//===- lib/MC/WasmObjectWriter.cpp - Wasm File Writer ---------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// // // This file implements Wasm object file writer information. // //===----------------------------------------------------------------------===// #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/BinaryFormat/Wasm.h" #include "llvm/BinaryFormat/WasmTraits.h" #include "llvm/Config/llvm-config.h" #include "llvm/MC/MCAsmBackend.h" #include "llvm/MC/MCAsmLayout.h" #include "llvm/MC/MCAssembler.h" #include "llvm/MC/MCContext.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCFixupKindInfo.h" #include "llvm/MC/MCObjectWriter.h" #include "llvm/MC/MCSectionWasm.h" #include "llvm/MC/MCSymbolWasm.h" #include "llvm/MC/MCValue.h" #include "llvm/MC/MCWasmObjectWriter.h" #include "llvm/Support/Casting.h" #include "llvm/Support/Debug.h" #include "llvm/Support/EndianStream.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/LEB128.h" #include "llvm/Support/StringSaver.h" #include using namespace llvm; #define DEBUG_TYPE "mc" namespace { // When we create the indirect function table we start at 1, so that there is // and empty slot at 0 and therefore calling a null function pointer will trap. static const uint32_t InitialTableOffset = 1; // For patching purposes, we need to remember where each section starts, both // for patching up the section size field, and for patching up references to // locations within the section. struct SectionBookkeeping { // Where the size of the section is written. uint64_t SizeOffset; // Where the section header ends (without custom section name). uint64_t PayloadOffset; // Where the contents of the section starts. uint64_t ContentsOffset; uint32_t Index; }; // A wasm data segment. A wasm binary contains only a single data section // but that can contain many segments, each with their own virtual location // in memory. Each MCSection data created by llvm is modeled as its own // wasm data segment. struct WasmDataSegment { MCSectionWasm *Section; StringRef Name; uint32_t InitFlags; uint64_t Offset; uint32_t Alignment; uint32_t LinkingFlags; SmallVector Data; }; // A wasm function to be written into the function section. struct WasmFunction { uint32_t SigIndex; const MCSymbolWasm *Sym; }; // A wasm global to be written into the global section. struct WasmGlobal { wasm::WasmGlobalType Type; uint64_t InitialValue; }; // Information about a single item which is part of a COMDAT. For each data // segment or function which is in the COMDAT, there is a corresponding // WasmComdatEntry. struct WasmComdatEntry { unsigned Kind; uint32_t Index; }; // Information about a single relocation. struct WasmRelocationEntry { uint64_t Offset; // Where is the relocation. const MCSymbolWasm *Symbol; // The symbol to relocate with. int64_t Addend; // A value to add to the symbol. unsigned Type; // The type of the relocation. const MCSectionWasm *FixupSection; // The section the relocation is targeting. WasmRelocationEntry(uint64_t Offset, const MCSymbolWasm *Symbol, int64_t Addend, unsigned Type, const MCSectionWasm *FixupSection) : Offset(Offset), Symbol(Symbol), Addend(Addend), Type(Type), FixupSection(FixupSection) {} bool hasAddend() const { return wasm::relocTypeHasAddend(Type); } void print(raw_ostream &Out) const { Out << wasm::relocTypetoString(Type) << " Off=" << Offset << ", Sym=" << *Symbol << ", Addend=" << Addend << ", FixupSection=" << FixupSection->getName(); } #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) LLVM_DUMP_METHOD void dump() const { print(dbgs()); } #endif }; static const uint32_t InvalidIndex = -1; struct WasmCustomSection { StringRef Name; MCSectionWasm *Section; uint32_t OutputContentsOffset; uint32_t OutputIndex; WasmCustomSection(StringRef Name, MCSectionWasm *Section) : Name(Name), Section(Section), OutputContentsOffset(0), OutputIndex(InvalidIndex) {} }; #if !defined(NDEBUG) raw_ostream &operator<<(raw_ostream &OS, const WasmRelocationEntry &Rel) { Rel.print(OS); return OS; } #endif // Write X as an (unsigned) LEB value at offset Offset in Stream, padded // to allow patching. template void