xref: /freebsd/contrib/llvm-project/llvm/lib/ObjectYAML/WasmEmitter.cpp (revision 7ef62cebc2f965b0f640263e179276928885e33d) 
1 //===- yaml2wasm - Convert YAML to a Wasm object file --------------------===//
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 /// The Wasm component of yaml2obj.
11 ///
12 //===----------------------------------------------------------------------===//
13 //
14 
15 #include "llvm/Object/Wasm.h"
16 #include "llvm/ObjectYAML/ObjectYAML.h"
17 #include "llvm/ObjectYAML/yaml2obj.h"
18 #include "llvm/Support/Endian.h"
19 #include "llvm/Support/LEB128.h"
20 
21 using namespace llvm;
22 
23 namespace {
24 /// This parses a yaml stream that represents a Wasm object file.
25 /// See docs/yaml2obj for the yaml scheema.
26 class WasmWriter {
27 public:
28   WasmWriter(WasmYAML::Object &Obj, yaml::ErrorHandler EH)
29       : Obj(Obj), ErrHandler(EH) {}
30   bool writeWasm(raw_ostream &OS);
31 
32 private:
33   void writeRelocSection(raw_ostream &OS, WasmYAML::Section &Sec,
34                          uint32_t SectionIndex);
35 
36   void writeInitExpr(raw_ostream &OS, const WasmYAML::InitExpr &InitExpr);
37 
38   void writeSectionContent(raw_ostream &OS, WasmYAML::CustomSection &Section);
39   void writeSectionContent(raw_ostream &OS, WasmYAML::TypeSection &Section);
40   void writeSectionContent(raw_ostream &OS, WasmYAML::ImportSection &Section);
41   void writeSectionContent(raw_ostream &OS, WasmYAML::FunctionSection &Section);
42   void writeSectionContent(raw_ostream &OS, WasmYAML::TableSection &Section);
43   void writeSectionContent(raw_ostream &OS, WasmYAML::MemorySection &Section);
44   void writeSectionContent(raw_ostream &OS, WasmYAML::TagSection &Section);
45   void writeSectionContent(raw_ostream &OS, WasmYAML::GlobalSection &Section);
46   void writeSectionContent(raw_ostream &OS, WasmYAML::ExportSection &Section);
47   void writeSectionContent(raw_ostream &OS, WasmYAML::StartSection &Section);
48   void writeSectionContent(raw_ostream &OS, WasmYAML::ElemSection &Section);
49   void writeSectionContent(raw_ostream &OS, WasmYAML::CodeSection &Section);
50   void writeSectionContent(raw_ostream &OS, WasmYAML::DataSection &Section);
51   void writeSectionContent(raw_ostream &OS, WasmYAML::DataCountSection &Section);
52 
53   // Custom section types
54   void writeSectionContent(raw_ostream &OS, WasmYAML::DylinkSection &Section);
55   void writeSectionContent(raw_ostream &OS, WasmYAML::NameSection &Section);
56   void writeSectionContent(raw_ostream &OS, WasmYAML::LinkingSection &Section);
57   void writeSectionContent(raw_ostream &OS, WasmYAML::ProducersSection &Section);
58   void writeSectionContent(raw_ostream &OS,
59                           WasmYAML::TargetFeaturesSection &Section);
60   WasmYAML::Object &Obj;
61   uint32_t NumImportedFunctions = 0;
62   uint32_t NumImportedGlobals = 0;
63   uint32_t NumImportedTables = 0;
64   uint32_t NumImportedTags = 0;
65 
66   bool HasError = false;
67   yaml::ErrorHandler ErrHandler;
68   void reportError(const Twine &Msg);
69 };
70 
71 class SubSectionWriter {
72   raw_ostream &OS;
73   std::string OutString;
74   raw_string_ostream StringStream;
75 
76 public:
77   SubSectionWriter(raw_ostream &OS) : OS(OS), StringStream(OutString) {}
78 
79   void done() {
80     StringStream.flush();
81     encodeULEB128(OutString.size(), OS);
82     OS << OutString;
83     OutString.clear();
84   }
85 
86   raw_ostream &getStream() { return StringStream; }
87 };
88 
89 } // end anonymous namespace
90 
91 static int writeUint64(raw_ostream &OS, uint64_t Value) {
92   char Data[sizeof(Value)];
93   support::endian::write64le(Data, Value);
94   OS.write(Data, sizeof(Data));
95   return 0;
96 }
97 
98 static int writeUint32(raw_ostream &OS, uint32_t Value) {
99   char Data[sizeof(Value)];
100   support::endian::write32le(Data, Value);
101   OS.write(Data, sizeof(Data));
