1 //==- WebAssemblyDisassembler.cpp - Disassembler for WebAssembly -*- 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 /// \file
10 /// This file is part of the WebAssembly Disassembler.
11 ///
12 /// It contains code to translate the data produced by the decoder into
13 /// MCInsts.
14 ///
15 //===----------------------------------------------------------------------===//
16
17 #include "MCTargetDesc/WebAssemblyMCTypeUtilities.h"
18 #include "TargetInfo/WebAssemblyTargetInfo.h"
19 #include "llvm/MC/MCContext.h"
20 #include "llvm/MC/MCDecoderOps.h"
21 #include "llvm/MC/MCDisassembler/MCDisassembler.h"
22 #include "llvm/MC/MCInst.h"
23 #include "llvm/MC/MCInstrInfo.h"
24 #include "llvm/MC/MCSubtargetInfo.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/MC/MCSymbolWasm.h"
27 #include "llvm/MC/TargetRegistry.h"
28 #include "llvm/Support/Casting.h"
29 #include "llvm/Support/Endian.h"
30 #include "llvm/Support/LEB128.h"
31
32 using namespace llvm;
33
34 #define DEBUG_TYPE "wasm-disassembler"
35
36 using DecodeStatus = MCDisassembler::DecodeStatus;
37
38 #include "WebAssemblyGenDisassemblerTables.inc"
39
40 namespace {
41 static constexpr int WebAssemblyInstructionTableSize = 256;
42
43 class WebAssemblyDisassembler final : public MCDisassembler {
44 std::unique_ptr<const MCInstrInfo> MCII;
45
46 DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
47 ArrayRef<uint8_t> Bytes, uint64_t Address,
48 raw_ostream &CStream) const override;
49 std::optional<DecodeStatus>
50 onSymbolStart(SymbolInfoTy &Symbol, uint64_t &Size, ArrayRef<uint8_t> Bytes,
51 uint64_t Address, raw_ostream &CStream) const override;
52
53 public:
WebAssemblyDisassembler(const MCSubtargetInfo & STI,MCContext & Ctx,std::unique_ptr<const MCInstrInfo> MCII)54 WebAssemblyDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
55 std::unique_ptr<const MCInstrInfo> MCII)
56 : MCDisassembler(STI, Ctx), MCII(std::move(MCII)) {}
57 };
58 } // end anonymous namespace
59
createWebAssemblyDisassembler(const Target & T,const MCSubtargetInfo & STI,MCContext & Ctx)60 static MCDisassembler *createWebAssemblyDisassembler(const Target &T,
61 const MCSubtargetInfo &STI,
62 MCContext &Ctx) {
63 std::unique_ptr<const MCInstrInfo> MCII(T.createMCInstrInfo());
64 return new WebAssemblyDisassembler(STI, Ctx, std::move(MCII));
65 }
66
67 extern "C" LLVM_EXTERNAL_VISIBILITY void
LLVMInitializeWebAssemblyDisassembler()68 LLVMInitializeWebAssemblyDisassembler() {
69 // Register the disassembler for each target.
70 TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(),
71 createWebAssemblyDisassembler);
72 TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget64(),
73 createWebAssemblyDisassembler);
74 }
75
nextByte(ArrayRef<uint8_t> Bytes,uint64_t & Size)76 static int nextByte(ArrayRef<uint8_t> Bytes, uint64_t &Size) {
77 if (Size >= Bytes.size())
78 return -1;
79 auto V = Bytes[Size];
80 Size++;
81 return V;
82 }
83
nextLEB(int64_t & Val,ArrayRef<uint8_t> Bytes,uint64_t & Size,bool Signed)84 static bool nextLEB(int64_t &Val, ArrayRef<uint8_t> Bytes, uint64_t &Size,
85 bool Signed) {
86 unsigned N = 0;
87 const char *Error = nullptr;
88 Val = Signed ? decodeSLEB128(Bytes.data() + Size, &N,
89 Bytes.data() + Bytes.size(), &Error)
90 : static_cast<int64_t>(decodeULEB128(Bytes.data() + Size, &N,
91 Bytes.data() + Bytes.size(),
92 &Error));
93 if (Error)
94 return false;
95 Size += N;
96 return true;
97 }
98
