1 //===-- WebAssemblyAsmPrinter.cpp - WebAssembly LLVM assembly writer ------===//
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 contains a printer that converts from our internal
11 /// representation of machine-dependent LLVM code to the WebAssembly assembly
12 /// language.
13 ///
14 //===----------------------------------------------------------------------===//
15
16 #include "WebAssemblyAsmPrinter.h"
17 #include "MCTargetDesc/WebAssemblyInstPrinter.h"
18 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
19 #include "MCTargetDesc/WebAssemblyTargetStreamer.h"
20 #include "TargetInfo/WebAssemblyTargetInfo.h"
21 #include "WebAssembly.h"
22 #include "WebAssemblyMCInstLower.h"
23 #include "WebAssemblyMachineFunctionInfo.h"
24 #include "WebAssemblyRegisterInfo.h"
25 #include "WebAssemblyTargetMachine.h"
26 #include "llvm/ADT/SmallSet.h"
27 #include "llvm/ADT/StringExtras.h"
28 #include "llvm/BinaryFormat/Wasm.h"
29 #include "llvm/CodeGen/Analysis.h"
30 #include "llvm/CodeGen/AsmPrinter.h"
31 #include "llvm/CodeGen/MachineConstantPool.h"
32 #include "llvm/CodeGen/MachineInstr.h"
33 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
34 #include "llvm/IR/DataLayout.h"
35 #include "llvm/IR/DebugInfoMetadata.h"
36 #include "llvm/IR/GlobalVariable.h"
37 #include "llvm/IR/Metadata.h"
38 #include "llvm/MC/MCContext.h"
39 #include "llvm/MC/MCSectionWasm.h"
40 #include "llvm/MC/MCStreamer.h"
41 #include "llvm/MC/MCSymbol.h"
42 #include "llvm/MC/MCSymbolWasm.h"
43 #include "llvm/Support/Debug.h"
44 #include "llvm/Support/TargetRegistry.h"
45 #include "llvm/Support/raw_ostream.h"
46
47 using namespace llvm;
48
49 #define DEBUG_TYPE "asm-printer"
50
51 extern cl::opt<bool> WasmKeepRegisters;
52 extern cl::opt<bool> EnableEmException;
53 extern cl::opt<bool> EnableEmSjLj;
54
55 //===----------------------------------------------------------------------===//
56 // Helpers.
57 //===----------------------------------------------------------------------===//
58
getRegType(unsigned RegNo) const59 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
60 const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
61 const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
62 for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
63 MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
64 if (TRI->isTypeLegalForClass(*TRC, T))
65 return T;
66 LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
67 llvm_unreachable("Unknown register type");
68 return MVT::Other;
69 }
70
regToString(const MachineOperand & MO)71 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
72 Register RegNo = MO.getReg();
73 assert(Register::isVirtualRegister(RegNo) &&
74 "Unlowered physical register encountered during assembly printing");
75 assert(!MFI->isVRegStackified(RegNo));
76 unsigned WAReg = MFI->getWAReg(RegNo);
77 assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
78 return '$' + utostr(WAReg);
79 }
80
getTargetStreamer()81 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
82 MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
83 return static_cast<WebAssemblyTargetStreamer *>(TS);
84 }
85
86 // Emscripten exception handling helpers
87 //
88 // This converts invoke names generated by LowerEmscriptenEHSjLj to real names
89 // that are expected by JavaScript glue code. The invoke names generated by
90 // Emscripten JS glue code are based on their argument and return types; for
91 // example, for a function that takes an i32 and returns nothing, it is
92 // 'invoke_vi'. But the format of invoke generated by LowerEmscriptenEHSjLj pass
93 // contains a mangled string generated from their IR types, for example,
94 // "__invoke_void_%struct.mystruct*_int", because final wasm types are not
95 // available in the IR pass. So we convert those names to the form that
96 // Emscripten JS code expects.
97 //
98 // Refer to LowerEmscriptenEHSjLj pass for more details.
