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comparison lib/MC/WasmObjectWriter.cpp @ 121:803732b1fca8

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LLVM 5.0
author kono
date Fri, 27 Oct 2017 17:07:41 +0900
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120:1172e4bd9c6f 121:803732b1fca8
1 //===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements Wasm object file writer information.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/ADT/STLExtras.h"
15 #include "llvm/ADT/SmallPtrSet.h"
16 #include "llvm/BinaryFormat/Wasm.h"
17 #include "llvm/MC/MCAsmBackend.h"
18 #include "llvm/MC/MCAsmInfo.h"
19 #include "llvm/MC/MCAsmLayout.h"
20 #include "llvm/MC/MCAssembler.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCFixupKindInfo.h"
24 #include "llvm/MC/MCObjectFileInfo.h"
25 #include "llvm/MC/MCObjectWriter.h"
26 #include "llvm/MC/MCSectionWasm.h"
27 #include "llvm/MC/MCSymbolWasm.h"
28 #include "llvm/MC/MCValue.h"
29 #include "llvm/MC/MCWasmObjectWriter.h"
30 #include "llvm/Support/Casting.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/ErrorHandling.h"
33 #include "llvm/Support/LEB128.h"
34 #include "llvm/Support/StringSaver.h"
35 #include <vector>
36
37 using namespace llvm;
38
39 #define DEBUG_TYPE "mc"
40
41 namespace {
42
43 // For patching purposes, we need to remember where each section starts, both
44 // for patching up the section size field, and for patching up references to
45 // locations within the section.
46 struct SectionBookkeeping {
47 // Where the size of the section is written.
48 uint64_t SizeOffset;
49 // Where the contents of the section starts (after the header).
50 uint64_t ContentsOffset;
51 };
52
53 // The signature of a wasm function, in a struct capable of being used as a
54 // DenseMap key.
55 struct WasmFunctionType {
56 // Support empty and tombstone instances, needed by DenseMap.
57 enum { Plain, Empty, Tombstone } State;
58
59 // The return types of the function.
60 SmallVector<wasm::ValType, 1> Returns;
61
62 // The parameter types of the function.
63 SmallVector<wasm::ValType, 4> Params;
64
65 WasmFunctionType() : State(Plain) {}
66
67 bool operator==(const WasmFunctionType &Other) const {
68 return State == Other.State && Returns == Other.Returns &&
69 Params == Other.Params;
70 }
71 };
72
73 // Traits for using WasmFunctionType in a DenseMap.
74 struct WasmFunctionTypeDenseMapInfo {
75 static WasmFunctionType getEmptyKey() {
76 WasmFunctionType FuncTy;
77 FuncTy.State = WasmFunctionType::Empty;
78 return FuncTy;
79 }
80 static WasmFunctionType getTombstoneKey() {
81 WasmFunctionType FuncTy;
82 FuncTy.State = WasmFunctionType::Tombstone;
83 return FuncTy;
84 }
85 static unsigned getHashValue(const WasmFunctionType &FuncTy) {
86 uintptr_t Value = FuncTy.State;
87 for (wasm::ValType Ret : FuncTy.Returns)
88 Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Ret));
89 for (wasm::ValType Param : FuncTy.Params)
90 Value += DenseMapInfo<int32_t>::getHashValue(int32_t(Param));
91 return Value;
92 }
93 static bool isEqual(const WasmFunctionType &LHS,
94 const WasmFunctionType &RHS) {
95 return LHS == RHS;
96 }
97 };
98
99 // A wasm data segment. A wasm binary contains only a single data section
100 // but that can contain many segments, each with their own virtual location
101 // in memory. Each MCSection data created by llvm is modeled as its own
102 // wasm data segment.
103 struct WasmDataSegment {
104 MCSectionWasm *Section;
105 StringRef Name;
106 uint32_t Offset;
107 uint32_t Alignment;
108 uint32_t Flags;
109 SmallVector<char, 4> Data;
110 };
111
112 // A wasm import to be written into the import section.
113 struct WasmImport {
114 StringRef ModuleName;
115 StringRef FieldName;
116 unsigned Kind;
117 int32_t Type;
118 };
119
120 // A wasm function to be written into the function section.
121 struct WasmFunction {
122 int32_t Type;
123 const MCSymbolWasm *Sym;
124 };
125
126 // A wasm export to be written into the export section.
127 struct WasmExport {
128 StringRef FieldName;
129 unsigned Kind;
130 uint32_t Index;
131 };
132
133 // A wasm global to be written into the global section.
134 struct WasmGlobal {
135 wasm::ValType Type;
136 bool IsMutable;
137 bool HasImport;
138 uint64_t InitialValue;
139 uint32_t ImportIndex;
140 };
141
142 // Information about a single relocation.
143 struct WasmRelocationEntry {
144 uint64_t Offset; // Where is the relocation.
145 const MCSymbolWasm *Symbol; // The symbol to relocate with.
146 int64_t Addend; // A value to add to the symbol.
147 unsigned Type; // The type of the relocation.
148 const MCSectionWasm *FixupSection;// The section the relocation is targeting.
149
150 WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol,
151 int64_t Addend, unsigned Type,
152 const MCSectionWasm *FixupSection)
153 : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type),
154 FixupSection(FixupSection) {}
155
156 bool hasAddend() const {
157 switch (Type) {
158 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
159 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
160 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
161 return true;
162 default:
163 return false;
164 }
165 }
166
167 void print(raw_ostream &Out) const {
168 Out << "Off=" << Offset << ", Sym=" << *Symbol << ", Addend=" << Addend
169 << ", Type=" << Type
170 << ", FixupSection=" << FixupSection->getSectionName();
171 }
172
173 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
174 LLVM_DUMP_METHOD void dump() const { print(dbgs()); }
175 #endif
176 };
177
178 #if !defined(NDEBUG)
179 raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) {
180 Rel.print(OS);
181 return OS;
182 }
183 #endif
184
185 class WasmObjectWriter : public MCObjectWriter {
186 /// Helper struct for containing some precomputed information on symbols.
187 struct WasmSymbolData {
188 const MCSymbolWasm *Symbol;
189 StringRef Name;
190
191 // Support lexicographic sorting.
192 bool operator<(const WasmSymbolData &RHS) const { return Name < RHS.Name; }
193 };
194
195 /// The target specific Wasm writer instance.