102   return 0;
103 }
104 
105 static int writeUint8(raw_ostream &OS, uint8_t Value) {
106   char Data[sizeof(Value)];
107   memcpy(Data, &Value, sizeof(Data));
108   OS.write(Data, sizeof(Data));
109   return 0;
110 }
111 
112 static int writeStringRef(const StringRef &Str, raw_ostream &OS) {
113   encodeULEB128(Str.size(), OS);
114   OS << Str;
115   return 0;
116 }
117 
118 static int writeLimits(const WasmYAML::Limits &Lim, raw_ostream &OS) {
119   writeUint8(OS, Lim.Flags);
120   encodeULEB128(Lim.Minimum, OS);
121   if (Lim.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX)
122     encodeULEB128(Lim.Maximum, OS);
123   return 0;
124 }
125 
126 void WasmWriter::reportError(const Twine &Msg) {
127   ErrHandler(Msg);
128   HasError = true;
129 }
130 
131 void WasmWriter::writeInitExpr(raw_ostream &OS,
132                                const WasmYAML::InitExpr &InitExpr) {
133   if (InitExpr.Extended) {
134     InitExpr.Body.writeAsBinary(OS);
135   } else {
136     writeUint8(OS, InitExpr.Inst.Opcode);
137     switch (InitExpr.Inst.Opcode) {
138     case wasm::WASM_OPCODE_I32_CONST:
139       encodeSLEB128(InitExpr.Inst.Value.Int32, OS);
140       break;
141     case wasm::WASM_OPCODE_I64_CONST:
142       encodeSLEB128(InitExpr.Inst.Value.Int64, OS);
143       break;
144     case wasm::WASM_OPCODE_F32_CONST:
145       writeUint32(OS, InitExpr.Inst.Value.Float32);
146       break;
147     case wasm::WASM_OPCODE_F64_CONST:
148       writeUint64(OS, InitExpr.Inst.Value.Float64);
149       break;
150     case wasm::WASM_OPCODE_GLOBAL_GET:
151       encodeULEB128(InitExpr.Inst.Value.Global, OS);
152       break;
153     default:
154       reportError("unknown opcode in init_expr: " +
155                   Twine(InitExpr.Inst.Opcode));
156       return;
157     }
158     writeUint8(OS, wasm::WASM_OPCODE_END);
159   }
160 }
161 
162 void WasmWriter::writeSectionContent(raw_ostream &OS,
163                                      WasmYAML::DylinkSection &Section) {
164   writeStringRef(Section.Name, OS);
165 
166   writeUint8(OS, wasm::WASM_DYLINK_MEM_INFO);
167   SubSectionWriter SubSection(OS);
168   raw_ostream &SubOS = SubSection.getStream();
169   encodeULEB128(Section.MemorySize, SubOS);
170   encodeULEB128(Section.MemoryAlignment, SubOS);
171   encodeULEB128(Section.TableSize, SubOS);
172   encodeULEB128(Section.TableAlignment, SubOS);
173   SubSection.done();
174 
175   if (Section.Needed.size()) {
176     writeUint8(OS, wasm::WASM_DYLINK_NEEDED);
177     raw_ostream &SubOS = SubSection.getStream();
178     encodeULEB128(Section.Needed.size(), SubOS);
179     for (StringRef Needed : Section.Needed)
180       writeStringRef(Needed, SubOS);
181     SubSection.done();
182   }
183 }
184 
185 void WasmWriter::writeSectionContent(raw_ostream &OS,
186                                      WasmYAML::LinkingSection &Section) {
187   writeStringRef(Section.Name, OS);
188   encodeULEB128(Section.Version, OS);
189 
190   SubSectionWriter SubSection(OS);
191 
192   // SYMBOL_TABLE subsection
193   if (Section.SymbolTable.size()) {
194     writeUint8(OS, wasm::WASM_SYMBOL_TABLE);
195     encodeULEB128(Section.SymbolTable.size(), SubSection.getStream());
196     for (auto Sym : llvm::enumerate(Section.SymbolTable)) {
197       const WasmYAML::SymbolInfo &Info = Sym.value();
198       assert(Info.Index == Sym.index());
199       writeUint8(SubSection.getStream(), Info.Kind);
200       encodeULEB128(Info.Flags, SubSection.getStream());
201       switch (Info.Kind) {
202       case wasm::WASM_SYMBOL_TYPE_FUNCTION:
203       case wasm::WASM_SYMBOL_TYPE_GLOBAL:
204       case wasm::WASM_SYMBOL_TYPE_TABLE:
205       case wasm::WASM_SYMBOL_TYPE_TAG:
206         encodeULEB128(Info.ElementIndex, SubSection.getStream());
207         if ((Info.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 ||
208             (Info.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0)