99
100 // Returns true if the given function name is an invoke name generated by
101 // LowerEmscriptenEHSjLj pass.
isEmscriptenInvokeName(StringRef Name)102 static bool isEmscriptenInvokeName(StringRef Name) {
103 if (Name.front() == '"' && Name.back() == '"')
104 Name = Name.substr(1, Name.size() - 2);
105 return Name.startswith("__invoke_");
106 }
107
108 // Returns a character that represents the given wasm value type in invoke
109 // signatures.
getInvokeSig(wasm::ValType VT)110 static char getInvokeSig(wasm::ValType VT) {
111 switch (VT) {
112 case wasm::ValType::I32:
113 return 'i';
114 case wasm::ValType::I64:
115 return 'j';
116 case wasm::ValType::F32:
117 return 'f';
118 case wasm::ValType::F64:
119 return 'd';
120 case wasm::ValType::V128:
121 return 'V';
122 case wasm::ValType::FUNCREF:
123 return 'F';
124 case wasm::ValType::EXTERNREF:
125 return 'X';
126 }
127 llvm_unreachable("Unhandled wasm::ValType enum");
128 }
129
130 // Given the wasm signature, generate the invoke name in the format JS glue code
131 // expects.
getEmscriptenInvokeSymbolName(wasm::WasmSignature * Sig)132 static std::string getEmscriptenInvokeSymbolName(wasm::WasmSignature *Sig) {
133 assert(Sig->Returns.size() <= 1);
134 std::string Ret = "invoke_";
135 if (!Sig->Returns.empty())
136 for (auto VT : Sig->Returns)
137 Ret += getInvokeSig(VT);
138 else
139 Ret += 'v';
140 // Invokes' first argument is a pointer to the original function, so skip it
141 for (unsigned I = 1, E = Sig->Params.size(); I < E; I++)
142 Ret += getInvokeSig(Sig->Params[I]);
143 return Ret;
144 }
145
146 //===----------------------------------------------------------------------===//
147 // WebAssemblyAsmPrinter Implementation.
148 //===----------------------------------------------------------------------===//
149
getMCSymbolForFunction(const Function * F,bool EnableEmEH,wasm::WasmSignature * Sig,bool & InvokeDetected)150 MCSymbolWasm *WebAssemblyAsmPrinter::getMCSymbolForFunction(
151 const Function *F, bool EnableEmEH, wasm::WasmSignature *Sig,
152 bool &InvokeDetected) {
153 MCSymbolWasm *WasmSym = nullptr;
154 if (EnableEmEH && isEmscriptenInvokeName(F->getName())) {
155 assert(Sig);
156 InvokeDetected = true;
157 if (Sig->Returns.size() > 1) {
158 std::string Msg =
159 "Emscripten EH/SjLj does not support multivalue returns: " +
160 std::string(F->getName()) + ": " +
161 WebAssembly::signatureToString(Sig);
162 report_fatal_error(Msg);
163 }
164 WasmSym = cast<MCSymbolWasm>(
165 GetExternalSymbolSymbol(getEmscriptenInvokeSymbolName(Sig)));
166 } else {
167 WasmSym = cast<MCSymbolWasm>(getSymbol(F));
168 }
169 return WasmSym;
170 }
171
emitEndOfAsmFile(Module & M)172 void WebAssemblyAsmPrinter::emitEndOfAsmFile(Module &M) {
173 for (auto &It : OutContext.getSymbols()) {
174 // Emit a .globaltype and .eventtype declaration.
175 auto Sym = cast<MCSymbolWasm>(It.getValue());
176 if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL)
177 getTargetStreamer()->emitGlobalType(Sym);
178 else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
179 getTargetStreamer()->emitEventType(Sym);
180 }
181
182 DenseSet<MCSymbol *> InvokeSymbols;
183 for (const auto &F : M) {
184 if (F.isIntrinsic())
185 continue;
186
187 // Emit function type info for all undefined functions
188 if (F.isDeclarationForLinker()) {
189 SmallVector<MVT, 4> Results;
190 SmallVector<MVT, 4> Params;
191 computeSignatureVTs(F.getFunctionType(), &F, F, TM, Params, Results);
192 // At this point these MCSymbols may or may not have been created already
193 // and thus also contain a signature, but we need to get the signature
194 // anyway here in case it is an invoke that has not yet been created. We
195 // will discard it later if it turns out not to be necessary.