196 std::unique_ptr<MCWasmObjectTargetWriter> TargetObjectWriter;
197
198 // Relocations for fixing up references in the code section.
199 std::vector<WasmRelocationEntry> CodeRelocations;
200
201 // Relocations for fixing up references in the data section.
202 std::vector<WasmRelocationEntry> DataRelocations;
203
204 // Index values to use for fixing up call_indirect type indices.
205 // Maps function symbols to the index of the type of the function
206 DenseMap<const MCSymbolWasm *, uint32_t> TypeIndices;
207 // Maps function symbols to the table element index space. Used
208 // for TABLE_INDEX relocation types (i.e. address taken functions).
209 DenseMap<const MCSymbolWasm *, uint32_t> IndirectSymbolIndices;
210 // Maps function/global symbols to the function/global index space.
211 DenseMap<const MCSymbolWasm *, uint32_t> SymbolIndices;
212
213 DenseMap<WasmFunctionType, int32_t, WasmFunctionTypeDenseMapInfo>
214 FunctionTypeIndices;
215 SmallVector<WasmFunctionType, 4> FunctionTypes;
216 SmallVector<WasmGlobal, 4> Globals;
217 unsigned NumGlobalImports = 0;
218
219 // TargetObjectWriter wrappers.
220 bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
221 unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup) const {
222 return TargetObjectWriter->getRelocType(Target, Fixup);
223 }
224
225 void startSection(SectionBookkeeping &Section, unsigned SectionId,
226 const char *Name = nullptr);
227 void endSection(SectionBookkeeping &Section);
228
229 public:
230 WasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
231 raw_pwrite_stream &OS)
232 : MCObjectWriter(OS, /*IsLittleEndian=*/true),
233 TargetObjectWriter(std::move(MOTW)) {}
234
235 private:
236 ~WasmObjectWriter() override;
237
238 void reset() override {
239 CodeRelocations.clear();
240 DataRelocations.clear();
241 TypeIndices.clear();
242 SymbolIndices.clear();
243 IndirectSymbolIndices.clear();
244 FunctionTypeIndices.clear();
245 FunctionTypes.clear();
246 Globals.clear();
247 MCObjectWriter::reset();
248 NumGlobalImports = 0;
249 }
250
251 void writeHeader(const MCAssembler &Asm);
252
253 void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
254 const MCFragment *Fragment, const MCFixup &Fixup,
255 MCValue Target, uint64_t &FixedValue) override;
256
257 void executePostLayoutBinding(MCAssembler &Asm,
258 const MCAsmLayout &Layout) override;
259
260 void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
261
262 void writeString(const StringRef Str) {
263 encodeULEB128(Str.size(), getStream());
264 writeBytes(Str);
265 }
266
267 void writeValueType(wasm::ValType Ty) {
268 encodeSLEB128(int32_t(Ty), getStream());
269 }
270
271 void writeTypeSection(ArrayRef<WasmFunctionType> FunctionTypes);
272 void writeImportSection(ArrayRef<WasmImport> Imports);
273 void writeFunctionSection(ArrayRef<WasmFunction> Functions);
274 void writeTableSection(uint32_t NumElements);
275 void writeMemorySection(uint32_t DataSize);
276 void writeGlobalSection();
277 void writeExportSection(ArrayRef<WasmExport> Exports);
278 void writeElemSection(ArrayRef<uint32_t> TableElems);
279 void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
280 ArrayRef<WasmFunction> Functions);
281 void writeDataSection(ArrayRef<WasmDataSegment> Segments);
282 void writeNameSection(ArrayRef<WasmFunction> Functions,
283 ArrayRef<WasmImport> Imports,
284 uint32_t NumFuncImports);
285 void writeCodeRelocSection();
286 void writeDataRelocSection();
287 void writeLinkingMetaDataSection(
288 ArrayRef<WasmDataSegment> Segments, uint32_t DataSize,
289 SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags,
290 bool HasStackPointer, uint32_t StackPointerGlobal);
291
292 uint32_t getProvisionalValue(const WasmRelocationEntry &RelEntry);
293 void applyRelocations(ArrayRef<WasmRelocationEntry> Relocations,
294 uint64_t ContentsOffset);
295
296 void writeRelocations(ArrayRef<WasmRelocationEntry> Relocations);
297 uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry);
298 uint32_t getFunctionType(const MCSymbolWasm& Symbol);
299 uint32_t registerFunctionType(const MCSymbolWasm& Symbol);
300 };
301
302 } // end anonymous namespace
303
304 WasmObjectWriter::~WasmObjectWriter() {}
305
306 // Write out a section header and a patchable section size field.
307 void WasmObjectWriter::startSection(SectionBookkeeping &Section,
308 unsigned SectionId,
309 const char *Name) {
310 assert((Name != nullptr) == (SectionId == wasm::WASM_SEC_CUSTOM) &&
311 "Only custom sections can have names");
312
313 DEBUG(dbgs() << "startSection " << SectionId << ": " << Name << "\n");
314 encodeULEB128(SectionId, getStream());
315
316 Section.SizeOffset = getStream().tell();
317
318 // The section size. We don't know the size yet, so reserve enough space
319 // for any 32-bit value; we'll patch it later.
320 encodeULEB128(UINT32_MAX, getStream());
321
322 // The position where the section starts, for measuring its size.
323 Section.ContentsOffset = getStream().tell();
324
325 // Custom sections in wasm also have a string identifier.
326 if (SectionId == wasm::WASM_SEC_CUSTOM) {
327 assert(Name);
328 writeString(StringRef(Name));
329 }
330 }
331
332 // Now that the section is complete and we know how big it is, patch up the
333 // section size field at the start of the section.
334 void WasmObjectWriter::endSection(SectionBookkeeping &Section) {
335 uint64_t Size = getStream().tell() - Section.ContentsOffset;
336 if (uint32_t(Size) != Size)
337 report_fatal_error("section size does not fit in a uint32_t");
338
339 DEBUG(dbgs() << "endSection size=" << Size << "\n");
340
341 // Write the final section size to the payload_len field, which follows
342 // the section id byte.
343 uint8_t Buffer[16];
344 unsigned SizeLen = encodeULEB128(Size, Buffer, 5);
345 assert(SizeLen == 5);
346 getStream().pwrite((char *)Buffer, SizeLen, Section.SizeOffset);
347 }
348
349 // Emit the Wasm header.
