1 //===-- BPFMCCodeEmitter.cpp - Convert BPF code to machine code -----------===//
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 // This file implements the BPFMCCodeEmitter class.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "MCTargetDesc/BPFMCTargetDesc.h"
14 #include "llvm/ADT/SmallVector.h"
15 #include "llvm/MC/MCCodeEmitter.h"
16 #include "llvm/MC/MCFixup.h"
17 #include "llvm/MC/MCInst.h"
18 #include "llvm/MC/MCInstrInfo.h"
19 #include "llvm/MC/MCRegisterInfo.h"
20 #include "llvm/MC/MCSubtargetInfo.h"
21 #include "llvm/Support/Endian.h"
22 #include "llvm/Support/EndianStream.h"
23 #include <cassert>
24 #include <cstdint>
25
26 using namespace llvm;
27
28 #define DEBUG_TYPE "mccodeemitter"
29
30 namespace {
31
32 class BPFMCCodeEmitter : public MCCodeEmitter {
33 const MCInstrInfo &MCII;
34 const MCRegisterInfo &MRI;
35 bool IsLittleEndian;
36
37 public:
BPFMCCodeEmitter(const MCInstrInfo & mcii,const MCRegisterInfo & mri,bool IsLittleEndian)38 BPFMCCodeEmitter(const MCInstrInfo &mcii, const MCRegisterInfo &mri,
39 bool IsLittleEndian)
40 : MCII(mcii), MRI(mri), IsLittleEndian(IsLittleEndian) {}
41 BPFMCCodeEmitter(const BPFMCCodeEmitter &) = delete;
42 void operator=(const BPFMCCodeEmitter &) = delete;
43 ~BPFMCCodeEmitter() override = default;
44
45 // getBinaryCodeForInstr - TableGen'erated function for getting the
46 // binary encoding for an instruction.
47 uint64_t getBinaryCodeForInstr(const MCInst &MI,
48 SmallVectorImpl<MCFixup> &Fixups,
49 const MCSubtargetInfo &STI) const;
50
51 // getMachineOpValue - Return binary encoding of operand. If the machin
52 // operand requires relocation, record the relocation and return zero.
53 unsigned getMachineOpValue(const MCInst &MI, const MCOperand &MO,
54 SmallVectorImpl<MCFixup> &Fixups,
55 const MCSubtargetInfo &STI) const;
56
57 uint64_t getMemoryOpValue(const MCInst &MI, unsigned Op,
58 SmallVectorImpl<MCFixup> &Fixups,
59 const MCSubtargetInfo &STI) const;
60
61 void encodeInstruction(const MCInst &MI, raw_ostream &OS,
62 SmallVectorImpl<MCFixup> &Fixups,
63 const MCSubtargetInfo &STI) const override;
64
65 private:
66 FeatureBitset computeAvailableFeatures(const FeatureBitset &FB) const;
67 void
68 verifyInstructionPredicates(const MCInst &MI,
69 const FeatureBitset &AvailableFeatures) const;
70 };
71
72 } // end anonymous namespace
73
createBPFMCCodeEmitter(const MCInstrInfo & MCII,const MCRegisterInfo & MRI,MCContext & Ctx)74 MCCodeEmitter *llvm::createBPFMCCodeEmitter(const MCInstrInfo &MCII,
75 const MCRegisterInfo &MRI,
76 MCContext &Ctx) {
77 return new BPFMCCodeEmitter(MCII, MRI, true);
78 }
79
createBPFbeMCCodeEmitter(const MCInstrInfo & MCII,const MCRegisterInfo & MRI,MCContext & Ctx)80 MCCodeEmitter *llvm::createBPFbeMCCodeEmitter(const MCInstrInfo &MCII,
81 const MCRegisterInfo &MRI,
82 MCContext &Ctx) {
83 return new BPFMCCodeEmitter(MCII, MRI, false);
84 }
85
getMachineOpValue(const MCInst & MI,const MCOperand & MO,SmallVectorImpl<MCFixup> & Fixups,const MCSubtargetInfo & STI) const86 unsigned BPFMCCodeEmitter::getMachineOpValue(const MCInst &MI,
