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/MCAssembler.h"
14 #include "llvm/MC/MCContext.h"
15 #include "llvm/MC/MCFixup.h"
16 #include "llvm/MC/MCObjectWriter.h"
17 #include "llvm/Support/EndianStream.h"
18 #include <cassert>
19 #include <cstdint>
20
21 using namespace llvm;
22
23 namespace {
24
25 class BPFAsmBackend : public MCAsmBackend {
26 public:
BPFAsmBackend(support::endianness Endian)27 BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
28 ~BPFAsmBackend() override = default;
29
30 void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
31 const MCValue &Target, MutableArrayRef<char> Data,
32 uint64_t Value, bool IsResolved,
33 const MCSubtargetInfo *STI) const override;
34
35 std::unique_ptr<MCObjectTargetWriter>
36 createObjectTargetWriter() const override;
37
38 // No instruction requires relaxation
fixupNeedsRelaxation(const MCFixup & Fixup,uint64_t Value,const MCRelaxableFragment * DF,const MCAsmLayout & Layout) const39 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
40 const MCRelaxableFragment *DF,
41 const MCAsmLayout &Layout) const override {
42 return false;
43 }
44
getNumFixupKinds() const45 unsigned getNumFixupKinds() const override { return 1; }
46
mayNeedRelaxation(const MCInst & Inst,const MCSubtargetInfo & STI) const47 bool mayNeedRelaxation(const MCInst &Inst,
48 const MCSubtargetInfo &STI) const override {
49 return false;
50 }
51
relaxInstruction(const MCInst & Inst,const MCSubtargetInfo & STI,MCInst & Res) const52 void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
53 MCInst &Res) const override {}
54
55 bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
56 };
57
58 } // end anonymous namespace
59
writeNopData(raw_ostream & OS,uint64_t Count) const60 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
61 if ((Count % 8) != 0)
62 return false;
63
64 for (uint64_t i = 0; i < Count; i += 8)
65 support::endian::write<uint64_t>(OS, 0x15000000, Endian);
66
67 return true;
68 }
69
applyFixup(const MCAssembler & Asm,const MCFixup & Fixup,const MCValue & Target,MutableArrayRef<char> Data,uint64_t Value,bool IsResolved,const MCSubtargetInfo * STI) const70 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
71 const MCValue &Target,
72 MutableArrayRef<char> Data, uint64_t Value,
73 bool IsResolved,
74 const MCSubtargetInfo *STI) const {
75 if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
76 if (Value) {
77 MCContext &Ctx = Asm.getContext();
78 Ctx.reportError(Fixup.getLoc(),
79 "Unsupported relocation: try to compile with -O2 or above, "
80 "or check your static variable usage");
81 }
82 } else if (Fixup.getKind() == FK_Data_4) {
83 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
84 } else if (Fixup.getKind() == FK_Data_8) {
85 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
86 } else if (Fixup.getKind() == FK_PCRel_4) {
87 Value = (uint32_t)((Value - 8) / 8);
88 if (Endian == support::little) {
89 Data[Fixup.getOffset() + 1] = 0x10;
90 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
91 } else {
92 Data[Fixup.getOffset() + 1] = 0x1;
93 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
94 }
95 } else {
96 assert(Fixup.getKind() == FK_PCRel_2);
97 Value = (uint16_t)((Value - 8) / 8);
98 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
99 Endian);
100 }
101 }
102
103 std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const104 BPFAsmBackend::createObjectTargetWriter() const {
105 return createBPFELFObjectWriter(0);
106 }
107
createBPFAsmBackend(const Target & T,const MCSubtargetInfo & STI,const MCRegisterInfo & MRI,const MCTargetOptions &)108 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
109 const MCSubtargetInfo &STI,
110 const MCRegisterInfo &MRI,
111 const MCTargetOptions &) {
112 return new BPFAsmBackend(support::little);
113 }
114
createBPFbeAsmBackend(const Target & T,const MCSubtargetInfo & STI,const MCRegisterInfo & MRI,const MCTargetOptions &)115 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
116 const MCSubtargetInfo &STI,
117 const MCRegisterInfo &MRI,
118 const MCTargetOptions &) {
119 return new BPFAsmBackend(support::big);
120 }
121