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 
53 //===----------------------------------------------------------------------===//
54 // Helpers.
55 //===----------------------------------------------------------------------===//
56 
getRegType(unsigned RegNo) const57 MVT WebAssemblyAsmPrinter::getRegType(unsigned RegNo) const {
58   const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
59   const TargetRegisterClass *TRC = MRI->getRegClass(RegNo);
60   for (MVT T : {MVT::i32, MVT::i64, MVT::f32, MVT::f64, MVT::v16i8, MVT::v8i16,
61                 MVT::v4i32, MVT::v2i64, MVT::v4f32, MVT::v2f64})
62     if (TRI->isTypeLegalForClass(*TRC, T))
63       return T;
64   LLVM_DEBUG(errs() << "Unknown type for register number: " << RegNo);
65   llvm_unreachable("Unknown register type");
66   return MVT::Other;
67 }
68 
regToString(const MachineOperand & MO)69 std::string WebAssemblyAsmPrinter::regToString(const MachineOperand &MO) {
70   Register RegNo = MO.getReg();
71   assert(Register::isVirtualRegister(RegNo) &&
72          "Unlowered physical register encountered during assembly printing");
73   assert(!MFI->isVRegStackified(RegNo));
74   unsigned WAReg = MFI->getWAReg(RegNo);
75   assert(WAReg != WebAssemblyFunctionInfo::UnusedReg);
76   return '$' + utostr(WAReg);
77 }
78 
getTargetStreamer()79 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
80   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
81   return static_cast<WebAssemblyTargetStreamer *>(TS);
82 }
83 
84 //===----------------------------------------------------------------------===//
85 // WebAssemblyAsmPrinter Implementation.
86 //===----------------------------------------------------------------------===//
87 
EmitEndOfAsmFile(Module & M)88 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
89   for (auto &It : OutContext.getSymbols()) {
90     // Emit a .globaltype and .eventtype declaration.
91     auto Sym = cast<MCSymbolWasm>(It.getValue());
92     if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL)
93       getTargetStreamer()->emitGlobalType(Sym);
94     else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
95       getTargetStreamer()->emitEventType(Sym);
96   }
97 
98   for (const auto &F : M) {
99     if (F.isIntrinsic())
100       continue;
101 
102     // Emit function type info for all undefined functions
103     if (F.isDeclarationForLinker()) {
104       SmallVector<MVT, 4> Results;
105       SmallVector<MVT, 4> Params;
106       computeSignatureVTs(F.getFunctionType(), F, TM, Params, Results);
107       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
108       Sym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
109       if (!Sym->getSignature()) {
110         auto Signature = signatureFromMVTs(Results, Params);
111         Sym->setSignature(Signature.get());
112         addSignature(std::move(Signature));
113       }
114       // FIXME: this was originally intended for post-linking and was only used
115       // for imports that were only called indirectly (i.e. s2wasm could not
116       // infer the type from a call). With object files it applies to all
117       // imports. so fix the names and the tests, or rethink how import
118       // delcarations work in asm files.
