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/WebAssemblyInstPrinter.h"
18 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
19 #include "TargetInfo/WebAssemblyTargetInfo.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCDisassembler/MCDisassembler.h"
22 #include "llvm/MC/MCFixedLenDisassembler.h"
23 #include "llvm/MC/MCInst.h"
24 #include "llvm/MC/MCInstrInfo.h"
25 #include "llvm/MC/MCSubtargetInfo.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/MC/MCSymbolWasm.h"
28 #include "llvm/Support/Endian.h"
29 #include "llvm/Support/LEB128.h"
30 #include "llvm/Support/TargetRegistry.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   DecodeStatus onSymbolStart(StringRef Name, uint64_t &Size,
50                              ArrayRef<uint8_t> Bytes, uint64_t Address,
51                              raw_ostream &CStream) const override;
52 
53 public:
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 
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
68 LLVMInitializeWebAssemblyDisassembler() {
69   // Register the disassembler for each target.
70   TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(),
71                                          createWebAssemblyDisassembler);
72   TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget64(),
73                                          createWebAssemblyDisassembler);
74 }
75 
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 
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 
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>
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 = support::endian::read<T, support::endianness::little, 1>(
113       Bytes.data() + Size);
114   Size += sizeof(T);
115   if (std::is_floating_point<T>::value) {
116     MI.addOperand(MCOperand::createFPImm(static_cast<double>(Val)));
117   } else {
118     MI.addOperand(MCOperand::createImm(static_cast<int64_t>(Val)));
119   }
120   return true;
121 }
122 
123 MCDisassembler::DecodeStatus WebAssemblyDisassembler::onSymbolStart(
124     StringRef Name, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t Address,
125     raw_ostream &CStream) const {
126   Size = 0;
127   if (Address == 0) {
128     // Start of a code section: we're parsing only the function count.
129     int64_t FunctionCount;
130     if (!nextLEB(FunctionCount, Bytes, Size, false))
131       return MCDisassembler::Fail;
132     outs() << "        # " << FunctionCount << " functions in section.";
133   } else {
134     // Parse the start of a single function.
135     int64_t BodySize, LocalEntryCount;
136     if (!nextLEB(BodySize, Bytes, Size, false) ||
137         !nextLEB(LocalEntryCount, Bytes, Size, false))
138       return MCDisassembler::Fail;
139     if (LocalEntryCount) {
140       outs() << "        .local ";
141       for (int64_t I = 0; I < LocalEntryCount; I++) {
142         int64_t Count, Type;
143         if (!nextLEB(Count, Bytes, Size, false) ||
144             !nextLEB(Type, Bytes, Size, false))
145           return MCDisassembler::Fail;
146         for (int64_t J = 0; J < Count; J++) {
147           if (I || J)
148             outs() << ", ";
149           outs() << WebAssembly::anyTypeToString(Type);
150         }
151       }
152     }
153   }
154   outs() << "\n";
155   return MCDisassembler::Success;
156 }
157 
158 MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction(
159     MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t /*Address*/,
160     raw_ostream &CS) const {
161   CommentStream = &CS;
162   Size = 0;
163   int Opc = nextByte(Bytes, Size);
164   if (Opc < 0)
165     return MCDisassembler::Fail;
166   const auto *WasmInst = &InstructionTable0[Opc];
167   // If this is a prefix byte, indirect to another table.
168   if (WasmInst->ET == ET_Prefix) {
169     WasmInst = nullptr;
170     // Linear search, so far only 2 entries.
171     for (auto PT = PrefixTable; PT->Table; PT++) {
172       if (PT->Prefix == Opc) {
173         WasmInst = PT->Table;
174         break;
175       }
176     }
177     if (!WasmInst)
178       return MCDisassembler::Fail;
179     int64_t PrefixedOpc;
180     if (!nextLEB(PrefixedOpc, Bytes, Size, false))
181       return MCDisassembler::Fail;
182     if (PrefixedOpc < 0 || PrefixedOpc >= WebAssemblyInstructionTableSize)
183       return MCDisassembler::Fail;
184     WasmInst += PrefixedOpc;
185   }
186   if (WasmInst->ET == ET_Unused)
187     return MCDisassembler::Fail;
188   // At this point we must have a valid instruction to decode.
189   assert(WasmInst->ET == ET_Instruction);
190   MI.setOpcode(WasmInst->Opcode);
191   // Parse any operands.