350 void WasmObjectWriter::writeHeader(const MCAssembler &Asm) {
351 writeBytes(StringRef(wasm::WasmMagic, sizeof(wasm::WasmMagic)));
352 writeLE32(wasm::WasmVersion);
353 }
354
355 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
356 const MCAsmLayout &Layout) {
357 }
358
359 void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
360 const MCAsmLayout &Layout,
361 const MCFragment *Fragment,
362 const MCFixup &Fixup, MCValue Target,
363 uint64_t &FixedValue) {
364 MCAsmBackend &Backend = Asm.getBackend();
365 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
366 MCFixupKindInfo::FKF_IsPCRel;
367 const auto &FixupSection = cast<MCSectionWasm>(*Fragment->getParent());
368 uint64_t C = Target.getConstant();
369 uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
370 MCContext &Ctx = Asm.getContext();
371
372 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
373 assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
374 "Should not have constructed this");
375
376 // Let A, B and C being the components of Target and R be the location of
377 // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
378 // If it is pcrel, we want to compute (A - B + C - R).
379
380 // In general, Wasm has no relocations for -B. It can only represent (A + C)
381 // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
382 // replace B to implement it: (A - R - K + C)
383 if (IsPCRel) {
384 Ctx.reportError(
385 Fixup.getLoc(),
386 "No relocation available to represent this relative expression");
387 return;
388 }
389
390 const auto &SymB = cast<MCSymbolWasm>(RefB->getSymbol());
391
392 if (SymB.isUndefined()) {
393 Ctx.reportError(Fixup.getLoc(),
394 Twine("symbol '") + SymB.getName() +
395 "' can not be undefined in a subtraction expression");
396 return;
397 }
398
399 assert(!SymB.isAbsolute() && "Should have been folded");
400 const MCSection &SecB = SymB.getSection();
401 if (&SecB != &FixupSection) {
402 Ctx.reportError(Fixup.getLoc(),
403 "Cannot represent a difference across sections");
404 return;
405 }
406
407 uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
408 uint64_t K = SymBOffset - FixupOffset;
409 IsPCRel = true;
410 C -= K;
411 }
412
413 // We either rejected the fixup or folded B into C at this point.
414 const MCSymbolRefExpr *RefA = Target.getSymA();
415 const auto *SymA = RefA ? cast<MCSymbolWasm>(&RefA->getSymbol()) : nullptr;
416
417 if (SymA && SymA->isVariable()) {
418 const MCExpr *Expr = SymA->getVariableValue();
419 const auto *Inner = cast<MCSymbolRefExpr>(Expr);
420 if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
421 llvm_unreachable("weakref used in reloc not yet implemented");
422 }
423
424 // Put any constant offset in an addend. Offsets can be negative, and
425 // LLVM expects wrapping, in contrast to wasm's immediates which can't
426 // be negative and don't wrap.
427 FixedValue = 0;
428
429 if (SymA)
430 SymA->setUsedInReloc();
431
432 assert(!IsPCRel);
433 assert(SymA);
434
435 unsigned Type = getRelocType(Target, Fixup);
436
437 WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
438 DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");
439
440 if (FixupSection.isWasmData())
441 DataRelocations.push_back(Rec);
442 else if (FixupSection.getKind().isText())
443 CodeRelocations.push_back(Rec);
444 else if (!FixupSection.getKind().isMetadata())
445 // TODO(sbc): Add support for debug sections.
446 llvm_unreachable("unexpected section type");
447 }
448
449 // Write X as an (unsigned) LEB value at offset Offset in Stream, padded
450 // to allow patching.
451 static void
452 WritePatchableLEB(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
453 uint8_t Buffer[5];
454 unsigned SizeLen = encodeULEB128(X, Buffer, 5);
455 assert(SizeLen == 5);
456 Stream.pwrite((char *)Buffer, SizeLen, Offset);
457 }
458
459 // Write X as an signed LEB value at offset Offset in Stream, padded
460 // to allow patching.
461 static void
462 WritePatchableSLEB(raw_pwrite_stream &Stream, int32_t X, uint64_t Offset) {
463 uint8_t Buffer[5];
464 unsigned SizeLen = encodeSLEB128(X, Buffer, 5);
465 assert(SizeLen == 5);
466 Stream.pwrite((char *)Buffer, SizeLen, Offset);
467 }
468
469 // Write X as a plain integer value at offset Offset in Stream.
470 static void WriteI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) {
471 uint8_t Buffer[4];
472 support::endian::write32le(Buffer, X);
473 Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset);
474 }
475
476 static const MCSymbolWasm* ResolveSymbol(const MCSymbolWasm& Symbol) {
477 if (Symbol.isVariable()) {
478 const MCExpr *Expr = Symbol.getVariableValue();
479 auto *Inner = cast<MCSymbolRefExpr>(Expr);
480 return cast<MCSymbolWasm>(&Inner->getSymbol());
481 }
482 return &Symbol;
483 }
484
485 // Compute a value to write into the code at the location covered
486 // by RelEntry. This value isn't used by the static linker, since
487 // we have addends; it just serves to make the code more readable
488 // and to make standalone wasm modules directly usable.
489 uint32_t
490 WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry) {
491 const MCSymbolWasm *Sym = ResolveSymbol(*RelEntry.Symbol);
492
493 // For undefined symbols, use a hopefully invalid value.
494 if (!Sym->isDefined(/*SetUsed=*/false))
495 return UINT32_MAX;
496
497 uint32_t GlobalIndex = SymbolIndices[Sym];
498 const WasmGlobal& Global = Globals[GlobalIndex - NumGlobalImports];
499 uint64_t Address = Global.InitialValue + RelEntry.Addend;
500
501 // Ignore overflow. LLVM allows address arithmetic to silently wrap.
502 uint32_t Value = Address;
503
504 return Value;
505 }
506
507 static void addData(SmallVectorImpl<char> &DataBytes,
508 MCSectionWasm &DataSection) {
509 DEBUG(errs() << "addData: " << DataSection.getSectionName() << "\n");
510
511 DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
512
513 size_t LastFragmentSize = 0;
514 for (const MCFragment &Frag : DataSection) {
515 if (Frag.hasInstructions())
516 report_fatal_error("only data supported in data sections");
517
518 if (auto *Align = dyn_cast<MCAlignFragment>(&Frag)) {
519 if (Align->getValueSize() != 1)
520 report_fatal_error("only byte values supported for alignment");
521 // If nops are requested, use zeros, as this is the data section.
