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/BPFMCTargetDesc.h"
10 #include "llvm/ADT/StringRef.h"
11 #include "llvm/MC/MCAsmBackend.h"
12 #include "llvm/MC/MCAssembler.h"
13 #include "llvm/MC/MCContext.h"
14 #include "llvm/MC/MCFixup.h"
15 #include "llvm/MC/MCObjectWriter.h"
16 #include "llvm/Support/EndianStream.h"
17 #include <cassert>
18 #include <cstdint>
19
20 using namespace llvm;
21
22 namespace {
23
24 class BPFAsmBackend : public MCAsmBackend {
25 public:
BPFAsmBackend(support::endianness Endian)26 BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
27 ~BPFAsmBackend() override = default;
28
29 void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
30 const MCValue &Target, MutableArrayRef<char> Data,
31 uint64_t Value, bool IsResolved,
32 const MCSubtargetInfo *STI) const override;
33
34 std::unique_ptr<MCObjectTargetWriter>
35 createObjectTargetWriter() const override;
36
37 // No instruction requires relaxation
fixupNeedsRelaxation(const MCFixup & Fixup,uint64_t Value,const MCRelaxableFragment * DF,const MCAsmLayout & Layout) const38 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
39 const MCRelaxableFragment *DF,
40 const MCAsmLayout &Layout) const override {
41 return false;
42 }
43
getNumFixupKinds() const44 unsigned getNumFixupKinds() const override { return 1; }
45
mayNeedRelaxation(const MCInst & Inst,const MCSubtargetInfo & STI) const46 bool mayNeedRelaxation(const MCInst &Inst,
47 const MCSubtargetInfo &STI) const override {
48 return false;
49 }
50
51 bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
52 };
53
54 } // end anonymous namespace
55
writeNopData(raw_ostream & OS,uint64_t Count) const56 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
57 if ((Count % 8) != 0)
58 return false;
59
60 for (uint64_t i = 0; i < Count; i += 8)
61 support::endian::write<uint64_t>(OS, 0x15000000, Endian);
62
63 return true;
64 }
65
applyFixup(const MCAssembler & Asm,const MCFixup & Fixup,const MCValue & Target,MutableArrayRef<char> Data,uint64_t Value,bool IsResolved,const MCSubtargetInfo * STI) const66 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
67 const MCValue &Target,
68 MutableArrayRef<char> Data, uint64_t Value,
69 bool IsResolved,
70 const MCSubtargetInfo *STI) const {
71 if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
72 // The Value is 0 for global variables, and the in-section offset
73 // for static variables. Write to the immediate field of the inst.
74 assert(Value <= UINT32_MAX);
75 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
76 static_cast<uint32_t>(Value),
77 Endian);
78 } else if (Fixup.getKind() == FK_Data_4) {
79 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
80 } else if (Fixup.getKind() == FK_Data_8) {
81 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
82 } else if (Fixup.getKind() == FK_PCRel_4) {
83 Value = (uint32_t)((Value - 8) / 8);
84 if (Endian == support::little) {
85 Data[Fixup.getOffset() + 1] = 0x10;
86 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
87 } else {
88 Data[Fixup.getOffset() + 1] = 0x1;
89 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
90 }
91 } else {
92 assert(Fixup.getKind() == FK_PCRel_2);
93 Value = (uint16_t)((Value - 8) / 8);
94 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
95 Endian);
96 }
97 }
98
99 std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const100 BPFAsmBackend::createObjectTargetWriter() const {
101 return createBPFELFObjectWriter(0);
102 }
103
createBPFAsmBackend(const Target & T,const MCSubtargetInfo & STI,const MCRegisterInfo & MRI,const MCTargetOptions &)104 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
105 const MCSubtargetInfo &STI,
106 const MCRegisterInfo &MRI,
107 const MCTargetOptions &) {
108 return new BPFAsmBackend(support::little);
109 }
110
createBPFbeAsmBackend(const Target & T,const MCSubtargetInfo & STI,const MCRegisterInfo & MRI,const MCTargetOptions &)111 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
112 const MCSubtargetInfo &STI,
113 const MCRegisterInfo &MRI,
114 const MCTargetOptions &) {
115 return new BPFAsmBackend(support::big);
116 }
117