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/MCExpr.h"
17 #include "llvm/MC/MCFixup.h"
18 #include "llvm/MC/MCInst.h"
19 #include "llvm/MC/MCInstrInfo.h"
20 #include "llvm/MC/MCRegisterInfo.h"
21 #include "llvm/MC/MCSubtargetInfo.h"
22 #include "llvm/Support/Endian.h"
23 #include "llvm/Support/EndianStream.h"
24 #include <cassert>
25 #include <cstdint>
26
27 using namespace llvm;
28
29 #define DEBUG_TYPE "mccodeemitter"
30
31 namespace {
32
33 class BPFMCCodeEmitter : public MCCodeEmitter {
34 const MCRegisterInfo &MRI;
35 bool IsLittleEndian;
36
37 public:
BPFMCCodeEmitter(const MCInstrInfo &,const MCRegisterInfo & mri,bool IsLittleEndian)38 BPFMCCodeEmitter(const MCInstrInfo &, const MCRegisterInfo &mri,
39 bool IsLittleEndian)
40 : 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
66 } // end anonymous namespace
67
createBPFMCCodeEmitter(const MCInstrInfo & MCII,MCContext & Ctx)68 MCCodeEmitter *llvm::createBPFMCCodeEmitter(const MCInstrInfo &MCII,
69 MCContext &Ctx) {
70 return new BPFMCCodeEmitter(MCII, *Ctx.getRegisterInfo(), true);
71 }
72
createBPFbeMCCodeEmitter(const MCInstrInfo & MCII,MCContext & Ctx)73 MCCodeEmitter *llvm::createBPFbeMCCodeEmitter(const MCInstrInfo &MCII,
74 MCContext &Ctx) {
75 return new BPFMCCodeEmitter(MCII, *Ctx.getRegisterInfo(), false);
76 }
77
getMachineOpValue(const MCInst & MI,const MCOperand & MO,SmallVectorImpl<MCFixup> & Fixups,const MCSubtargetInfo & STI) const78 unsigned BPFMCCodeEmitter::getMachineOpValue(const MCInst &MI,
79 const MCOperand &MO,
80 SmallVectorImpl<MCFixup> &Fixups,
81 const MCSubtargetInfo &STI) const {
82 if (MO.isReg())
83 return MRI.getEncodingValue(MO.getReg());
84 if (MO.isImm())
85 return static_cast<unsigned>(MO.getImm());
86
87 assert(MO.isExpr());
88
89 const MCExpr *Expr = MO.getExpr();
90
91 assert(Expr->getKind() == MCExpr::SymbolRef);
92
93 if (MI.getOpcode() == BPF::JAL)
94 // func call name
95 Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_4));
96 else if (MI.getOpcode() == BPF::LD_imm64)
97 Fixups.push_back(MCFixup::create(0, Expr, FK_SecRel_8));
98 else
99 // bb label
100 Fixups.push_back(MCFixup::create(0, Expr, FK_PCRel_2));
101
102 return 0;
103 }
104
SwapBits(uint8_t Val)105 static uint8_t SwapBits(uint8_t Val)
106 {
107 return (Val & 0x0F) << 4 | (Val & 0xF0) >> 4;
108 }
109
encodeInstruction(const MCInst & MI,raw_ostream & OS,SmallVectorImpl<MCFixup> & Fixups,const MCSubtargetInfo & STI) const110 void BPFMCCodeEmitter::encodeInstruction(const MCInst &MI, raw_ostream &OS,
111 SmallVectorImpl<MCFixup> &Fixups,
112 const MCSubtargetInfo &STI) const {
113 unsigned Opcode = MI.getOpcode();
114 support::endian::Writer OSE(OS,
115 IsLittleEndian ? support::little : support::big);
116
117 if (Opcode == BPF::LD_imm64 || Opcode == BPF::LD_pseudo) {
118 uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
119 OS << char(Value >> 56);
120 if (IsLittleEndian)
121 OS << char((Value >> 48) & 0xff);
122 else
123 OS << char(SwapBits((Value >> 48) & 0xff));
124 OSE.write<uint16_t>(0);
125 OSE.write<uint32_t>(Value & 0xffffFFFF);
126
127 const MCOperand &MO = MI.getOperand(1);
128 uint64_t Imm = MO.isImm() ? MO.getImm() : 0;
129 OSE.write<uint8_t>(0);
130 OSE.write<uint8_t>(0);
131 OSE.write<uint16_t>(0);
132 OSE.write<uint32_t>(Imm >> 32);
133 } else {
134 // Get instruction encoding and emit it
135 uint64_t Value = getBinaryCodeForInstr(MI, Fixups, STI);
136 OS << char(Value >> 56);
137 if (IsLittleEndian)
138 OS << char((Value >> 48) & 0xff);
139 else
140 OS << char(SwapBits((Value >> 48) & 0xff));
141 OSE.write<uint16_t>((Value >> 32) & 0xffff);
142 OSE.write<uint32_t>(Value & 0xffffFFFF);
143 }
144 }
145
146 // Encode BPF Memory Operand
getMemoryOpValue(const MCInst & MI,unsigned Op,SmallVectorImpl<MCFixup> & Fixups,const MCSubtargetInfo & STI) const147 uint64_t BPFMCCodeEmitter::getMemoryOpValue(const MCInst &MI, unsigned Op,
148 SmallVectorImpl<MCFixup> &Fixups,
149 const MCSubtargetInfo &STI) const {
150 // For CMPXCHG instructions, output is implicitly in R0/W0,
151 // so memory operand starts from operand 0.
152 int MemOpStartIndex = 1, Opcode = MI.getOpcode();
153 if (Opcode == BPF::CMPXCHGW32 || Opcode == BPF::CMPXCHGD)
154 MemOpStartIndex = 0;
155
156 uint64_t Encoding;
157 const MCOperand Op1 = MI.getOperand(MemOpStartIndex);
158 assert(Op1.isReg() && "First operand is not register.");
159 Encoding = MRI.getEncodingValue(Op1.getReg());
160 Encoding <<= 16;
161 MCOperand Op2 = MI.getOperand(MemOpStartIndex + 1);
162 assert(Op2.isImm() && "Second operand is not immediate.");
163 Encoding |= Op2.getImm() & 0xffff;
164 return Encoding;
165 }
166
167 #include "BPFGenMCCodeEmitter.inc"
168