522 uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue();
523 uint64_t Size = std::min<uint64_t>(alignTo(DataBytes.size(),
524 Align->getAlignment()),
525 DataBytes.size() +
526 Align->getMaxBytesToEmit());
527 DataBytes.resize(Size, Value);
528 } else if (auto *Fill = dyn_cast<MCFillFragment>(&Frag)) {
529 DataBytes.insert(DataBytes.end(), Fill->getSize(), Fill->getValue());
530 } else {
531 const auto &DataFrag = cast<MCDataFragment>(Frag);
532 const SmallVectorImpl<char> &Contents = DataFrag.getContents();
533
534 DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
535 LastFragmentSize = Contents.size();
536 }
537 }
538
539 // Don't allow empty segments, or segments that end with zero-sized
540 // fragment, otherwise the linker cannot map symbols to a unique
541 // data segment. This can be triggered by zero-sized structs
542 // See: test/MC/WebAssembly/bss.ll
543 if (LastFragmentSize == 0)
544 DataBytes.resize(DataBytes.size() + 1);
545 DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n");
546 }
547
548 uint32_t WasmObjectWriter::getRelocationIndexValue(
549 const WasmRelocationEntry &RelEntry) {
550 switch (RelEntry.Type) {
551 case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
552 case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
553 if (!IndirectSymbolIndices.count(RelEntry.Symbol))
554 report_fatal_error("symbol not found table index space: " +
555 RelEntry.Symbol->getName());
556 return IndirectSymbolIndices[RelEntry.Symbol];
557 case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
558 case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB:
559 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB:
560 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
561 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
562 if (!SymbolIndices.count(RelEntry.Symbol))
563 report_fatal_error("symbol not found function/global index space: " +
564 RelEntry.Symbol->getName());
565 return SymbolIndices[RelEntry.Symbol];
566 case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
567 if (!TypeIndices.count(RelEntry.Symbol))
568 report_fatal_error("symbol not found in type index space: " +
569 RelEntry.Symbol->getName());
570 return TypeIndices[RelEntry.Symbol];
571 default:
572 llvm_unreachable("invalid relocation type");
573 }
574 }
575
576 // Apply the portions of the relocation records that we can handle ourselves
577 // directly.
578 void WasmObjectWriter::applyRelocations(
579 ArrayRef<WasmRelocationEntry> Relocations, uint64_t ContentsOffset) {
580 raw_pwrite_stream &Stream = getStream();
581 for (const WasmRelocationEntry &RelEntry : Relocations) {
582 uint64_t Offset = ContentsOffset +
583 RelEntry.FixupSection->getSectionOffset() +
584 RelEntry.Offset;
585
586 DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n");
587 switch (RelEntry.Type) {
588 case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
589 case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
590 case wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB:
591 case wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB: {
592 uint32_t Index = getRelocationIndexValue(RelEntry);
593 WritePatchableSLEB(Stream, Index, Offset);
594 break;
595 }
596 case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32: {
597 uint32_t Index = getRelocationIndexValue(RelEntry);
598 WriteI32(Stream, Index, Offset);
599 break;
600 }
601 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB: {
602 uint32_t Value = getProvisionalValue(RelEntry);
603 WritePatchableSLEB(Stream, Value, Offset);
604 break;
605 }
606 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB: {
607 uint32_t Value = getProvisionalValue(RelEntry);
608 WritePatchableLEB(Stream, Value, Offset);
609 break;
610 }
611 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32: {
612 uint32_t Value = getProvisionalValue(RelEntry);
613 WriteI32(Stream, Value, Offset);
614 break;
615 }
616 default:
617 llvm_unreachable("invalid relocation type");
618 }
619 }
620 }
621
622 // Write out the portions of the relocation records that the linker will
623 // need to handle.
624 void WasmObjectWriter::writeRelocations(
625 ArrayRef<WasmRelocationEntry> Relocations) {
626 raw_pwrite_stream &Stream = getStream();
627 for (const WasmRelocationEntry& RelEntry : Relocations) {
628
629 uint64_t Offset = RelEntry.Offset +
630 RelEntry.FixupSection->getSectionOffset();
631 uint32_t Index = getRelocationIndexValue(RelEntry);
632
633 encodeULEB128(RelEntry.Type, Stream);
634 encodeULEB128(Offset, Stream);
635 encodeULEB128(Index, Stream);
636 if (RelEntry.hasAddend())
637 encodeSLEB128(RelEntry.Addend, Stream);
638 }
639 }
640
641 void WasmObjectWriter::writeTypeSection(
642 ArrayRef<WasmFunctionType> FunctionTypes) {
643 if (FunctionTypes.empty())
644 return;
645
646 SectionBookkeeping Section;
647 startSection(Section, wasm::WASM_SEC_TYPE);
648
649 encodeULEB128(FunctionTypes.size(), getStream());
650
651 for (const WasmFunctionType &FuncTy : FunctionTypes) {
652 encodeSLEB128(wasm::WASM_TYPE_FUNC, getStream());
653 encodeULEB128(FuncTy.Params.size(), getStream());
654 for (wasm::ValType Ty : FuncTy.Params)
655 writeValueType(Ty);
656 encodeULEB128(FuncTy.Returns.size(), getStream());
657 for (wasm::ValType Ty : FuncTy.Returns)
658 writeValueType(Ty);
659 }
660
661 endSection(Section);
662 }
663
664 void WasmObjectWriter::writeImportSection(ArrayRef<WasmImport> Imports) {
665 if (Imports.empty())
666 return;
667
668 SectionBookkeeping Section;
669 startSection(Section, wasm::WASM_SEC_IMPORT);
670
671 encodeULEB128(Imports.size(), getStream());
672 for (const WasmImport &Import : Imports) {
673 writeString(Import.ModuleName);
674 writeString(Import.FieldName);
675
676 encodeULEB128(Import.Kind, getStream());
677
678 switch (Import.Kind) {
679 case wasm::WASM_EXTERNAL_FUNCTION:
680 encodeULEB128(Import.Type, getStream());
681 break;
682 case wasm::WASM_EXTERNAL_GLOBAL:
683 encodeSLEB128(int32_t(Import.Type), getStream());
684 encodeULEB128(0, getStream()); // mutability
685 break;
686 default:
687 llvm_unreachable("unsupported import kind");
688 }
689 }
690
691 endSection(Section);
692 }
693
694 void WasmObjectWriter::writeFunctionSection(ArrayRef<WasmFunction> Functions) {
695 if (Functions.empty())
696 return;
697
698 SectionBookkeeping Section;
699 startSection(Section, wasm::WASM_SEC_FUNCTION);
700
701 encodeULEB128(Functions.size(), getStream());
702 for (const WasmFunction &Func : Functions)
703 encodeULEB128(Func.Type, getStream());
704
705 endSection(Section);
706 }
707
708 void WasmObjectWriter::writeTableSection(uint32_t NumElements) {
709 // For now, always emit the table section, since indirect calls are not
710 // valid without it. In the future, we could perhaps be more clever and omit
711 // it if there are no indirect calls.