119       getTargetStreamer()->emitFunctionType(Sym);
120 
121       if (TM.getTargetTriple().isOSBinFormatWasm() &&
122           F.hasFnAttribute("wasm-import-module")) {
123         StringRef Name =
124             F.getFnAttribute("wasm-import-module").getValueAsString();
125         Sym->setImportModule(Name);
126         getTargetStreamer()->emitImportModule(Sym, Name);
127       }
128       if (TM.getTargetTriple().isOSBinFormatWasm() &&
129           F.hasFnAttribute("wasm-import-name")) {
130         StringRef Name =
131             F.getFnAttribute("wasm-import-name").getValueAsString();
132         Sym->setImportName(Name);
133         getTargetStreamer()->emitImportName(Sym, Name);
134       }
135     }
136 
137     if (F.hasFnAttribute("wasm-export-name")) {
138       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
139       StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
140       Sym->setExportName(Name);
141       getTargetStreamer()->emitExportName(Sym, Name);
142     }
143   }
144 
145   for (const auto &G : M.globals()) {
146     if (!G.hasInitializer() && G.hasExternalLinkage()) {
147       if (G.getValueType()->isSized()) {
148         uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
149         OutStreamer->emitELFSize(getSymbol(&G),
150                                  MCConstantExpr::create(Size, OutContext));
151       }
152     }
153   }
154 
155   if (const NamedMDNode *Named = M.getNamedMetadata("wasm.custom_sections")) {
156     for (const Metadata *MD : Named->operands()) {
157       const auto *Tuple = dyn_cast<MDTuple>(MD);
158       if (!Tuple || Tuple->getNumOperands() != 2)
159         continue;
160       const MDString *Name = dyn_cast<MDString>(Tuple->getOperand(0));
161       const MDString *Contents = dyn_cast<MDString>(Tuple->getOperand(1));
162       if (!Name || !Contents)
163         continue;
164 
165       OutStreamer->PushSection();
166       std::string SectionName = (".custom_section." + Name->getString()).str();
167       MCSectionWasm *MySection =
168           OutContext.getWasmSection(SectionName, SectionKind::getMetadata());
169       OutStreamer->SwitchSection(MySection);
170       OutStreamer->EmitBytes(Contents->getString());
171       OutStreamer->PopSection();
172     }
173   }
174 
175   EmitProducerInfo(M);
176   EmitTargetFeatures(M);
177 }
178 
EmitProducerInfo(Module & M)179 void WebAssemblyAsmPrinter::EmitProducerInfo(Module &M) {
180   llvm::SmallVector<std::pair<std::string, std::string>, 4> Languages;
181   if (const NamedMDNode *Debug = M.getNamedMetadata("llvm.dbg.cu")) {
182     llvm::SmallSet<StringRef, 4> SeenLanguages;
183     for (size_t I = 0, E = Debug->getNumOperands(); I < E; ++I) {
184       const auto *CU = cast<DICompileUnit>(Debug->getOperand(I));
185       StringRef Language = dwarf::LanguageString(CU->getSourceLanguage());
186       Language.consume_front("DW_LANG_");
187       if (SeenLanguages.insert(Language).second)
188         Languages.emplace_back(Language.str(), "");
189     }
190   }
191 
192   llvm::SmallVector<std::pair<std::string, std::string>, 4> Tools;
193   if (const NamedMDNode *Ident = M.getNamedMetadata("llvm.ident")) {
194     llvm::SmallSet<StringRef, 4> SeenTools;
195     for (size_t I = 0, E = Ident->getNumOperands(); I < E; ++I) {
196       const auto *S = cast<MDString>(Ident->getOperand(I)->getOperand(0));
197       std::pair<StringRef, StringRef> Field = S->getString().split("version");
198       StringRef Name = Field.first.trim();
199       StringRef Version = Field.second.trim();
200       if (SeenTools.insert(Name).second)
201         Tools.emplace_back(Name.str(), Version.str());
202     }
203   }
204 
205   int FieldCount = int(!Languages.empty()) + int(!Tools.empty());
206   if (FieldCount != 0) {
207     MCSectionWasm *Producers = OutContext.getWasmSection(
208         ".custom_section.producers", SectionKind::getMetadata());
209     OutStreamer->PushSection();
210     OutStreamer->SwitchSection(Producers);
211     OutStreamer->EmitULEB128IntValue(FieldCount);
212     for (auto &Producers : {std::make_pair("language", &Languages),
213             std::make_pair("processed-by", &Tools)}) {
214       if (Producers.second->empty())
215         continue;
216       OutStreamer->EmitULEB128IntValue(strlen(Producers.first));
217       OutStreamer->EmitBytes(Producers.first);
218       OutStreamer->EmitULEB128IntValue(Producers.second->size());
219       for (auto &Producer : *Producers.second) {
220         OutStreamer->EmitULEB128IntValue(Producer.first.size());
221         OutStreamer->EmitBytes(Producer.first);
