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
46 bool writeNopData(raw_ostream &OS, uint64_t Count,
47 const MCSubtargetInfo *STI) const override;
48 };
49
50 } // end anonymous namespace
51
writeNopData(raw_ostream & OS,uint64_t Count,const MCSubtargetInfo * STI) const52 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
53 const MCSubtargetInfo *STI) const {
54 if ((Count % 8) != 0)
55 return false;
56
57 for (uint64_t i = 0; i < Count; i += 8)
58 support::endian::write<uint64_t>(OS, 0x15000000, Endian);
59
60 return true;
61 }
62
applyFixup(const MCAssembler & Asm,const MCFixup & Fixup,const MCValue & Target,MutableArrayRef<char> Data,uint64_t Value,bool IsResolved,const MCSubtargetInfo * STI) const63 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
64 const MCValue &Target,
65 MutableArrayRef<char> Data, uint64_t Value,
66 bool IsResolved,
67 const MCSubtargetInfo *STI) const {
68 if (Fixup.getKind() == FK_SecRel_8) {
69 // The Value is 0 for global variables, and the in-section offset
70 // for static variables. Write to the immediate field of the inst.
71 assert(Value <= UINT32_MAX);
72 support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
73 static_cast<uint32_t>(Value),
74 Endian);
75 } else if (Fixup.getKind() == FK_Data_4) {
76 support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
77 } else if (Fixup.getKind() == FK_Data_8) {
78 support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
79 } else if (Fixup.getKind() == FK_PCRel_4) {
80 Value = (uint32_t)((Value - 8) / 8);
81 if (Endian == support::little) {
82 Data[Fixup.getOffset() + 1] = 0x10;
83 support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
84 } else {
85 Data[Fixup.getOffset() + 1] = 0x1;
86 support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
87 }
88 } else {
89 assert(Fixup.getKind() == FK_PCRel_2);
90
91 int64_t ByteOff = (int64_t)Value - 8;
92 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8)
93 report_fatal_error("Branch target out of insn range");
94
95 Value = (uint16_t)((Value - 8) / 8);
96 support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
97 Endian);
98 }
99 }
100
101 std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const102 BPFAsmBackend::createObjectTargetWriter() const {
103 return createBPFELFObjectWriter(0);
104 }
105
createBPFAsmBackend(const Target & T,const MCSubtargetInfo & STI,const MCRegisterInfo & MRI,const MCTargetOptions &)106 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
107 const MCSubtargetInfo &STI,
108 const MCRegisterInfo &MRI,
109 const MCTargetOptions &) {
110 return new BPFAsmBackend(support::little);
111 }
112
createBPFbeAsmBackend(const Target & T,const MCSubtargetInfo & STI,const MCRegisterInfo & MRI,const MCTargetOptions &)113 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
114 const MCSubtargetInfo &STI,
115 const MCRegisterInfo &MRI,
116 const MCTargetOptions &) {
117 return new BPFAsmBackend(support::big);
118 }
119