parseLEBImmediate(MCInst & MI,uint64_t & Size,ArrayRef<uint8_t> Bytes,bool Signed)99 static bool parseLEBImmediate(MCInst &MI, uint64_t &Size,
100 ArrayRef<uint8_t> Bytes, bool Signed) {
101 int64_t Val;
102 if (!nextLEB(Val, Bytes, Size, Signed))
103 return false;
104 MI.addOperand(MCOperand::createImm(Val));
105 return true;
106 }
107
108 template <typename T>
parseImmediate(MCInst & MI,uint64_t & Size,ArrayRef<uint8_t> Bytes)109 bool parseImmediate(MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes) {
110 if (Size + sizeof(T) > Bytes.size())
111 return false;
112 T Val =
113 support::endian::read<T, llvm::endianness::little>(Bytes.data() + Size);
114 Size += sizeof(T);
115 if (std::is_floating_point<T>::value) {
116 MI.addOperand(
117 MCOperand::createDFPImm(bit_cast<uint64_t>(static_cast<double>(Val))));
118 } else {
119 MI.addOperand(MCOperand::createImm(static_cast<int64_t>(Val)));
120 }
121 return true;
122 }
123
124 std::optional<MCDisassembler::DecodeStatus>
onSymbolStart(SymbolInfoTy & Symbol,uint64_t & Size,ArrayRef<uint8_t> Bytes,uint64_t Address,raw_ostream & CStream) const125 WebAssemblyDisassembler::onSymbolStart(SymbolInfoTy &Symbol, uint64_t &Size,
126 ArrayRef<uint8_t> Bytes,
127 uint64_t Address,
128 raw_ostream &CStream) const {
129 Size = 0;
130 if (Address == 0) {
131 // Start of a code section: we're parsing only the function count.
132 int64_t FunctionCount;
133 if (!nextLEB(FunctionCount, Bytes, Size, false))
134 return std::nullopt;
135 outs() << " # " << FunctionCount << " functions in section.";
136 } else {
137 // Parse the start of a single function.
138 int64_t BodySize, LocalEntryCount;
139 if (!nextLEB(BodySize, Bytes, Size, false) ||
140 !nextLEB(LocalEntryCount, Bytes, Size, false))
141 return std::nullopt;
142 if (LocalEntryCount) {
143 outs() << " .local ";
144 for (int64_t I = 0; I < LocalEntryCount; I++) {
145 int64_t Count, Type;
146 if (!nextLEB(Count, Bytes, Size, false) ||
147 !nextLEB(Type, Bytes, Size, false))
148 return std::nullopt;
149 for (int64_t J = 0; J < Count; J++) {
150 if (I || J)
151 outs() << ", ";
152 outs() << WebAssembly::anyTypeToString(Type);
153 }
154 }
155 }
156 }
157 outs() << "\n";
158 return MCDisassembler::Success;
159 }
160
getInstruction(MCInst & MI,uint64_t & Size,ArrayRef<uint8_t> Bytes,uint64_t,raw_ostream & CS) const161 MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction(
162 MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t /*Address*/,
163 raw_ostream &CS) const {
164 CommentStream = &CS;
165 Size = 0;
166 int Opc = nextByte(Bytes, Size);
167 if (Opc < 0)
168 return MCDisassembler::Fail;
169 const auto *WasmInst = &InstructionTable0[Opc];
170 // If this is a prefix byte, indirect to another table.
171 if (WasmInst->ET == ET_Prefix) {
172 WasmInst = nullptr;
173 // Linear search, so far only 2 entries.
174 for (auto PT = PrefixTable; PT->Table; PT++) {
175 if (PT->Prefix == Opc) {
176 WasmInst = PT->Table;
177 break;
178 }
179 }
180 if (!WasmInst)
181 return MCDisassembler::Fail;
182 int64_t PrefixedOpc;
183 if (!nextLEB(PrefixedOpc, Bytes, Size, false))
184 return MCDisassembler::Fail;
185 if (PrefixedOpc < 0 || PrefixedOpc >= WebAssemblyInstructionTableSize)
186 return MCDisassembler::Fail;
187 WasmInst += PrefixedOpc;
188 }
189 if (WasmInst->ET == ET_Unused)
190 return MCDisassembler::Fail;
191 // At this point we must have a valid instruction to decode.
192 assert(WasmInst->ET == ET_Instruction);
193 MI.setOpcode(WasmInst->Opcode);
194 // Parse any operands.