712
713 SectionBookkeeping Section;
714 startSection(Section, wasm::WASM_SEC_TABLE);
715
716 encodeULEB128(1, getStream()); // The number of tables.
717 // Fixed to 1 for now.
718 encodeSLEB128(wasm::WASM_TYPE_ANYFUNC, getStream()); // Type of table
719 encodeULEB128(0, getStream()); // flags
720 encodeULEB128(NumElements, getStream()); // initial
721
722 endSection(Section);
723 }
724
725 void WasmObjectWriter::writeMemorySection(uint32_t DataSize) {
726 // For now, always emit the memory section, since loads and stores are not
727 // valid without it. In the future, we could perhaps be more clever and omit
728 // it if there are no loads or stores.
729 SectionBookkeeping Section;
730 uint32_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
731
732 startSection(Section, wasm::WASM_SEC_MEMORY);
733 encodeULEB128(1, getStream()); // number of memory spaces
734
735 encodeULEB128(0, getStream()); // flags
736 encodeULEB128(NumPages, getStream()); // initial
737
738 endSection(Section);
739 }
740
741 void WasmObjectWriter::writeGlobalSection() {
742 if (Globals.empty())
743 return;
744
745 SectionBookkeeping Section;
746 startSection(Section, wasm::WASM_SEC_GLOBAL);
747
748 encodeULEB128(Globals.size(), getStream());
749 for (const WasmGlobal &Global : Globals) {
750 writeValueType(Global.Type);
751 write8(Global.IsMutable);
752
753 if (Global.HasImport) {
754 assert(Global.InitialValue == 0);
755 write8(wasm::WASM_OPCODE_GET_GLOBAL);
756 encodeULEB128(Global.ImportIndex, getStream());
757 } else {
758 assert(Global.ImportIndex == 0);
759 write8(wasm::WASM_OPCODE_I32_CONST);
760 encodeSLEB128(Global.InitialValue, getStream()); // offset
761 }
762 write8(wasm::WASM_OPCODE_END);
763 }
764
765 endSection(Section);
766 }
767
768 void WasmObjectWriter::writeExportSection(ArrayRef<WasmExport> Exports) {
769 if (Exports.empty())
770 return;
771
772 SectionBookkeeping Section;
773 startSection(Section, wasm::WASM_SEC_EXPORT);
774
775 encodeULEB128(Exports.size(), getStream());
776 for (const WasmExport &Export : Exports) {
777 writeString(Export.FieldName);
778 encodeSLEB128(Export.Kind, getStream());
779 encodeULEB128(Export.Index, getStream());
780 }
781
782 endSection(Section);
783 }
784
785 void WasmObjectWriter::writeElemSection(ArrayRef<uint32_t> TableElems) {
786 if (TableElems.empty())
787 return;
788
789 SectionBookkeeping Section;
790 startSection(Section, wasm::WASM_SEC_ELEM);
791
792 encodeULEB128(1, getStream()); // number of "segments"
793 encodeULEB128(0, getStream()); // the table index
794
795 // init expr for starting offset
796 write8(wasm::WASM_OPCODE_I32_CONST);
797 encodeSLEB128(0, getStream());
798 write8(wasm::WASM_OPCODE_END);
799
800 encodeULEB128(TableElems.size(), getStream());
801 for (uint32_t Elem : TableElems)
802 encodeULEB128(Elem, getStream());
803
804 endSection(Section);
805 }
806
807 void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
808 const MCAsmLayout &Layout,
809 ArrayRef<WasmFunction> Functions) {
810 if (Functions.empty())
811 return;
812
813 SectionBookkeeping Section;
814 startSection(Section, wasm::WASM_SEC_CODE);
815
816 encodeULEB128(Functions.size(), getStream());
817
818 for (const WasmFunction &Func : Functions) {
819 auto &FuncSection = static_cast<MCSectionWasm &>(Func.Sym->getSection());
820
821 int64_t Size = 0;
822 if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout))
823 report_fatal_error(".size expression must be evaluatable");
824
825 encodeULEB128(Size, getStream());
826 FuncSection.setSectionOffset(getStream().tell() - Section.ContentsOffset);
827 Asm.writeSectionData(&FuncSection, Layout);
828 }
829
830 // Apply fixups.
831 applyRelocations(CodeRelocations, Section.ContentsOffset);
832
833 endSection(Section);
834 }
835
836 void WasmObjectWriter::writeDataSection(ArrayRef<WasmDataSegment> Segments) {
837 if (Segments.empty())
838 return;
839
840 SectionBookkeeping Section;
841 startSection(Section, wasm::WASM_SEC_DATA);
842
843 encodeULEB128(Segments.size(), getStream()); // count
844
845 for (const WasmDataSegment & Segment : Segments) {
846 encodeULEB128(0, getStream()); // memory index
847 write8(wasm::WASM_OPCODE_I32_CONST);
848 encodeSLEB128(Segment.Offset, getStream()); // offset
849 write8(wasm::WASM_OPCODE_END);
850 encodeULEB128(Segment.Data.size(), getStream()); // size
851 Segment.Section->setSectionOffset(getStream().tell() - Section.ContentsOffset);
852 writeBytes(Segment.Data); // data
853 }
854
855 // Apply fixups.