192   for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) {
193     auto OT = OperandTable[WasmInst->OperandStart + OPI];
194     switch (OT) {
195     // ULEB operands:
196     case WebAssembly::OPERAND_BASIC_BLOCK:
197     case WebAssembly::OPERAND_LOCAL:
198     case WebAssembly::OPERAND_GLOBAL:
199     case WebAssembly::OPERAND_FUNCTION32:
200     case WebAssembly::OPERAND_OFFSET32:
201     case WebAssembly::OPERAND_P2ALIGN:
202     case WebAssembly::OPERAND_TYPEINDEX:
203     case WebAssembly::OPERAND_EVENT:
204     case MCOI::OPERAND_IMMEDIATE: {
205       if (!parseLEBImmediate(MI, Size, Bytes, false))
206         return MCDisassembler::Fail;
207       break;
208     }
209     // SLEB operands:
210     case WebAssembly::OPERAND_I32IMM:
211     case WebAssembly::OPERAND_I64IMM: {
212       if (!parseLEBImmediate(MI, Size, Bytes, true))
213         return MCDisassembler::Fail;
214       break;
215     }
216     // block_type operands:
217     case WebAssembly::OPERAND_SIGNATURE: {
218       int64_t Val;
219       uint64_t PrevSize = Size;
220       if (!nextLEB(Val, Bytes, Size, true))
221         return MCDisassembler::Fail;
222       if (Val < 0) {
223         // Negative values are single septet value types or empty types
224         if (Size != PrevSize + 1) {
225           MI.addOperand(
226               MCOperand::createImm(int64_t(WebAssembly::BlockType::Invalid)));
227         } else {
228           MI.addOperand(MCOperand::createImm(Val & 0x7f));
229         }
230       } else {
231         // We don't have access to the signature, so create a symbol without one
232         MCSymbol *Sym = getContext().createTempSymbol("typeindex", true);
233         auto *WasmSym = cast<MCSymbolWasm>(Sym);
234         WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
235         const MCExpr *Expr = MCSymbolRefExpr::create(
236             WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, getContext());
237         MI.addOperand(MCOperand::createExpr(Expr));
238       }
239       break;
240     }
241     // FP operands.
242     case WebAssembly::OPERAND_F32IMM: {
243       if (!parseImmediate<float>(MI, Size, Bytes))
244         return MCDisassembler::Fail;
245       break;
246     }
247     case WebAssembly::OPERAND_F64IMM: {
248       if (!parseImmediate<double>(MI, Size, Bytes))
249         return MCDisassembler::Fail;
250       break;
251     }
252     // Vector lane operands (not LEB encoded).
253     case WebAssembly::OPERAND_VEC_I8IMM: {
254       if (!parseImmediate<uint8_t>(MI, Size, Bytes))
255         return MCDisassembler::Fail;
256       break;
257     }
258     case WebAssembly::OPERAND_VEC_I16IMM: {
259       if (!parseImmediate<uint16_t>(MI, Size, Bytes))
260         return MCDisassembler::Fail;
261       break;
262     }
263     case WebAssembly::OPERAND_VEC_I32IMM: {
264       if (!parseImmediate<uint32_t>(MI, Size, Bytes))
265         return MCDisassembler::Fail;
266       break;
267     }
268     case WebAssembly::OPERAND_VEC_I64IMM: {
269       if (!parseImmediate<uint64_t>(MI, Size, Bytes))
270         return MCDisassembler::Fail;
271       break;
272     }
273     case WebAssembly::OPERAND_BRLIST: {
274       int64_t TargetTableLen;
275       if (!nextLEB(TargetTableLen, Bytes, Size, false))
276         return MCDisassembler::Fail;
277       for (int64_t I = 0; I < TargetTableLen; I++) {
278         if (!parseLEBImmediate(MI, Size, Bytes, false))
279           return MCDisassembler::Fail;
280       }
281       // Default case.
282       if (!parseLEBImmediate(MI, Size, Bytes, false))
283         return MCDisassembler::Fail;
284       break;
285     }
286     case MCOI::OPERAND_REGISTER:
287       // The tablegen header currently does not have any register operands since
288       // we use only the stack (_S) instructions.
289       // If you hit this that probably means a bad instruction definition in
290       // tablegen.
291       llvm_unreachable("Register operand in WebAssemblyDisassembler");
292     default:
293       llvm_unreachable("Unknown operand type in WebAssemblyDisassembler");
294     }
295   }
296   return MCDisassembler::Success;
297 }
298