209           writeStringRef(Info.Name, SubSection.getStream());
210         break;
211       case wasm::WASM_SYMBOL_TYPE_DATA:
212         writeStringRef(Info.Name, SubSection.getStream());
213         if ((Info.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) {
214           encodeULEB128(Info.DataRef.Segment, SubSection.getStream());
215           encodeULEB128(Info.DataRef.Offset, SubSection.getStream());
216           encodeULEB128(Info.DataRef.Size, SubSection.getStream());
217         }
218         break;
219       case wasm::WASM_SYMBOL_TYPE_SECTION:
220         encodeULEB128(Info.ElementIndex, SubSection.getStream());
221         break;
222       default:
223         llvm_unreachable("unexpected kind");
224       }
225     }
226 
227     SubSection.done();
228   }
229 
230   // SEGMENT_NAMES subsection
231   if (Section.SegmentInfos.size()) {
232     writeUint8(OS, wasm::WASM_SEGMENT_INFO);
233     encodeULEB128(Section.SegmentInfos.size(), SubSection.getStream());
234     for (const WasmYAML::SegmentInfo &SegmentInfo : Section.SegmentInfos) {
235       writeStringRef(SegmentInfo.Name, SubSection.getStream());
236       encodeULEB128(SegmentInfo.Alignment, SubSection.getStream());
237       encodeULEB128(SegmentInfo.Flags, SubSection.getStream());
238     }
239     SubSection.done();
240   }
241 
242   // INIT_FUNCS subsection
243   if (Section.InitFunctions.size()) {
244     writeUint8(OS, wasm::WASM_INIT_FUNCS);
245     encodeULEB128(Section.InitFunctions.size(), SubSection.getStream());
246     for (const WasmYAML::InitFunction &Func : Section.InitFunctions) {
247       encodeULEB128(Func.Priority, SubSection.getStream());
248       encodeULEB128(Func.Symbol, SubSection.getStream());
249     }
250     SubSection.done();
251   }
252 
253   // COMDAT_INFO subsection
254   if (Section.Comdats.size()) {
255     writeUint8(OS, wasm::WASM_COMDAT_INFO);
256     encodeULEB128(Section.Comdats.size(), SubSection.getStream());
257     for (const auto &C : Section.Comdats) {
258       writeStringRef(C.Name, SubSection.getStream());
259       encodeULEB128(0, SubSection.getStream()); // flags for future use
260       encodeULEB128(C.Entries.size(), SubSection.getStream());
261       for (const WasmYAML::ComdatEntry &Entry : C.Entries) {
262         writeUint8(SubSection.getStream(), Entry.Kind);
263         encodeULEB128(Entry.Index, SubSection.getStream());
264       }
265     }
266     SubSection.done();
267   }
268 }
269 
270 void WasmWriter::writeSectionContent(raw_ostream &OS,
271                                      WasmYAML::NameSection &Section) {
272   writeStringRef(Section.Name, OS);
273   if (Section.FunctionNames.size()) {
274     writeUint8(OS, wasm::WASM_NAMES_FUNCTION);
275 
276     SubSectionWriter SubSection(OS);
277 
278     encodeULEB128(Section.FunctionNames.size(), SubSection.getStream());
279     for (const WasmYAML::NameEntry &NameEntry : Section.FunctionNames) {
280       encodeULEB128(NameEntry.Index, SubSection.getStream());
281       writeStringRef(NameEntry.Name, SubSection.getStream());
282     }
283 
284     SubSection.done();
285   }
286   if (Section.GlobalNames.size()) {
287     writeUint8(OS, wasm::WASM_NAMES_GLOBAL);
288 
289     SubSectionWriter SubSection(OS);
290 
291     encodeULEB128(Section.GlobalNames.size(), SubSection.getStream());
292     for (const WasmYAML::NameEntry &NameEntry : Section.GlobalNames) {
293       encodeULEB128(NameEntry.Index, SubSection.getStream());
294       writeStringRef(NameEntry.Name, SubSection.getStream());
295     }
296 
297     SubSection.done();
298   }
299   if (Section.DataSegmentNames.size()) {
300     writeUint8(OS, wasm::WASM_NAMES_DATA_SEGMENT);
301 
302     SubSectionWriter SubSection(OS);
303 
304     encodeULEB128(Section.DataSegmentNames.size(), SubSection.getStream());
305     for (const WasmYAML::NameEntry &NameEntry : Section.DataSegmentNames) {