856 applyRelocations(DataRelocations, Section.ContentsOffset);
857
858 endSection(Section);
859 }
860
861 void WasmObjectWriter::writeNameSection(
862 ArrayRef<WasmFunction> Functions,
863 ArrayRef<WasmImport> Imports,
864 unsigned NumFuncImports) {
865 uint32_t TotalFunctions = NumFuncImports + Functions.size();
866 if (TotalFunctions == 0)
867 return;
868
869 SectionBookkeeping Section;
870 startSection(Section, wasm::WASM_SEC_CUSTOM, "name");
871 SectionBookkeeping SubSection;
872 startSection(SubSection, wasm::WASM_NAMES_FUNCTION);
873
874 encodeULEB128(TotalFunctions, getStream());
875 uint32_t Index = 0;
876 for (const WasmImport &Import : Imports) {
877 if (Import.Kind == wasm::WASM_EXTERNAL_FUNCTION) {
878 encodeULEB128(Index, getStream());
879 writeString(Import.FieldName);
880 ++Index;
881 }
882 }
883 for (const WasmFunction &Func : Functions) {
884 encodeULEB128(Index, getStream());
885 writeString(Func.Sym->getName());
886 ++Index;
887 }
888
889 endSection(SubSection);
890 endSection(Section);
891 }
892
893 void WasmObjectWriter::writeCodeRelocSection() {
894 // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
895 // for descriptions of the reloc sections.
896
897 if (CodeRelocations.empty())
898 return;
899
900 SectionBookkeeping Section;
901 startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.CODE");
902
903 encodeULEB128(wasm::WASM_SEC_CODE, getStream());
904 encodeULEB128(CodeRelocations.size(), getStream());
905
906 writeRelocations(CodeRelocations);
907
908 endSection(Section);
909 }
910
911 void WasmObjectWriter::writeDataRelocSection() {
912 // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
913 // for descriptions of the reloc sections.
914
915 if (DataRelocations.empty())
916 return;
917
918 SectionBookkeeping Section;
919 startSection(Section, wasm::WASM_SEC_CUSTOM, "reloc.DATA");
920
921 encodeULEB128(wasm::WASM_SEC_DATA, getStream());
922 encodeULEB128(DataRelocations.size(), getStream());
923
924 writeRelocations(DataRelocations);
925
926 endSection(Section);
927 }
928
929 void WasmObjectWriter::writeLinkingMetaDataSection(
930 ArrayRef<WasmDataSegment> Segments, uint32_t DataSize,
931 SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags,
932 bool HasStackPointer, uint32_t StackPointerGlobal) {
933 SectionBookkeeping Section;
934 startSection(Section, wasm::WASM_SEC_CUSTOM, "linking");
935 SectionBookkeeping SubSection;
936
937 if (HasStackPointer) {
938 startSection(SubSection, wasm::WASM_STACK_POINTER);
939 encodeULEB128(StackPointerGlobal, getStream()); // id
940 endSection(SubSection);
941 }
942
943 if (SymbolFlags.size() != 0) {
944 startSection(SubSection, wasm::WASM_SYMBOL_INFO);
945 encodeULEB128(SymbolFlags.size(), getStream());
946 for (auto Pair: SymbolFlags) {
947 writeString(Pair.first);
948 encodeULEB128(Pair.second, getStream());
949 }
950 endSection(SubSection);
951 }
952
953 if (DataSize > 0) {
954 startSection(SubSection, wasm::WASM_DATA_SIZE);
955 encodeULEB128(DataSize, getStream());
956 endSection(SubSection);
957 }
958
959 if (Segments.size()) {
960 startSection(SubSection, wasm::WASM_SEGMENT_INFO);
961 encodeULEB128(Segments.size(), getStream());
962 for (const WasmDataSegment &Segment : Segments) {
963 writeString(Segment.Name);
964 encodeULEB128(Segment.Alignment, getStream());
965 encodeULEB128(Segment.Flags, getStream());
966 }
967 endSection(SubSection);
968 }
969
970 endSection(Section);
971 }
972
973 uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm& Symbol) {
974 assert(Symbol.isFunction());
975 assert(TypeIndices.count(&Symbol));
976 return TypeIndices[&Symbol];
977 }
978
979 uint32_t WasmObjectWriter::registerFunctionType(const MCSymbolWasm& Symbol) {
980 assert(Symbol.isFunction());
981
982 WasmFunctionType F;
983 const MCSymbolWasm* ResolvedSym = ResolveSymbol(Symbol);
984 F.Returns = ResolvedSym->getReturns();
985 F.Params = ResolvedSym->getParams();
986
987 auto Pair =
988 FunctionTypeIndices.insert(std::make_pair(F, FunctionTypes.size()));
989 if (Pair.second)
990 FunctionTypes.push_back(F);
991 TypeIndices[&Symbol] = Pair.first->second;
992
993 DEBUG(dbgs() << "registerFunctionType: " << Symbol << " new:" << Pair.second << "\n");
994 DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n");
995 return Pair.first->second;
996 }
997
998 void WasmObjectWriter::writeObject(MCAssembler &Asm,
999 const MCAsmLayout &Layout) {
1000 DEBUG(dbgs() << "WasmObjectWriter::writeObject\n");
1001 MCContext &Ctx = Asm.getContext();
1002 wasm::ValType PtrType = is64Bit() ? wasm::ValType::I64 : wasm::ValType::I32;
1003
1004 // Collect information from the available symbols.
1005 SmallVector<WasmFunction, 4> Functions;
1006 SmallVector<uint32_t, 4> TableElems;
1007 SmallVector<WasmImport, 4> Imports;
1008 SmallVector<WasmExport, 4> Exports;
1009 SmallVector<std::pair<StringRef, uint32_t>, 4> SymbolFlags;
1010 SmallPtrSet<const MCSymbolWasm *, 4> IsAddressTaken;
1011 unsigned NumFuncImports = 0;
1012 SmallVector<WasmDataSegment, 4> DataSegments;
1013 uint32_t StackPointerGlobal = 0;
1014 uint32_t DataSize = 0;
1015 bool HasStackPointer = false;
1016
1017 // Populate the IsAddressTaken set.
1018 for (const WasmRelocationEntry &RelEntry : CodeRelocations) {
1019 switch (RelEntry.Type) {
1020 case wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB:
1021 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
1022 IsAddressTaken.insert(RelEntry.Symbol);
1023 break;
1024 default:
1025 break;
1026 }
1027 }
1028 for (const WasmRelocationEntry &RelEntry : DataRelocations) {
1029 switch (RelEntry.Type) {
1030 case wasm::R_WEBASSEMBLY_TABLE_INDEX_I32:
1031 case wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32:
1032 IsAddressTaken.insert(RelEntry.Symbol);
1033 break;
1034 default:
1035 break;
1036 }
1037 }
1038
1039 // Populate FunctionTypeIndices and Imports.