196 auto Signature = signatureFromMVTs(Results, Params);
197 bool InvokeDetected = false;
198 auto *Sym = getMCSymbolForFunction(&F, EnableEmException || EnableEmSjLj,
199 Signature.get(), InvokeDetected);
200
201 // Multiple functions can be mapped to the same invoke symbol. For
202 // example, two IR functions '__invoke_void_i8*' and '__invoke_void_i32'
203 // are both mapped to '__invoke_vi'. We keep them in a set once we emit an
204 // Emscripten EH symbol so we don't emit the same symbol twice.
205 if (InvokeDetected && !InvokeSymbols.insert(Sym).second)
206 continue;
207
208 Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
209 if (!Sym->getSignature()) {
210 Sym->setSignature(Signature.get());
211 addSignature(std::move(Signature));
212 } else {
213 // This symbol has already been created and had a signature. Discard it.
214 Signature.reset();
215 }
216
217 getTargetStreamer()->emitFunctionType(Sym);
218
219 if (F.hasFnAttribute("wasm-import-module")) {
220 StringRef Name =
221 F.getFnAttribute("wasm-import-module").getValueAsString();
222 Sym->setImportModule(storeName(Name));
223 getTargetStreamer()->emitImportModule(Sym, Name);
224 }
225 if (F.hasFnAttribute("wasm-import-name")) {
226 // If this is a converted Emscripten EH/SjLj symbol, we shouldn't use
227 // the original function name but the converted symbol name.
228 StringRef Name =
229 InvokeDetected
230 ? Sym->getName()
231 : F.getFnAttribute("wasm-import-name").getValueAsString();
232 Sym->setImportName(storeName(Name));
233 getTargetStreamer()->emitImportName(Sym, Name);
234 }
235 }
236
237 if (F.hasFnAttribute("wasm-export-name")) {
238 auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
239 StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
240 Sym->setExportName(storeName(Name));
241 getTargetStreamer()->emitExportName(Sym, Name);
242 }
243 }
244
245 for (const auto &G : M.globals()) {
246 if (!G.hasInitializer() && G.hasExternalLinkage()) {
247 if (G.getValueType()->isSized()) {
248 uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
249 OutStreamer->emitELFSize(getSymbol(&G),
250 MCConstantExpr::create(Size, OutContext));
251 }
252 }
253 }
254
255 if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
256 for (const Metadata *MD : Named->operands()) {
257 const auto *Tuple = dyn_cast<MDTuple>(MD);
258 if (!Tuple || Tuple->getNumOperands() != 2)
259 continue;
260 const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
261 const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
262 if (!Name || !Contents)
263 continue;
264
265 OutStreamer->PushSection();
266 std::string SectionName = (".custom_section." + Name->getString()).str();
267 MCSectionWasm *MySection =
268 OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
269 OutStreamer->SwitchSection(MySection);
270 OutStreamer->emitBytes(Contents->getString());
271 OutStreamer->PopSection();
272 }
273 }
274
275 EmitProducerInfo(M);
276 EmitTargetFeatures(M);
277 }
278
EmitProducerInfo(Module & M)279 void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
280 llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
281 if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
282 llvm::SmallSet<StringRef, 4> SeenLanguages;
283 for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
284 const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
285 StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
286 Language.consume_front("DW_LANG_");
287 if (SeenLanguages.insert(Language).second)
288 Languages.emplace_back(Language.str(), "");
289 }
290 }
291
292 llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
293 if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
294 llvm::SmallSet<StringRef, 4> SeenTools;
295 for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
296 const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
297 std::pair<StringRef, StringRef> Field = S->getString().split("version");
298 StringRef Name = Field.first.trim();