306       encodeULEB128(NameEntry.Index, SubSection.getStream());
307       writeStringRef(NameEntry.Name, SubSection.getStream());
308     }
309 
310     SubSection.done();
311   }
312 }
313 
314 void WasmWriter::writeSectionContent(raw_ostream &OS,
315                                      WasmYAML::ProducersSection &Section) {
316   writeStringRef(Section.Name, OS);
317   int Fields = int(!Section.Languages.empty()) + int(!Section.Tools.empty()) +
318                int(!Section.SDKs.empty());
319   if (Fields == 0)
320     return;
321   encodeULEB128(Fields, OS);
322   for (auto &Field : {std::make_pair(StringRef("language"), &Section.Languages),
323                       std::make_pair(StringRef("processed-by"), &Section.Tools),
324                       std::make_pair(StringRef("sdk"), &Section.SDKs)}) {
325     if (Field.second->empty())
326       continue;
327     writeStringRef(Field.first, OS);
328     encodeULEB128(Field.second->size(), OS);
329     for (auto &Entry : *Field.second) {
330       writeStringRef(Entry.Name, OS);
331       writeStringRef(Entry.Version, OS);
332     }
333   }
334 }
335 
336 void WasmWriter::writeSectionContent(raw_ostream &OS,
337                                      WasmYAML::TargetFeaturesSection &Section) {
338   writeStringRef(Section.Name, OS);
339   encodeULEB128(Section.Features.size(), OS);
340   for (auto &E : Section.Features) {
341     writeUint8(OS, E.Prefix);
342     writeStringRef(E.Name, OS);
343   }
344 }
345 
346 void WasmWriter::writeSectionContent(raw_ostream &OS,
347                                      WasmYAML::CustomSection &Section) {
348   if (auto S = dyn_cast<WasmYAML::DylinkSection>(&Section)) {
349     writeSectionContent(OS, *S);
350   } else if (auto S = dyn_cast<WasmYAML::NameSection>(&Section)) {
351     writeSectionContent(OS, *S);
352   } else if (auto S = dyn_cast<WasmYAML::LinkingSection>(&Section)) {
353     writeSectionContent(OS, *S);
354   } else if (auto S = dyn_cast<WasmYAML::ProducersSection>(&Section)) {
355     writeSectionContent(OS, *S);
356   } else if (auto S = dyn_cast<WasmYAML::TargetFeaturesSection>(&Section)) {
357     writeSectionContent(OS, *S);
358   } else {
359     writeStringRef(Section.Name, OS);
360     Section.Payload.writeAsBinary(OS);
361   }
362 }
363 
364 void WasmWriter::writeSectionContent(raw_ostream &OS,
365                                     WasmYAML::TypeSection &Section) {
366   encodeULEB128(Section.Signatures.size(), OS);
367   uint32_t ExpectedIndex = 0;
368   for (const WasmYAML::Signature &Sig : Section.Signatures) {
369     if (Sig.Index != ExpectedIndex) {
370       reportError("unexpected type index: " + Twine(Sig.Index));
371       return;
372     }
373     ++ExpectedIndex;
374     writeUint8(OS, Sig.Form);
375     encodeULEB128(Sig.ParamTypes.size(), OS);
376     for (auto ParamType : Sig.ParamTypes)
377       writeUint8(OS, ParamType);
378     encodeULEB128(Sig.ReturnTypes.size(), OS);
379     for (auto ReturnType : Sig.ReturnTypes)
380       writeUint8(OS, ReturnType);
381   }
382 }
383 
384 void WasmWriter::writeSectionContent(raw_ostream &OS,
385                                     WasmYAML::ImportSection &Section) {
386   encodeULEB128(Section.Imports.size(), OS);
387   for (const WasmYAML::Import &Import : Section.Imports) {
388     writeStringRef(Import.Module, OS);
389     writeStringRef(Import.Field, OS);
390     writeUint8(OS, Import.Kind);
391     switch (Import.Kind) {
392     case wasm::WASM_EXTERNAL_FUNCTION:
393       encodeULEB128(Import.SigIndex, OS);
394       NumImportedFunctions++;
395       break;
396     case wasm::WASM_EXTERNAL_GLOBAL:
397       writeUint8(OS, Import.GlobalImport.Type);
398       writeUint8(OS, Import.GlobalImport.Mutable);
399       NumImportedGlobals++;
400       break;
401     case wasm::WASM_EXTERNAL_TAG:
402       writeUint8(OS, 0); // Reserved 'attribute' field