87 const MCOperand &MO,
88 SmallVectorImpl<MCFixup> &Fixups,
89 const MCSubtargetInfo &STI) const {
90 if (MO.isReg())
91 return MRI.getEncodingValue(MO.getReg());
92 if (MO.isImm())
93 return static_cast<unsigned>(MO.getImm());
94
95 assert(MO.isExpr());
96
97 const MCExpr *Expr = MO.getExpr();
98
99 assert(Expr->getKind() == MCExpr::SymbolRef);
100
101 if (MI.getOpcode() == BPF::JAL)
102 // func call name
103 Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_4));
104 else if (MI.getOpcode() == BPF::LD_imm64)
105 Fixups.push_back(MCFixup::create(0, Expr, FK_SecRel_8));
106 else
107 // bb label
108 Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_2));
109
110 return 0;
111 }
112
SwapBits(uint8_t Val)113 static uint8_t SwapBits(uint8_t Val)
114 {
115 return (Val & 0x0F) << 4 | (Val & 0xF0) >> 4;
116 }
117
encodeInstruction(const MCInst & MI,raw_ostream & OS,SmallVectorImpl<MCFixup> & Fixups,const MCSubtargetInfo & STI) const118 void BPFMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
119 SmallVectorImpl<MCFixup> &Fixups,
120 const MCSubtargetInfo &STI) const {
121 verifyInstructionPredicates(MI,
122 computeAvailableFeatures(STI.getFeatureBits()));
123
124 unsigned Opcode = MI.getOpcode();
125 support::endian::Writer OSE(OS,
126 IsLittleEndian ? support::little : support::big);
127
128 if (Opcode == BPF::LD_imm64 || Opcode == BPF::LD_pseudo) {
129 uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
130 OS << char(Value >> 56);
131 if (IsLittleEndian)
132 OS << char((Value >> 48) & 0xff);
133 else
134 OS << char(SwapBits((Value >> 48) & 0xff));
135 OSE.write<uint16_t>(0);
136 OSE.write<uint32_t>(Value & 0xffffFFFF);
137
138 const MCOperand &MO = MI.getOperand(1);
139 uint64_t Imm = MO.isImm() ? MO.getImm() : 0;
140 OSE.write<uint8_t>(0);
141 OSE.write<uint8_t>(0);
142 OSE.write<uint16_t>(0);
143 OSE.write<uint32_t>(Imm >> 32);
144 } else {
145 // Get instruction encoding and emit it
146 uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
147 OS << char(Value >> 56);
148 if (IsLittleEndian)
149 OS << char((Value >> 48) & 0xff);
150 else
151 OS << char(SwapBits((Value >> 48) & 0xff));
152 OSE.write<uint16_t>((Value >> 32) & 0xffff);
153 OSE.write<uint32_t>(Value & 0xffffFFFF);
154 }
155 }
156
157 // Encode BPF Memory Operand
getMemoryOpValue(const MCInst & MI,unsigned Op,SmallVectorImpl<MCFixup> & Fixups,const MCSubtargetInfo & STI) const158 uint64_t BPFMCCodeEmitter::getMemoryOpValue(const MCInst &MI, unsigned Op,
159 SmallVectorImpl<MCFixup> &Fixups,
160 const MCSubtargetInfo &STI) const {
161 uint64_t Encoding;
162 const MCOperand Op1 = MI.getOperand(1);
163 assert(Op1.isReg() && "First operand is not register.");
164 Encoding = MRI.getEncodingValue(Op1.getReg());
165 Encoding <<= 16;
166 MCOperand Op2 = MI.getOperand(2);
167 assert(Op2.isImm() && "Second operand is not immediate.");
168 Encoding |= Op2.getImm() & 0xffff;
169 return Encoding;
170 }
171
172 #define ENABLE_INSTR_PREDICATE_VERIFIER
173 #include "BPFGenMCCodeEmitter.inc"
174