222         OutStreamer->EmitULEB128IntValue(Producer.second.size());
223         OutStreamer->EmitBytes(Producer.second);
224       }
225     }
226     OutStreamer->PopSection();
227   }
228 }
229 
EmitTargetFeatures(Module & M)230 void WebAssemblyAsmPrinter::EmitTargetFeatures(Module &M) {
231   struct FeatureEntry {
232     uint8_t Prefix;
233     StringRef Name;
234   };
235 
236   // Read target features and linkage policies from module metadata
237   SmallVector<FeatureEntry, 4> EmittedFeatures;
238   for (const SubtargetFeatureKV &KV : WebAssemblyFeatureKV) {
239     std::string MDKey = (StringRef("wasm-feature-") + KV.Key).str();
240     Metadata *Policy = M.getModuleFlag(MDKey);
241     if (Policy == nullptr)
242       continue;
243 
244     FeatureEntry Entry;
245     Entry.Prefix = 0;
246     Entry.Name = KV.Key;
247 
248     if (auto *MD = cast<ConstantAsMetadata>(Policy))
249       if (auto *I = cast<ConstantInt>(MD->getValue()))
250         Entry.Prefix = I->getZExtValue();
251 
252     // Silently ignore invalid metadata
253     if (Entry.Prefix != wasm::WASM_FEATURE_PREFIX_USED &&
254         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_REQUIRED &&
255         Entry.Prefix != wasm::WASM_FEATURE_PREFIX_DISALLOWED)
256       continue;
257 
258     EmittedFeatures.push_back(Entry);
259   }
260 
261   if (EmittedFeatures.size() == 0)
262     return;
263 
264   // Emit features and linkage policies into the "target_features" section
265   MCSectionWasm *FeaturesSection = OutContext.getWasmSection(
266       ".custom_section.target_features", SectionKind::getMetadata());
267   OutStreamer->PushSection();
268   OutStreamer->SwitchSection(FeaturesSection);
269 
270   OutStreamer->EmitULEB128IntValue(EmittedFeatures.size());
271   for (auto &F : EmittedFeatures) {
272     OutStreamer->EmitIntValue(F.Prefix, 1);
273     OutStreamer->EmitULEB128IntValue(F.Name.size());
274     OutStreamer->EmitBytes(F.Name);
275   }
276 
277   OutStreamer->PopSection();
278 }
279 
EmitConstantPool()280 void WebAssemblyAsmPrinter::EmitConstantPool() {
281   assert(MF->getConstantPool()->getConstants().empty() &&
282          "WebAssembly disables constant pools");
283 }
284 
EmitJumpTableInfo()285 void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
286   // Nothing to do; jump tables are incorporated into the instruction stream.
287 }
288 
EmitFunctionBodyStart()289 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
290   const Function &F = MF->getFunction();
291   SmallVector<MVT, 1> ResultVTs;
292   SmallVector<MVT, 4> ParamVTs;
293   computeSignatureVTs(F.getFunctionType(), F, TM, ParamVTs, ResultVTs);
294   auto Signature = signatureFromMVTs(ResultVTs, ParamVTs);
295   auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
296   WasmSym->setSignature(Signature.get());
297   addSignature(std::move(Signature));
298   WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
299 
300   // FIXME: clean up how params and results are emitted (use signatures)
301   getTargetStreamer()->emitFunctionType(WasmSym);
302 
303   // Emit the function index.
304   if (MDNode *Idx = F.getMetadata("wasm.index")) {
305     assert(Idx->getNumOperands() == 1);
306 
307     getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
308         cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
309   }
310 
311   SmallVector<wasm::ValType, 16> Locals;
312   valTypesFromMVTs(MFI->getLocals(), Locals);
313   getTargetStreamer()->emitLocal(Locals);
314 
315   AsmPrinter::EmitFunctionBodyStart();
316 }
317 
EmitInstruction(const MachineInstr * MI)318 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
319   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
320 
321   switch (MI->getOpcode()) {
322   case WebAssembly::ARGUMENT_i32:
323   case WebAssembly::ARGUMENT_i32_S:
324   case WebAssembly::ARGUMENT_i64:
325   case WebAssembly::ARGUMENT_i64_S:
326   case WebAssembly::ARGUMENT_f32:
327   case WebAssembly::ARGUMENT_f32_S:
328   case WebAssembly::ARGUMENT_f64:
329   case WebAssembly::ARGUMENT_f64_S:
330   case WebAssembly::ARGUMENT_v16i8:
331   case WebAssembly::ARGUMENT_v16i8_S:
332   case WebAssembly::ARGUMENT_v8i16:
333   case WebAssembly::ARGUMENT_v8i16_S:
334   case WebAssembly::ARGUMENT_v4i32:
335   case WebAssembly::ARGUMENT_v4i32_S:
336   case WebAssembly::ARGUMENT_v2i64:
337   case WebAssembly::ARGUMENT_v2i64_S:
338   case WebAssembly::ARGUMENT_v4f32:
339   case WebAssembly::ARGUMENT_v4f32_S:
340   case WebAssembly::ARGUMENT_v2f64:
341   case WebAssembly::ARGUMENT_v2f64_S:
342     // These represent values which are live into the function entry, so there's
343     // no instruction to emit.
