1 //=- WebAssemblyMCCodeEmitter.cpp - Convert WebAssembly 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 /// \file
10 /// This file implements the WebAssemblyMCCodeEmitter class.
11 ///
12 //===----------------------------------------------------------------------===//
13 
14 #include "MCTargetDesc/WebAssemblyFixupKinds.h"
15 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/Statistic.h"
18 #include "llvm/MC/MCCodeEmitter.h"
19 #include "llvm/MC/MCFixup.h"
20 #include "llvm/MC/MCInst.h"
21 #include "llvm/MC/MCInstrInfo.h"
22 #include "llvm/MC/MCRegisterInfo.h"
23 #include "llvm/MC/MCSubtargetInfo.h"
24 #include "llvm/MC/MCSymbol.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/EndianStream.h"
27 #include "llvm/Support/LEB128.h"
28 #include "llvm/Support/raw_ostream.h"
29 
30 using namespace llvm;
31 
32 #define DEBUG_TYPE "mccodeemitter"
33 
34 STATISTIC(MCNumEmitted, "Number of MC instructions emitted.");
35 STATISTIC(MCNumFixups, "Number of MC fixups created.");
36 
37 namespace {
38 class WebAssemblyMCCodeEmitter final : public MCCodeEmitter {
39   const MCInstrInfo &MCII;
40 
41   // Implementation generated by tablegen.
42   uint64_t getBinaryCodeForInstr(const MCInst &MI,
43                                  SmallVectorImpl<MCFixup> &Fixups,
44                                  const MCSubtargetInfo &STI) const;
45 
46   void encodeInstruction(const MCInst &MI, raw_ostream &OS,
47                          SmallVectorImpl<MCFixup> &Fixups,
48                          const MCSubtargetInfo &STI) const override;
49 
50 public:
51   WebAssemblyMCCodeEmitter(const MCInstrInfo &MCII) : MCII(MCII) {}
52 };
53 } // end anonymous namespace
54 
55 MCCodeEmitter *llvm::createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII) {
56   return new WebAssemblyMCCodeEmitter(MCII);
57 }
58 
59 void WebAssemblyMCCodeEmitter::encodeInstruction(
60     const MCInst &MI, raw_ostream &OS, SmallVectorImpl<MCFixup> &Fixups,
61     const MCSubtargetInfo &STI) const {
62   uint64_t Start = OS.tell();
63 
64   uint64_t Binary = getBinaryCodeForInstr(MI, Fixups, STI);
65   if (Binary < (1 << 8)) {
66     OS << uint8_t(Binary);
67   } else if (Binary < (1 << 16)) {
68     OS << uint8_t(Binary >> 8);
69     encodeULEB128(uint8_t(Binary), OS);
70   } else if (Binary < (1 << 24)) {
71     OS << uint8_t(Binary >> 16);
72     encodeULEB128(uint16_t(Binary), OS);
73   } else {
74     llvm_unreachable("Very large (prefix + 3 byte) opcodes not supported");
75   }
76 
77   // For br_table instructions, encode the size of the table. In the MCInst,
78   // there's an index operand (if not a stack instruction), one operand for
79   // each table entry, and the default operand.
