1 //===- BPFDisassembler.cpp - Disassembler for BPF ---------------*- C++ -*-===//
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 is part of the BPF Disassembler.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "MCTargetDesc/BPFMCTargetDesc.h"
14 #include "TargetInfo/BPFTargetInfo.h"
15 #include "llvm/ADT/ArrayRef.h"
16 #include "llvm/MC/MCAsmInfo.h"
17 #include "llvm/MC/MCContext.h"
18 #include "llvm/MC/MCDisassembler/MCDisassembler.h"
19 #include "llvm/MC/MCFixedLenDisassembler.h"
20 #include "llvm/MC/MCInst.h"
21 #include "llvm/Support/MathExtras.h"
22 #include "llvm/Support/TargetRegistry.h"
23 #include <cstdint>
24 
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "bpf-disassembler"
28 
29 typedef MCDisassembler::DecodeStatus DecodeStatus;
30 
31 namespace {
32 
33 /// A disassembler class for BPF.
34 class BPFDisassembler : public MCDisassembler {
35 public:
36   enum BPF_CLASS {
37     BPF_LD = 0x0,
38     BPF_LDX = 0x1,
39     BPF_ST = 0x2,
40     BPF_STX = 0x3,
41     BPF_ALU = 0x4,
42     BPF_JMP = 0x5,
43     BPF_JMP32 = 0x6,
44     BPF_ALU64 = 0x7
45   };
46 
47   enum BPF_SIZE {
48     BPF_W = 0x0,
49     BPF_H = 0x1,
50     BPF_B = 0x2,
51     BPF_DW = 0x3
52   };
53 
54   enum BPF_MODE {
55     BPF_IMM = 0x0,
56     BPF_ABS = 0x1,
57     BPF_IND = 0x2,
58     BPF_MEM = 0x3,
59     BPF_LEN = 0x4,
60     BPF_MSH = 0x5,
61     BPF_ATOMIC = 0x6
62   };
63 
64   BPFDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx)
65       : MCDisassembler(STI, Ctx) {}
66   ~BPFDisassembler() override = default;
67 
68   DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
69                               ArrayRef<uint8_t> Bytes, uint64_t Address,
70                               raw_ostream &CStream) const override;
71 
72   uint8_t getInstClass(uint64_t Inst) const { return (Inst >> 56) & 0x7; };
73   uint8_t getInstSize(uint64_t Inst) const { return (Inst >> 59) & 0x3; };
74   uint8_t getInstMode(uint64_t Inst) const { return (Inst >> 61) & 0x7; };
75 };
76 
77 } // end anonymous namespace
78 
79 static MCDisassembler *createBPFDisassembler(const Target &T,
80                                              const MCSubtargetInfo &STI,
81                                              MCContext &Ctx) {
82   return new BPFDisassembler(STI, Ctx);
83 }
84 
85 
86 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeBPFDisassembler() {
87   // Register the disassembler.
88   TargetRegistry::RegisterMCDisassembler(getTheBPFTarget(),
89                                          createBPFDisassembler);
90   TargetRegistry::RegisterMCDisassembler(getTheBPFleTarget(),
91                                          createBPFDisassembler);
92   TargetRegistry::RegisterMCDisassembler(getTheBPFbeTarget(),
93                                          createBPFDisassembler);
94 }
95 
96 static const unsigned GPRDecoderTable[] = {
97     BPF::R0,  BPF::R1,  BPF::R2,  BPF::R3,  BPF::R4,  BPF::R5,
98     BPF::R6,  BPF::R7,  BPF::R8,  BPF::R9,  BPF::R10, BPF::R11};
99 
100 static DecodeStatus DecodeGPRRegisterClass(MCInst &Inst, unsigned RegNo,
101                                            uint64_t /*Address*/,
102                                            const void * /*Decoder*/) {
103   if (RegNo > 11)
104     return MCDisassembler::Fail;
105 
106   unsigned Reg = GPRDecoderTable[RegNo];
107   Inst.addOperand(MCOperand::createReg(Reg));
108   return MCDisassembler::Success;
109 }
110 
111 static const unsigned GPR32DecoderTable[] = {
112     BPF::W0,  BPF::W1,  BPF::W2,  BPF::W3,  BPF::W4,  BPF::W5,
113     BPF::W6,  BPF::W7,  BPF::W8,  BPF::W9,  BPF::W10, BPF::W11};
114 
115 static DecodeStatus DecodeGPR32RegisterClass(MCInst &Inst, unsigned RegNo,
116                                              uint64_t /*Address*/,
117                                              const void * /*Decoder*/) {
118   if (RegNo > 11)
119     return MCDisassembler::Fail;