344     break;
345   case WebAssembly::FALLTHROUGH_RETURN: {
346     // These instructions represent the implicit return at the end of a
347     // function body.
348     if (isVerbose()) {
349       OutStreamer->AddComment("fallthrough-return");
350       OutStreamer->AddBlankLine();
351     }
352     break;
353   }
354   case WebAssembly::COMPILER_FENCE:
355     // This is a compiler barrier that prevents instruction reordering during
356     // backend compilation, and should not be emitted.
357     break;
358   case WebAssembly::EXTRACT_EXCEPTION_I32:
359   case WebAssembly::EXTRACT_EXCEPTION_I32_S:
360     // These are pseudo instructions that simulates popping values from stack.
361     // We print these only when we have -wasm-keep-registers on for assembly
362     // readability.
363     if (!WasmKeepRegisters)
364       break;
365     LLVM_FALLTHROUGH;
366   default: {
367     WebAssemblyMCInstLower MCInstLowering(OutContext, *this);
368     MCInst TmpInst;
369     MCInstLowering.lower(MI, TmpInst);
370     EmitToStreamer(*OutStreamer, TmpInst);
371     break;
372   }
373   }
374 }
375 
PrintAsmOperand(const MachineInstr * MI,unsigned OpNo,const char * ExtraCode,raw_ostream & OS)376 bool WebAssemblyAsmPrinter::PrintAsmOperand(const MachineInstr *MI,
377                                             unsigned OpNo,
378                                             const char *ExtraCode,
379                                             raw_ostream &OS) {
380   // First try the generic code, which knows about modifiers like 'c' and 'n'.
381   if (!AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, OS))
382     return false;
383 
384   if (!ExtraCode) {
385     const MachineOperand &MO = MI->getOperand(OpNo);
386     switch (MO.getType()) {
387     case MachineOperand::MO_Immediate:
388       OS << MO.getImm();
389       return false;
390     case MachineOperand::MO_Register:
391       // FIXME: only opcode that still contains registers, as required by
392       // MachineInstr::getDebugVariable().
393       assert(MI->getOpcode() == WebAssembly::INLINEASM);
394       OS << regToString(MO);
395       return false;
396     case MachineOperand::MO_GlobalAddress:
397       PrintSymbolOperand(MO, OS);
398       return false;
399     case MachineOperand::MO_ExternalSymbol:
400       GetExternalSymbolSymbol(MO.getSymbolName())->print(OS, MAI);
401       printOffset(MO.getOffset(), OS);
402       return false;
403     case MachineOperand::MO_MachineBasicBlock:
404       MO.getMBB()->getSymbol()->print(OS, MAI);
405       return false;
406     default:
407       break;
408     }
409   }
410 
411   return true;
412 }
413 
PrintAsmMemoryOperand(const MachineInstr * MI,unsigned OpNo,const char * ExtraCode,raw_ostream & OS)414 bool WebAssemblyAsmPrinter::PrintAsmMemoryOperand(const MachineInstr *MI,
415                                                   unsigned OpNo,
416                                                   const char *ExtraCode,
417                                                   raw_ostream &OS) {
418   // The current approach to inline asm is that "r" constraints are expressed
419   // as local indices, rather than values on the operand stack. This simplifies
420   // using "r" as it eliminates the need to push and pop the values in a
421   // particular order, however it also makes it impossible to have an "m"
422   // constraint. So we don't support it.
423 
424   return AsmPrinter::PrintAsmMemoryOperand(MI, OpNo, ExtraCode, OS);
425 }
426 
427 // Force static initialization.
LLVMInitializeWebAssemblyAsmPrinter()428 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyAsmPrinter() {
429   RegisterAsmPrinter<WebAssemblyAsmPrinter> X(getTheWebAssemblyTarget32());
430   RegisterAsmPrinter<WebAssemblyAsmPrinter> Y(getTheWebAssemblyTarget64());
431 }
432