403       encodeULEB128(Import.SigIndex, OS);
404       NumImportedTags++;
405       break;
406     case wasm::WASM_EXTERNAL_MEMORY:
407       writeLimits(Import.Memory, OS);
408       break;
409     case wasm::WASM_EXTERNAL_TABLE:
410       writeUint8(OS, Import.TableImport.ElemType);
411       writeLimits(Import.TableImport.TableLimits, OS);
412       NumImportedTables++;
413       break;
414     default:
415       reportError("unknown import type: " +Twine(Import.Kind));
416       return;
417     }
418   }
419 }
420 
421 void WasmWriter::writeSectionContent(raw_ostream &OS,
422                                      WasmYAML::FunctionSection &Section) {
423   encodeULEB128(Section.FunctionTypes.size(), OS);
424   for (uint32_t FuncType : Section.FunctionTypes)
425     encodeULEB128(FuncType, OS);
426 }
427 
428 void WasmWriter::writeSectionContent(raw_ostream &OS,
429                                     WasmYAML::ExportSection &Section) {
430   encodeULEB128(Section.Exports.size(), OS);
431   for (const WasmYAML::Export &Export : Section.Exports) {
432     writeStringRef(Export.Name, OS);
433     writeUint8(OS, Export.Kind);
434     encodeULEB128(Export.Index, OS);
435   }
436 }
437 
438 void WasmWriter::writeSectionContent(raw_ostream &OS,
439                                      WasmYAML::StartSection &Section) {
440   encodeULEB128(Section.StartFunction, OS);
441 }
442 
443 void WasmWriter::writeSectionContent(raw_ostream &OS,
444                                      WasmYAML::TableSection &Section) {
445   encodeULEB128(Section.Tables.size(), OS);
446   uint32_t ExpectedIndex = NumImportedTables;
447   for (auto &Table : Section.Tables) {
448     if (Table.Index != ExpectedIndex) {
449       reportError("unexpected table index: " + Twine(Table.Index));
450       return;
451     }
452     ++ExpectedIndex;
453     writeUint8(OS, Table.ElemType);
454     writeLimits(Table.TableLimits, OS);
455   }
456 }
457 
458 void WasmWriter::writeSectionContent(raw_ostream &OS,
459                                      WasmYAML::MemorySection &Section) {
460   encodeULEB128(Section.Memories.size(), OS);
461   for (const WasmYAML::Limits &Mem : Section.Memories)
462     writeLimits(Mem, OS);
463 }
464 
465 void WasmWriter::writeSectionContent(raw_ostream &OS,
466                                      WasmYAML::TagSection &Section) {
467   encodeULEB128(Section.TagTypes.size(), OS);
468   for (uint32_t TagType : Section.TagTypes) {
469     writeUint8(OS, 0); // Reserved 'attribute' field
470     encodeULEB128(TagType, OS);
471   }
472 }
473 
474 void WasmWriter::writeSectionContent(raw_ostream &OS,
475                                      WasmYAML::GlobalSection &Section) {
476   encodeULEB128(Section.Globals.size(), OS);
477   uint32_t ExpectedIndex = NumImportedGlobals;
478   for (auto &Global : Section.Globals) {
479     if (Global.Index != ExpectedIndex) {
480       reportError("unexpected global index: " + Twine(Global.Index));
481       return;
482     }
483     ++ExpectedIndex;
484     writeUint8(OS, Global.Type);
485     writeUint8(OS, Global.Mutable);
486     writeInitExpr(OS, Global.Init);
487   }
488 }
489 
490 void WasmWriter::writeSectionContent(raw_ostream &OS,
491                                      WasmYAML::ElemSection &Section) {
492   encodeULEB128(Section.Segments.size(), OS);
493   for (auto &Segment : Section.Segments) {
494     encodeULEB128(Segment.Flags, OS);
495     if (Segment.Flags & wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER)
496       encodeULEB128(Segment.TableNumber, OS);
497 
498     writeInitExpr(OS, Segment.Offset);
499 
500     if (Segment.Flags & wasm::WASM_ELEM_SEGMENT_MASK_HAS_ELEM_KIND) {
501       // We only support active function table initializers, for which the elem
502       // kind is specified to be written as 0x00 and interpreted to mean
503       // "funcref".