299 StringRef Version = Field.second.trim();
300 if (SeenTools.insert(Name).second)
301 Tools.emplace_back(Name.str(), Version.str());
302 }
303 }
304
305 int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
306 if (FieldCount != 0) {
307 MCSectionWasm *Producers = OutContext.getWasmSection(
308 ".custom_section.producers", SectionKind::getMetadata());
309 OutStreamer->PushSection();
310 OutStreamer->SwitchSection(Producers);
311 OutStreamer->emitULEB128IntValue(FieldCount);
312 for (auto &Producers : {std::make_pair("language", &Languages),
313 std::make_pair("processed-by", &Tools)}) {
314 if (Producers.second->empty())
315 continue;
316 OutStreamer->emitULEB128IntValue(strlen(Producers.first));
317 OutStreamer->emitBytes(Producers.first);
318 OutStreamer->emitULEB128IntValue(Producers.second->size());
319 for (auto &Producer : *Producers.second) {
320 OutStreamer->emitULEB128IntValue(Producer.first.size());
321 OutStreamer->emitBytes(Producer.first);
322 OutStreamer->emitULEB128IntValue(Producer.second.size());
323 OutStreamer->emitBytes(Producer.second);
324 }
325 }
326 OutStreamer->PopSection();
327 }
328 }
329
EmitTargetFeatures(Module & M)330 void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
331 struct FeatureEntry {
332 uint8_t Prefix;
333 std::string Name;
334 };
335
336 // Read target features and linkage policies from module metadata
337 SmallVector<FeatureEntry, 4> EmittedFeatures;
338 auto EmitFeature = [&](std::string Feature) {
339 std::string MDKey = (StringRef("wasm-feature-") + Feature).str();
340 Metadata *Policy = M.getModuleFlag(MDKey);
341 if (Policy == nullptr)
342 return;
343
344 FeatureEntry Entry;
345 Entry.Prefix = 0;
346 Entry.Name = Feature;
347
348 if (auto *MD = cast<ConstantAsMetadata>(Policy))
349 if (auto *I = cast<ConstantInt>(MD->getValue()))
350 Entry.Prefix = I->getZExtValue();
351
352 // Silently ignore invalid metadata
353 if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
354 Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
355 Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
356 return;
357
358 EmittedFeatures.push_back(Entry);
359 };
360
361 for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
362 EmitFeature(KV.Key);
363 }
364 // This pseudo-feature tells the linker whether shared memory would be safe
365 EmitFeature("shared-mem");
366
367 if (EmittedFeatures.size() == 0)
368 return;
369
370 // Emit features and linkage policies into the "target_features" section
371 MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
372 ".custom_section.target_features", SectionKind::getMetadata());
373 OutStreamer->PushSection();
374 OutStreamer->SwitchSection(FeaturesSection);
375
376 OutStreamer->emitULEB128IntValue(EmittedFeatures.size());
377 for (auto &F : EmittedFeatures) {
378 OutStreamer->emitIntValue(F.Prefix, 1);
379 OutStreamer->emitULEB128IntValue(F.Name.size());
380 OutStreamer->emitBytes(F.Name);
381 }
382
383 OutStreamer->PopSection();
384 }
385
emitConstantPool()386 void WebAssemblyAsmPrinter::emitConstantPool() {
387 assert(MF->getConstantPool()->getConstants().empty() &&
388 "WebAssembly disables constant pools");
389 }
390
emitJumpTableInfo()391 void WebAssemblyAsmPrinter::emitJumpTableInfo() {
392 // Nothing to do; jump tables are incorporated into the instruction stream.
393 }
394
emitFunctionBodyStart()395 void WebAssemblyAsmPrinter::emitFunctionBodyStart() {
396 const Function &F = MF->getFunction();
397 SmallVector<MVT, 1> ResultVTs;
398 SmallVector<MVT, 4> ParamVTs;
399 computeSignatureVTs(F.getFunctionType(), &F, F, TM, ParamVTs, ResultVTs);
400
401 auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
402 auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
403 WasmSym->setSignature(Signature.get());
404 addSignature(std::move(Signature));
405 WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
406
407 getTargetStreamer()->emitFunctionType(WasmSym);
408
409 // Emit the function index.