80   if (MI.getOpcode() == WebAssembly::BR_TABLE_I32_S ||
81       MI.getOpcode() == WebAssembly::BR_TABLE_I64_S)
82     encodeULEB128(MI.getNumOperands() - 1, OS);
83   if (MI.getOpcode() == WebAssembly::BR_TABLE_I32 ||
84       MI.getOpcode() == WebAssembly::BR_TABLE_I64)
85     encodeULEB128(MI.getNumOperands() - 2, OS);
86 
87   const MCInstrDesc &Desc = MCII.get(MI.getOpcode());
88   for (unsigned I = 0, E = MI.getNumOperands(); I < E; ++I) {
89     const MCOperand &MO = MI.getOperand(I);
90     if (MO.isReg()) {
91       /* nothing to encode */
92 
93     } else if (MO.isImm()) {
94       if (I < Desc.getNumOperands()) {
95         const MCOperandInfo &Info = Desc.OpInfo[I];
96         LLVM_DEBUG(dbgs() << "Encoding immediate: type="
97                           << int(Info.OperandType) << "\n");
98         switch (Info.OperandType) {
99         case WebAssembly::OPERAND_I32IMM:
100           encodeSLEB128(int32_t(MO.getImm()), OS);
101           break;
102         case WebAssembly::OPERAND_OFFSET32:
103           encodeULEB128(uint32_t(MO.getImm()), OS);
104           break;
105         case WebAssembly::OPERAND_I64IMM:
106           encodeSLEB128(int64_t(MO.getImm()), OS);
107           break;
108         case WebAssembly::OPERAND_SIGNATURE:
109           OS << uint8_t(MO.getImm());
110           break;
111         case WebAssembly::OPERAND_VEC_I8IMM:
112           support::endian::write<uint8_t>(OS, MO.getImm(), support::little);
113           break;
114         case WebAssembly::OPERAND_VEC_I16IMM:
115           support::endian::write<uint16_t>(OS, MO.getImm(), support::little);
116           break;
117         case WebAssembly::OPERAND_VEC_I32IMM:
118           support::endian::write<uint32_t>(OS, MO.getImm(), support::little);
119           break;
120         case WebAssembly::OPERAND_VEC_I64IMM:
121           support::endian::write<uint64_t>(OS, MO.getImm(), support::little);
122           break;
123         case WebAssembly::OPERAND_GLOBAL:
124           llvm_unreachable("wasm globals should only be accessed symbolicly");
125         default:
126           encodeULEB128(uint64_t(MO.getImm()), OS);
127         }
128       } else {
129         encodeULEB128(uint64_t(MO.getImm()), OS);
130       }
131 
132     } else if (MO.isFPImm()) {
133       const MCOperandInfo &Info = Desc.OpInfo[I];
134       if (Info.OperandType == WebAssembly::OPERAND_F32IMM) {
135         // TODO: MC converts all floating point immediate operands to double.
136         // This is fine for numeric values, but may cause NaNs to change bits.
137         auto F = float(MO.getFPImm());
138         support::endian::write<float>(OS, F, support::little);
139       } else {
140         assert(Info.OperandType == WebAssembly::OPERAND_F64IMM);
141         double D = MO.getFPImm();
142         support::endian::write<double>(OS, D, support::little);
143       }
144 
145     } else if (MO.isExpr()) {
146       const MCOperandInfo &Info = Desc.OpInfo[I];
147       llvm::MCFixupKind FixupKind;
148       size_t PaddedSize = 5;
149       switch (Info.OperandType) {
150       case WebAssembly::OPERAND_I32IMM:
151         FixupKind = MCFixupKind(WebAssembly::fixup_sleb128_i32);
152         break;
153       case WebAssembly::OPERAND_I64IMM:
154         FixupKind = MCFixupKind(WebAssembly::fixup_sleb128_i64);
155         PaddedSize = 10;
156         break;
157       case WebAssembly::OPERAND_FUNCTION32:
158       case WebAssembly::OPERAND_TABLE:
159       case WebAssembly::OPERAND_OFFSET32:
160       case WebAssembly::OPERAND_SIGNATURE:
161       case WebAssembly::OPERAND_TYPEINDEX:
162       case WebAssembly::OPERAND_GLOBAL:
163       case WebAssembly::OPERAND_EVENT:
164         FixupKind = MCFixupKind(WebAssembly::fixup_uleb128_i32);
165         break;
166       case WebAssembly::OPERAND_OFFSET64:
167         FixupKind = MCFixupKind(WebAssembly::fixup_uleb128_i64);
168         PaddedSize = 10;
169         break;
170       default:
171         llvm_unreachable("unexpected symbolic operand kind");
172       }
173       Fixups.push_back(MCFixup::create(OS.tell() - Start, MO.getExpr(),
174                                        FixupKind, MI.getLoc()));
175       ++MCNumFixups;
176       encodeULEB128(0, OS, PaddedSize);
177     } else {
178       llvm_unreachable("unexpected operand kind");
179     }
180   }
181 
182   ++MCNumEmitted; // Keep track of the # of mi's emitted.
183 }
184 
185 #include "WebAssemblyGenMCCodeEmitter.inc"
186