504       if (Segment.ElemKind != uint32_t(wasm::ValType::FUNCREF)) {
505         reportError("unexpected elemkind: " + Twine(Segment.ElemKind));
506         return;
507       }
508       const uint8_t ElemKind = 0;
509       writeUint8(OS, ElemKind);
510     }
511 
512     encodeULEB128(Segment.Functions.size(), OS);
513     for (auto &Function : Segment.Functions)
514       encodeULEB128(Function, OS);
515   }
516 }
517 
518 void WasmWriter::writeSectionContent(raw_ostream &OS,
519                                     WasmYAML::CodeSection &Section) {
520   encodeULEB128(Section.Functions.size(), OS);
521   uint32_t ExpectedIndex = NumImportedFunctions;
522   for (auto &Func : Section.Functions) {
523     std::string OutString;
524     raw_string_ostream StringStream(OutString);
525     if (Func.Index != ExpectedIndex) {
526       reportError("unexpected function index: " + Twine(Func.Index));
527       return;
528     }
529     ++ExpectedIndex;
530 
531     encodeULEB128(Func.Locals.size(), StringStream);
532     for (auto &LocalDecl : Func.Locals) {
533       encodeULEB128(LocalDecl.Count, StringStream);
534       writeUint8(StringStream, LocalDecl.Type);
535     }
536 
537     Func.Body.writeAsBinary(StringStream);
538 
539     // Write the section size followed by the content
540     StringStream.flush();
541     encodeULEB128(OutString.size(), OS);
542     OS << OutString;
543   }
544 }
545 
546 void WasmWriter::writeSectionContent(raw_ostream &OS,
547                                      WasmYAML::DataSection &Section) {
548   encodeULEB128(Section.Segments.size(), OS);
549   for (auto &Segment : Section.Segments) {
550     encodeULEB128(Segment.InitFlags, OS);
551     if (Segment.InitFlags & wasm::WASM_DATA_SEGMENT_HAS_MEMINDEX)
552       encodeULEB128(Segment.MemoryIndex, OS);
553     if ((Segment.InitFlags & wasm::WASM_DATA_SEGMENT_IS_PASSIVE) == 0)
554       writeInitExpr(OS, Segment.Offset);
555     encodeULEB128(Segment.Content.binary_size(), OS);
556     Segment.Content.writeAsBinary(OS);
557   }
558 }
559 
560 void WasmWriter::writeSectionContent(raw_ostream &OS,
561                                      WasmYAML::DataCountSection &Section) {
562   encodeULEB128(Section.Count, OS);
563 }
564 
565 void WasmWriter::writeRelocSection(raw_ostream &OS, WasmYAML::Section &Sec,
566                                   uint32_t SectionIndex) {
567   switch (Sec.Type) {
568   case wasm::WASM_SEC_CODE:
569     writeStringRef("reloc.CODE", OS);
570     break;
571   case wasm::WASM_SEC_DATA:
572     writeStringRef("reloc.DATA", OS);
573     break;
574   case wasm::WASM_SEC_CUSTOM: {
575     auto *CustomSection = cast<WasmYAML::CustomSection>(&Sec);
576     writeStringRef(("reloc." + CustomSection->Name).str(), OS);
577     break;
578   }
579   default:
580     llvm_unreachable("not yet implemented");
581   }
582 
583   encodeULEB128(SectionIndex, OS);
584   encodeULEB128(Sec.Relocations.size(), OS);
585 
586   for (auto Reloc : Sec.Relocations) {
587     writeUint8(OS, Reloc.Type);
588     encodeULEB128(Reloc.Offset, OS);
589     encodeULEB128(Reloc.Index, OS);
590     if (wasm::relocTypeHasAddend(Reloc.Type))
591       encodeSLEB128(Reloc.Addend, OS);
592   }
593 }
594 
595 bool WasmWriter::writeWasm(raw_ostream &OS) {
596   // Write headers
597   OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic));
598   writeUint32(OS, Obj.Header.Version);
599 
600   // Write each section