410 if (MDNode *Idx = F.getMetadata("wasm.index")) {
411 assert(Idx->getNumOperands() == 1);
412
413 getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
414 cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
415 }
416
417 SmallVector<wasm::ValType, 16> Locals;
418 valTypesFromMVTs(MFI->getLocals(), Locals);
419 getTargetStreamer()->emitLocal(Locals);
420
421 AsmPrinter::emitFunctionBodyStart();
422 }
423
emitInstruction(const MachineInstr * MI)424 void WebAssemblyAsmPrinter::emitInstruction(const MachineInstr *MI) {
425 LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
426
427 switch (MI->getOpcode()) {
428 case WebAssembly::ARGUMENT_i32:
429 case WebAssembly::ARGUMENT_i32_S:
430 case WebAssembly::ARGUMENT_i64:
431 case WebAssembly::ARGUMENT_i64_S:
432 case WebAssembly::ARGUMENT_f32:
433 case WebAssembly::ARGUMENT_f32_S:
434 case WebAssembly::ARGUMENT_f64:
435 case WebAssembly::ARGUMENT_f64_S:
436 case WebAssembly::ARGUMENT_v16i8:
437 case WebAssembly::ARGUMENT_v16i8_S:
438 case WebAssembly::ARGUMENT_v8i16:
439 case WebAssembly::ARGUMENT_v8i16_S:
440 case WebAssembly::ARGUMENT_v4i32:
441 case WebAssembly::ARGUMENT_v4i32_S:
442 case WebAssembly::ARGUMENT_v2i64:
443 case WebAssembly::ARGUMENT_v2i64_S:
444 case WebAssembly::ARGUMENT_v4f32:
445 case WebAssembly::ARGUMENT_v4f32_S:
446 case WebAssembly::ARGUMENT_v2f64:
447 case WebAssembly::ARGUMENT_v2f64_S:
448 // These represent values which are live into the function entry, so there's
449 // no instruction to emit.
450 break;
451 case WebAssembly::FALLTHROUGH_RETURN: {
452 // These instructions represent the implicit return at the end of a
453 // function body.
454 if (isVerbose()) {
455 OutStreamer->AddComment("fallthrough-return");
456 OutStreamer->AddBlankLine();
457 }
458 break;
459 }
460 case WebAssembly::COMPILER_FENCE:
461 // This is a compiler barrier that prevents instruction reordering during
462 // backend compilation, and should not be emitted.
463 break;
464 default: {
465 WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
466 MCInst TmpInst;
467 MCInstLowering.lower(MI, TmpInst);
468 EmitToStreamer(*OutStreamer, TmpInst);
469 break;
470 }
471 }
472 }
473
PrintAsmOperand(const MachineInstr * MI,unsigned OpNo,const char * ExtraCode,raw_ostream & OS)474 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
475 unsigned OpNo,
476 const char *ExtraCode,
477 raw_ostream &OS) {
478 // First try the generic code, which knows about modifiers like 'c' and 'n'.
479 if (!AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, OS))
480 return false;
481
482 if (!ExtraCode) {
483 const MachineOperand &MO = MI->getOperand(OpNo);
484 switch (MO.getType()) {
485 case MachineOperand::MO_Immediate:
486 OS << MO.getImm();
487 return false;
488 case MachineOperand::MO_Register:
489 // FIXME: only opcode that still contains registers, as required by
490 // MachineInstr::getDebugVariable().
491 assert(MI->getOpcode() == WebAssembly::INLINEASM);
492 OS << regToString(MO);
493 return false;
494 case MachineOperand::MO_GlobalAddress:
495 PrintSymbolOperand(MO, OS);
496 return false;
497 case MachineOperand::MO_ExternalSymbol:
498 GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
499 printOffset(MO.getOffset(), OS);
500 return false;
501 case MachineOperand::MO_MachineBasicBlock:
502 MO.getMBB()->getSymbol()->print(OS, MAI);
503 return false;
504 default:
505 break;
506 }
507 }
508
509 return true;
510 }
511
PrintAsmMemoryOperand(const MachineInstr * MI,unsigned OpNo,const char * ExtraCode,raw_ostream & OS)512 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
513 unsigned OpNo,
514 const char *ExtraCode,
515 raw_ostream &OS) {
516 // The current approach to inline asm is that "r" constraints are expressed
517 // as local indices, rather than values on the operand stack. This simplifies
518 // using "r" as it eliminates the need to push and pop the values in a
519 // particular order, however it also makes it impossible to have an "m"
520 // constraint. So we don't support it.
521
522 return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, ExtraCode, OS);
523 }
524
525 // Force static initialization.
LLVMInitializeWebAssemblyAsmPrinter()526 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyAsmPrinter() {
527 RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
528 RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
529 }
530