1040 for (const MCSymbol &S : Asm.symbols()) {
1041 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1042
1043 if (WS.isTemporary())
1044 continue;
1045
1046 if (WS.isFunction())
1047 registerFunctionType(WS);
1048
1049 // If the symbol is not defined in this translation unit, import it.
1050 if (!WS.isDefined(/*SetUsed=*/false)) {
1051 WasmImport Import;
1052 Import.ModuleName = WS.getModuleName();
1053 Import.FieldName = WS.getName();
1054
1055 if (WS.isFunction()) {
1056 Import.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1057 Import.Type = getFunctionType(WS);
1058 SymbolIndices[&WS] = NumFuncImports;
1059 ++NumFuncImports;
1060 } else {
1061 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1062 Import.Type = int32_t(PtrType);
1063 SymbolIndices[&WS] = NumGlobalImports;
1064 ++NumGlobalImports;
1065 }
1066
1067 Imports.push_back(Import);
1068 }
1069 }
1070
1071 // In the special .global_variables section, we've encoded global
1072 // variables used by the function. Translate them into the Globals
1073 // list.
1074 MCSectionWasm *GlobalVars =
1075 Ctx.getWasmSection(".global_variables", SectionKind::getMetadata());
1076 if (!GlobalVars->getFragmentList().empty()) {
1077 if (GlobalVars->getFragmentList().size() != 1)
1078 report_fatal_error("only one .global_variables fragment supported");
1079 const MCFragment &Frag = *GlobalVars->begin();
1080 if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1081 report_fatal_error("only data supported in .global_variables");
1082 const auto &DataFrag = cast<MCDataFragment>(Frag);
1083 if (!DataFrag.getFixups().empty())
1084 report_fatal_error("fixups not supported in .global_variables");
1085 const SmallVectorImpl<char> &Contents = DataFrag.getContents();
1086 for (const uint8_t *p = (const uint8_t *)Contents.data(),
1087 *end = (const uint8_t *)Contents.data() + Contents.size();
1088 p != end; ) {
1089 WasmGlobal G;
1090 if (end - p < 3)
1091 report_fatal_error("truncated global variable encoding");
1092 G.Type = wasm::ValType(int8_t(*p++));
1093 G.IsMutable = bool(*p++);
1094 G.HasImport = bool(*p++);
1095 if (G.HasImport) {
1096 G.InitialValue = 0;
1097
1098 WasmImport Import;
1099 Import.ModuleName = (const char *)p;
1100 const uint8_t *nul = (const uint8_t *)memchr(p, '\0', end - p);
1101 if (!nul)
1102 report_fatal_error("global module name must be nul-terminated");
1103 p = nul + 1;
1104 nul = (const uint8_t *)memchr(p, '\0', end - p);
1105 if (!nul)
1106 report_fatal_error("global base name must be nul-terminated");
1107 Import.FieldName = (const char *)p;
1108 p = nul + 1;
1109
1110 Import.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1111 Import.Type = int32_t(G.Type);
1112
1113 G.ImportIndex = NumGlobalImports;
1114 ++NumGlobalImports;
1115
1116 Imports.push_back(Import);
1117 } else {
1118 unsigned n;
1119 G.InitialValue = decodeSLEB128(p, &n);
1120 G.ImportIndex = 0;
1121 if ((ptrdiff_t)n > end - p)
1122 report_fatal_error("global initial value must be valid SLEB128");
1123 p += n;
1124 }
1125 Globals.push_back(G);
1126 }
1127 }
1128
1129 // In the special .stack_pointer section, we've encoded the stack pointer
1130 // index.
1131 MCSectionWasm *StackPtr =
1132 Ctx.getWasmSection(".stack_pointer", SectionKind::getMetadata());
1133 if (!StackPtr->getFragmentList().empty()) {
1134 if (StackPtr->getFragmentList().size() != 1)
1135 report_fatal_error("only one .stack_pointer fragment supported");
1136 const MCFragment &Frag = *StackPtr->begin();
1137 if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data)
1138 report_fatal_error("only data supported in .stack_pointer");
1139 const auto &DataFrag = cast<MCDataFragment>(Frag);
1140 if (!DataFrag.getFixups().empty())
1141 report_fatal_error("fixups not supported in .stack_pointer");
1142 const SmallVectorImpl<char> &Contents = DataFrag.getContents();
1143 if (Contents.size() != 4)
1144 report_fatal_error("only one entry supported in .stack_pointer");
1145 HasStackPointer = true;
1146 StackPointerGlobal = NumGlobalImports + *(const int32_t *)Contents.data();
1147 }
1148
1149 for (MCSection &Sec : Asm) {
1150 auto &Section = static_cast<MCSectionWasm &>(Sec);
1151 if (!Section.isWasmData())
1152 continue;
1153
1154 DataSize = alignTo(DataSize, Section.getAlignment());
1155 DataSegments.emplace_back();
1156 WasmDataSegment &Segment = DataSegments.back();
1157 Segment.Name = Section.getSectionName();
1158 Segment.Offset = DataSize;
1159 Segment.Section = &Section;
1160 addData(Segment.Data, Section);
1161 Segment.Alignment = Section.getAlignment();
1162 Segment.Flags = 0;
1163 DataSize += Segment.Data.size();
1164 Section.setMemoryOffset(Segment.Offset);
1165 }
1166
1167 // Handle regular defined and undefined symbols.
1168 for (const MCSymbol &S : Asm.symbols()) {
1169 // Ignore unnamed temporary symbols, which aren't ever exported, imported,
1170 // or used in relocations.
1171 if (S.isTemporary() && S.getName().empty())
1172 continue;
1173
1174 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1175 DEBUG(dbgs() << "MCSymbol: '" << S << "'"
1176 << " isDefined=" << S.isDefined() << " isExternal="
1177 << S.isExternal() << " isTemporary=" << S.isTemporary()
1178 << " isFunction=" << WS.isFunction()
1179 << " isWeak=" << WS.isWeak()
1180 << " isVariable=" << WS.isVariable() << "\n");
1181
1182 if (WS.isWeak())
1183 SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_WEAK);
1184
1185 if (WS.isVariable())
1186 continue;
1187
1188 unsigned Index;
1189
1190 if (WS.isFunction()) {
1191 if (WS.isDefined(/*SetUsed=*/false)) {
1192 if (WS.getOffset() != 0)
1193 report_fatal_error(
1194 "function sections must contain one function each");
1195
1196 if (WS.getSize() == 0)
1197 report_fatal_error(
1198 "function symbols must have a size set with .size");
1199
1200 // A definition. Take the next available index.