601   llvm::object::WasmSectionOrderChecker Checker;
602   for (const std::unique_ptr<WasmYAML::Section> &Sec : Obj.Sections) {
603     StringRef SecName = "";
604     if (auto S = dyn_cast<WasmYAML::CustomSection>(Sec.get()))
605       SecName = S->Name;
606     if (!Checker.isValidSectionOrder(Sec->Type, SecName)) {
607       reportError("out of order section type: " + Twine(Sec->Type));
608       return false;
609     }
610     encodeULEB128(Sec->Type, OS);
611     std::string OutString;
612     raw_string_ostream StringStream(OutString);
613     if (auto S = dyn_cast<WasmYAML::CustomSection>(Sec.get()))
614       writeSectionContent(StringStream, *S);
615     else if (auto S = dyn_cast<WasmYAML::TypeSection>(Sec.get()))
616       writeSectionContent(StringStream, *S);
617     else if (auto S = dyn_cast<WasmYAML::ImportSection>(Sec.get()))
618       writeSectionContent(StringStream, *S);
619     else if (auto S = dyn_cast<WasmYAML::FunctionSection>(Sec.get()))
620       writeSectionContent(StringStream, *S);
621     else if (auto S = dyn_cast<WasmYAML::TableSection>(Sec.get()))
622       writeSectionContent(StringStream, *S);
623     else if (auto S = dyn_cast<WasmYAML::MemorySection>(Sec.get()))
624       writeSectionContent(StringStream, *S);
625     else if (auto S = dyn_cast<WasmYAML::TagSection>(Sec.get()))
626       writeSectionContent(StringStream, *S);
627     else if (auto S = dyn_cast<WasmYAML::GlobalSection>(Sec.get()))
628       writeSectionContent(StringStream, *S);
629     else if (auto S = dyn_cast<WasmYAML::ExportSection>(Sec.get()))
630       writeSectionContent(StringStream, *S);
631     else if (auto S = dyn_cast<WasmYAML::StartSection>(Sec.get()))
632       writeSectionContent(StringStream, *S);
633     else if (auto S = dyn_cast<WasmYAML::ElemSection>(Sec.get()))
634       writeSectionContent(StringStream, *S);
635     else if (auto S = dyn_cast<WasmYAML::CodeSection>(Sec.get()))
636       writeSectionContent(StringStream, *S);
637     else if (auto S = dyn_cast<WasmYAML::DataSection>(Sec.get()))
638       writeSectionContent(StringStream, *S);
639     else if (auto S = dyn_cast<WasmYAML::DataCountSection>(Sec.get()))
640       writeSectionContent(StringStream, *S);
641     else
642       reportError("unknown section type: " + Twine(Sec->Type));
643 
644     if (HasError)
645       return false;
646 
647     StringStream.flush();
648 
649     // Write the section size followed by the content
650     encodeULEB128(OutString.size(), OS);
651     OS << OutString;
652   }
653 
654   // write reloc sections for any section that have relocations
655   uint32_t SectionIndex = 0;
656   for (const std::unique_ptr<WasmYAML::Section> &Sec : Obj.Sections) {
657     if (Sec->Relocations.empty()) {
658       SectionIndex++;
659       continue;
660     }
661 
662     writeUint8(OS, wasm::WASM_SEC_CUSTOM);
663     std::string OutString;
664     raw_string_ostream StringStream(OutString);
665     writeRelocSection(StringStream, *Sec, SectionIndex++);
666     StringStream.flush();
667 
668     encodeULEB128(OutString.size(), OS);
669     OS << OutString;
670   }
671 
672   return true;
673 }
674 
675 namespace llvm {
676 namespace yaml {
677 
678 bool yaml2wasm(WasmYAML::Object &Doc, raw_ostream &Out, ErrorHandler EH) {
679   WasmWriter Writer(Doc, EH);
680   return Writer.writeWasm(Out);
681 }
682 
683 } // namespace yaml
684 } // namespace llvm
685