespace {
21 
22 class BPFAsmBackend : public MCAsmBackend {
23 public:
24   bool IsLittleEndian;
25 
26   BPFAsmBackend(bool IsLittleEndian)
27     : MCAsmBackend(), IsLittleEndian(IsLittleEndian) {}
28   ~BPFAsmBackend() override = default;
29 
30   void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
31                   uint64_t Value, bool IsPCRel) const override;
32 
33   MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override;
34 
35   // No instruction requires relaxation
36   bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
37                             const MCRelaxableFragment *DF,
38                             const MCAsmLayout &Layout) const override {
39     return false;
40   }
41 
42   unsigned getNumFixupKinds() const override { return 1; }
43 
44   bool mayNeedRelaxation(const MCInst &Inst) const override { return false; }
45 
46   void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
47                         MCInst &Res) const override {}
48 
49   bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override;
50 };
51 
52 } // end anonymous namespace
53 
54 bool BPFAsmBackend::writeNopData(uint64_t Count, MCObjectWriter *OW) const {
55   if ((Count % 8) != 0)
56     return false;
57 
58   for (uint64_t i = 0; i < Count; i += 8)
59     OW->write64(0x15000000);
60 
61   return true;
62 }
63 
64 void BPFAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
65                                unsigned DataSize, uint64_t Value,
66                                bool IsPCRel) const {
67   if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
68     assert(Value == 0);
69   } else if (Fixup.getKind() == FK_Data_4 || Fixup.getKind() == FK_Data_8) {
70     unsigned Size = Fixup.getKind() == FK_Data_4 ? 4 : 8;
71 
72     for (unsigned i = 0; i != Size; ++i) {
73       unsigned Idx = IsLittleEndian ? i : Size - i;
74       Data[Fixup.getOffset() + Idx] = uint8_t(Value >> (i * 8));
75     }
76   } else {
77     assert(Fixup.getKind() == FK_PCRel_2);
78     Value = (uint16_t)((Value - 8) / 8);
79     if (IsLittleEndian) {
80       Data[Fixup.getOffset() + 2] = Value & 0xFF;
81       Data[Fixup.getOffset() + 3] = Value >> 8;
82     } else {
83       Data[Fixup.getOffset() + 2] = Value >> 8;
84       Data[Fixup.getOffset() + 3] = Value & 0xFF;
85     }
86   }
87 }
88 
89 MCObjectWriter *BPFAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const {
90   return createBPFELFObjectWriter(OS, 0, IsLittleEndian);
91 }
92 
93 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
94                                         const MCRegisterInfo &MRI,
95                                         const Triple &TT, StringRef CPU,
96                                         const MCTargetOptions&) {
97   return new BPFAsmBackend(/*IsLittleEndian=*/true);
98 }
99 
100 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
101                                           const MCRegisterInfo &MRI,
102                                           const Triple &TT, StringRef CPU,
103                                           const MCTargetOptions&) {
104   return new BPFAsmBackend(/*IsLittleEndian=*/false);
105 }
106