1201 Index = NumFuncImports + Functions.size();
1202
1203 // Prepare the function.
1204 WasmFunction Func;
1205 Func.Type = getFunctionType(WS);
1206 Func.Sym = &WS;
1207 SymbolIndices[&WS] = Index;
1208 Functions.push_back(Func);
1209 } else {
1210 // An import; the index was assigned above.
1211 Index = SymbolIndices.find(&WS)->second;
1212 }
1213
1214 DEBUG(dbgs() << " -> function index: " << Index << "\n");
1215
1216 // If needed, prepare the function to be called indirectly.
1217 if (IsAddressTaken.count(&WS) != 0) {
1218 IndirectSymbolIndices[&WS] = TableElems.size();
1219 DEBUG(dbgs() << " -> adding to table: " << TableElems.size() << "\n");
1220 TableElems.push_back(Index);
1221 }
1222 } else {
1223 if (WS.isTemporary() && !WS.getSize())
1224 continue;
1225
1226 if (!WS.isDefined(/*SetUsed=*/false))
1227 continue;
1228
1229 if (!WS.getSize())
1230 report_fatal_error("data symbols must have a size set with .size: " +
1231 WS.getName());
1232
1233 int64_t Size = 0;
1234 if (!WS.getSize()->evaluateAsAbsolute(Size, Layout))
1235 report_fatal_error(".size expression must be evaluatable");
1236
1237 // For each global, prepare a corresponding wasm global holding its
1238 // address. For externals these will also be named exports.
1239 Index = NumGlobalImports + Globals.size();
1240 auto &DataSection = static_cast<MCSectionWasm &>(WS.getSection());
1241
1242 WasmGlobal Global;
1243 Global.Type = PtrType;
1244 Global.IsMutable = false;
1245 Global.HasImport = false;
1246 Global.InitialValue = DataSection.getMemoryOffset() + Layout.getSymbolOffset(WS);
1247 Global.ImportIndex = 0;
1248 SymbolIndices[&WS] = Index;
1249 DEBUG(dbgs() << " -> global index: " << Index << "\n");
1250 Globals.push_back(Global);
1251 }
1252
1253 // If the symbol is visible outside this translation unit, export it.
1254 if (WS.isDefined(/*SetUsed=*/false)) {
1255 WasmExport Export;
1256 Export.FieldName = WS.getName();
1257 Export.Index = Index;
1258 if (WS.isFunction())
1259 Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1260 else
1261 Export.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1262 DEBUG(dbgs() << " -> export " << Exports.size() << "\n");
1263 Exports.push_back(Export);
1264 if (!WS.isExternal())
1265 SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_LOCAL);
1266 }
1267 }
1268
1269 // Handle weak aliases. We need to process these in a separate pass because
1270 // we need to have processed the target of the alias before the alias itself
1271 // and the symbols are not necessarily ordered in this way.
1272 for (const MCSymbol &S : Asm.symbols()) {
1273 if (!S.isVariable())
1274 continue;
1275
1276 assert(S.isDefined(/*SetUsed=*/false));
1277
1278 // Find the target symbol of this weak alias and export that index
1279 const auto &WS = static_cast<const MCSymbolWasm &>(S);
1280 const MCSymbolWasm *ResolvedSym = ResolveSymbol(WS);
1281 DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym << "'\n");
1282 assert(SymbolIndices.count(ResolvedSym) > 0);
1283 uint32_t Index = SymbolIndices.find(ResolvedSym)->second;
1284 DEBUG(dbgs() << " -> index:" << Index << "\n");
1285
1286 SymbolIndices[&WS] = Index;
1287 WasmExport Export;
1288 Export.FieldName = WS.getName();
1289 Export.Index = Index;
1290 if (WS.isFunction())
1291 Export.Kind = wasm::WASM_EXTERNAL_FUNCTION;
1292 else
1293 Export.Kind = wasm::WASM_EXTERNAL_GLOBAL;
1294 DEBUG(dbgs() << " -> export " << Exports.size() << "\n");
1295 Exports.push_back(Export);
1296
1297 if (!WS.isExternal())
1298 SymbolFlags.emplace_back(WS.getName(), wasm::WASM_SYMBOL_BINDING_LOCAL);
1299 }
1300
1301 // Add types for indirect function calls.
1302 for (const WasmRelocationEntry &Fixup : CodeRelocations) {
1303 if (Fixup.Type != wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB)
1304 continue;
1305
1306 registerFunctionType(*Fixup.Symbol);
1307 }
1308
1309 // Write out the Wasm header.
1310 writeHeader(Asm);
1311
1312 writeTypeSection(FunctionTypes);
1313 writeImportSection(Imports);
1314 writeFunctionSection(Functions);
1315 writeTableSection(TableElems.size());
1316 writeMemorySection(DataSize);
1317 writeGlobalSection();
1318 writeExportSection(Exports);
1319 // TODO: Start Section
1320 writeElemSection(TableElems);
1321 writeCodeSection(Asm, Layout, Functions);
1322 writeDataSection(DataSegments);
1323 writeNameSection(Functions, Imports, NumFuncImports);
1324 writeCodeRelocSection();
1325 writeDataRelocSection();
1326 writeLinkingMetaDataSection(DataSegments, DataSize, SymbolFlags,
1327 HasStackPointer, StackPointerGlobal);
1328
1329 // TODO: Translate the .comment section to the output.
1330 // TODO: Translate debug sections to the output.
1331 }
1332
1333 std::unique_ptr<MCObjectWriter>
1334 llvm::createWasmObjectWriter(std::unique_ptr<MCWasmObjectTargetWriter> MOTW,
1335 raw_pwrite_stream &OS) {
1336 // FIXME: Can't use make_unique<WasmObjectWriter>(...) as WasmObjectWriter's
1337 // destructor is private. Is that necessary?
1338 return std::unique_ptr<MCObjectWriter>(
1339 new WasmObjectWriter(std::move(MOTW), OS));
1340 }