120 
121   unsigned Reg = GPR32DecoderTable[RegNo];
122   Inst.addOperand(MCOperand::createReg(Reg));
123   return MCDisassembler::Success;
124 }
125 
126 static DecodeStatus decodeMemoryOpValue(MCInst &Inst, unsigned Insn,
127                                         uint64_t Address, const void *Decoder) {
128   unsigned Register = (Insn >> 16) & 0xf;
129   if (Register > 11)
130     return MCDisassembler::Fail;
131 
132   Inst.addOperand(MCOperand::createReg(GPRDecoderTable[Register]));
133   unsigned Offset = (Insn & 0xffff);
134   Inst.addOperand(MCOperand::createImm(SignExtend32<16>(Offset)));
135 
136   return MCDisassembler::Success;
137 }
138 
139 #include "BPFGenDisassemblerTables.inc"
140 static DecodeStatus readInstruction64(ArrayRef<uint8_t> Bytes, uint64_t Address,
141                                       uint64_t &Size, uint64_t &Insn,
142                                       bool IsLittleEndian) {
143   uint64_t Lo, Hi;
144 
145   if (Bytes.size() < 8) {
146     Size = 0;
147     return MCDisassembler::Fail;
148   }
149 
150   Size = 8;
151   if (IsLittleEndian) {
152     Hi = (Bytes[0] << 24) | (Bytes[1] << 16) | (Bytes[2] << 0) | (Bytes[3] << 8);
153     Lo = (Bytes[4] << 0) | (Bytes[5] << 8) | (Bytes[6] << 16) | (Bytes[7] << 24);
154   } else {
155     Hi = (Bytes[0] << 24) | ((Bytes[1] & 0x0F) << 20) | ((Bytes[1] & 0xF0) << 12) |
156          (Bytes[2] << 8) | (Bytes[3] << 0);
157     Lo = (Bytes[4] << 24) | (Bytes[5] << 16) | (Bytes[6] << 8) | (Bytes[7] << 0);
158   }
159   Insn = Make_64(Hi, Lo);
160 
161   return MCDisassembler::Success;
162 }
163 
164 DecodeStatus BPFDisassembler::getInstruction(MCInst &Instr, uint64_t &Size,
165                                              ArrayRef<uint8_t> Bytes,
166                                              uint64_t Address,
167                                              raw_ostream &CStream) const {
168   bool IsLittleEndian = getContext().getAsmInfo()->isLittleEndian();
169   uint64_t Insn, Hi;
170   DecodeStatus Result;
171 
172   Result = readInstruction64(Bytes, Address, Size, Insn, IsLittleEndian);
173   if (Result == MCDisassembler::Fail) return MCDisassembler::Fail;
174 
175   uint8_t InstClass = getInstClass(Insn);
176   uint8_t InstMode = getInstMode(Insn);
177   if ((InstClass == BPF_LDX || InstClass == BPF_STX) &&
178       getInstSize(Insn) != BPF_DW &&
179       (InstMode == BPF_MEM || InstMode == BPF_ATOMIC) &&
180       STI.getFeatureBits()[BPF::ALU32])
181     Result = decodeInstruction(DecoderTableBPFALU3264, Instr, Insn, Address,
182                                this, STI);
183   else
184     Result = decodeInstruction(DecoderTableBPF64, Instr, Insn, Address, this,
185                                STI);
186 
187   if (Result == MCDisassembler::Fail) return MCDisassembler::Fail;
188 
189   switch (Instr.getOpcode()) {
190   case BPF::LD_imm64:
191   case BPF::LD_pseudo: {
192     if (Bytes.size() < 16) {
193       Size = 0;
194       return MCDisassembler::Fail;
195     }
196     Size = 16;
197     if (IsLittleEndian)
198       Hi = (Bytes[12] << 0) | (Bytes[13] << 8) | (Bytes[14] << 16) | (Bytes[15] << 24);
199     else
200       Hi = (Bytes[12] << 24) | (Bytes[13] << 16) | (Bytes[14] << 8) | (Bytes[15] << 0);
201     auto& Op = Instr.getOperand(1);
202     Op.setImm(Make_64(Hi, Op.getImm()));
203     break;
204   }
205   case BPF::LD_ABS_B:
206   case BPF::LD_ABS_H:
207   case BPF::LD_ABS_W:
208   case BPF::LD_IND_B:
209   case BPF::LD_IND_H:
210   case BPF::LD_IND_W: {
211     auto Op = Instr.getOperand(0);
212     Instr.clear();
213     Instr.addOperand(MCOperand::createReg(BPF::R6));
214     Instr.addOperand(Op);
215     break;
216   }
217   }
218 
219   return Result;
220 }
221 
222 typedef DecodeStatus (*DecodeFunc)(MCInst &MI, unsigned insn, uint64_t Address,
223                                    const void *Decoder);
224