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 
23 using namespace llvm;
24 
25 namespace {
26 class BPFAsmBackend : public MCAsmBackend {
27 public:
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 
55 bool 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 
65 void 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     return;
72   }
73   assert(Fixup.getKind() == FK_PCRel_2);
74   Value = (uint16_t)((Value - 8) / 8);
75   if (IsLittleEndian) {
76     Data[Fixup.getOffset() + 2] = Value & 0xFF;
77     Data[Fixup.getOffset() + 3] = Value >> 8;
78   } else {
79     Data[Fixup.getOffset() + 2] = Value >> 8;
80     Data[Fixup.getOffset() + 3] = Value & 0xFF;
81   }
82 }
83 
84 MCObjectWriter *BPFAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const {
85   return createBPFELFObjectWriter(OS, 0, IsLittleEndian);
86 }
87 }
88 
89 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
90                                         const MCRegisterInfo &MRI,
91                                         const Triple &TT, StringRef CPU) {
92   return new BPFAsmBackend(/*IsLittleEndian=*/true);
93 }
94 
95 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
96                                           const MCRegisterInfo &MRI,
97                                           const Triple &TT, StringRef CPU) {
98   return new BPFAsmBackend(/*IsLittleEndian=*/false);
99 }
100