195 for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) {
196 auto OT = OperandTable[WasmInst->OperandStart + OPI];
197 switch (OT) {
198 // ULEB operands:
199 case WebAssembly::OPERAND_BASIC_BLOCK:
200 case WebAssembly::OPERAND_LOCAL:
201 case WebAssembly::OPERAND_GLOBAL:
202 case WebAssembly::OPERAND_FUNCTION32:
203 case WebAssembly::OPERAND_TABLE:
204 case WebAssembly::OPERAND_OFFSET32:
205 case WebAssembly::OPERAND_OFFSET64:
206 case WebAssembly::OPERAND_P2ALIGN:
207 case WebAssembly::OPERAND_TYPEINDEX:
208 case WebAssembly::OPERAND_TAG:
209 case MCOI::OPERAND_IMMEDIATE: {
210 if (!parseLEBImmediate(MI, Size, Bytes, false))
211 return MCDisassembler::Fail;
212 break;
213 }
214 // SLEB operands:
215 case WebAssembly::OPERAND_I32IMM:
216 case WebAssembly::OPERAND_I64IMM: {
217 if (!parseLEBImmediate(MI, Size, Bytes, true))
218 return MCDisassembler::Fail;
219 break;
220 }
221 // block_type operands:
222 case WebAssembly::OPERAND_SIGNATURE: {
223 int64_t Val;
224 uint64_t PrevSize = Size;
225 if (!nextLEB(Val, Bytes, Size, true))
226 return MCDisassembler::Fail;
227 if (Val < 0) {
228 // Negative values are single septet value types or empty types
229 if (Size != PrevSize + 1) {
230 MI.addOperand(
231 MCOperand::createImm(int64_t(WebAssembly::BlockType::Invalid)));
232 } else {
233 MI.addOperand(MCOperand::createImm(Val & 0x7f));
234 }
235 } else {
236 // We don't have access to the signature, so create a symbol without one
237 MCSymbol *Sym = getContext().createTempSymbol("typeindex", true);
238 auto *WasmSym = cast<MCSymbolWasm>(Sym);
239 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
240 const MCExpr *Expr = MCSymbolRefExpr::create(
241 WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, getContext());
242 MI.addOperand(MCOperand::createExpr(Expr));
243 }
244 break;
245 }
246 // FP operands.
247 case WebAssembly::OPERAND_F32IMM: {
248 if (!parseImmediate<float>(MI, Size, Bytes))
249 return MCDisassembler::Fail;
250 break;
251 }
252 case WebAssembly::OPERAND_F64IMM: {
253 if (!parseImmediate<double>(MI, Size, Bytes))
254 return MCDisassembler::Fail;
255 break;
256 }
257 // Vector lane operands (not LEB encoded).
258 case WebAssembly::OPERAND_VEC_I8IMM: {
259 if (!parseImmediate<uint8_t>(MI, Size, Bytes))
260 return MCDisassembler::Fail;
261 break;
262 }
263 case WebAssembly::OPERAND_VEC_I16IMM: {
264 if (!parseImmediate<uint16_t>(MI, Size, Bytes))
265 return MCDisassembler::Fail;
266 break;
267 }
268 case WebAssembly::OPERAND_VEC_I32IMM: {
269 if (!parseImmediate<uint32_t>(MI, Size, Bytes))
270 return MCDisassembler::Fail;
271 break;
272 }
273 case WebAssembly::OPERAND_VEC_I64IMM: {
274 if (!parseImmediate<uint64_t>(MI, Size, Bytes))
275 return MCDisassembler::Fail;
276 break;
277 }
278 case WebAssembly::OPERAND_BRLIST: {
279 int64_t TargetTableLen;
280 if (!nextLEB(TargetTableLen, Bytes, Size, false))
281 return MCDisassembler::Fail;
282 for (int64_t I = 0; I < TargetTableLen; I++) {
283 if (!parseLEBImmediate(MI, Size, Bytes, false))
284 return MCDisassembler::Fail;
285 }
286 // Default case.
287 if (!parseLEBImmediate(MI, Size, Bytes, false))
288 return MCDisassembler::Fail;
289 break;
290 }
291 case MCOI::OPERAND_REGISTER:
292 // The tablegen header currently does not have any register operands since
293 // we use only the stack (_S) instructions.
294 // If you hit this that probably means a bad instruction definition in
295 // tablegen.
296 llvm_unreachable("Register operand in WebAssemblyDisassembler");
297 default:
298 llvm_unreachable("Unknown operand type in WebAssemblyDisassembler");
299 }
300 }
301 return MCDisassembler::Success;
302 }
303