writePatchableLEB(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) { uint8_t Buffer[W]; unsigned SizeLen = encodeULEB128(X, Buffer, W); assert(SizeLen == W); Stream.pwrite((char *)Buffer, SizeLen, Offset); } // Write X as an signed LEB value at offset Offset in Stream, padded // to allow patching. template void writePatchableSLEB(raw_pwrite_stream &Stream, int64_t X, uint64_t Offset) { uint8_t Buffer[W]; unsigned SizeLen = encodeSLEB128(X, Buffer, W); assert(SizeLen == W); Stream.pwrite((char *)Buffer, SizeLen, Offset); } // Write X as a plain integer value at offset Offset in Stream. static void patchI32(raw_pwrite_stream &Stream, uint32_t X, uint64_t Offset) { uint8_t Buffer[4]; support::endian::write32le(Buffer, X); Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset); } static void patchI64(raw_pwrite_stream &Stream, uint64_t X, uint64_t Offset) { uint8_t Buffer[8]; support::endian::write64le(Buffer, X); Stream.pwrite((char *)Buffer, sizeof(Buffer), Offset); } bool isDwoSection(const MCSection &Sec) { return Sec.getName().endswith(".dwo"); } class WasmObjectWriter : public MCObjectWriter { support::endian::Writer *W; /// The target specific Wasm writer instance. std::unique_ptr TargetObjectWriter; // Relocations for fixing up references in the code section. std::vector CodeRelocations; // Relocations for fixing up references in the data section. std::vector DataRelocations; // Index values to use for fixing up call_indirect type indices. // Maps function symbols to the index of the type of the function DenseMap TypeIndices; // Maps function symbols to the table element index space. Used // for TABLE_INDEX relocation types (i.e. address taken functions). DenseMap TableIndices; // Maps function/global/table symbols to the // function/global/table/tag/section index space. DenseMap WasmIndices; DenseMap GOTIndices; // Maps data symbols to the Wasm segment and offset/size with the segment. DenseMap DataLocations; // Stores output data (index, relocations, content offset) for custom // section. std::vector CustomSections; std::unique_ptr ProducersSection; std::unique_ptr TargetFeaturesSection; // Relocations for fixing up references in the custom sections. DenseMap> CustomSectionsRelocations; // Map from section to defining function symbol. DenseMap SectionFunctions; DenseMap SignatureIndices; SmallVector Signatures; SmallVector DataSegments; unsigned NumFunctionImports = 0; unsigned NumGlobalImports = 0; unsigned NumTableImports = 0; unsigned NumTagImports = 0; uint32_t SectionCount = 0; enum class DwoMode { AllSections, NonDwoOnly, DwoOnly, }; bool IsSplitDwarf = false; raw_pwrite_stream *OS = nullptr; raw_pwrite_stream *DwoOS = nullptr; // TargetObjectWriter wranppers. bool is64Bit() const { return TargetObjectWriter->is64Bit(); } bool isEmscripten() const { return TargetObjectWriter->isEmscripten(); } void startSection(SectionBookkeeping &Section, unsigned SectionId); void startCustomSection(SectionBookkeeping &Section, StringRef Name); void endSection(SectionBookkeeping &Section); public: WasmObjectWriter(std::unique_ptr MOTW, raw_pwrite_stream &OS_) : TargetObjectWriter(std::move(MOTW)), OS(&OS_) {} WasmObjectWriter(std::unique_ptr MOTW, raw_pwrite_stream &OS_, raw_pwrite_stream &DwoOS_) : TargetObjectWriter(std::move(MOTW)), IsSplitDwarf(true), OS(&OS_), DwoOS(&DwoOS_) {} private: void reset() override { CodeRelocations.clear(); DataRelocations.clear(); TypeIndices.clear(); WasmIndices.clear(); GOTIndices.clear(); TableIndices.clear(); DataLocations.clear(); CustomSections.clear(); ProducersSection.reset(); TargetFeaturesSection.reset(); CustomSectionsRelocations.clear(); SignatureIndices.clear(); Signatures.clear(); DataSegments.clear(); SectionFunctions.clear(); NumFunctionImports = 0; NumGlobalImports = 0; NumTableImports = 0; MCObjectWriter::reset(); } void writeHeader(const MCAssembler &Asm); void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) override; void executePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) override; void prepareImports(SmallVectorImpl &Imports, MCAssembler &Asm, const MCAsmLayout &Layout); uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; uint64_t writeOneObject(MCAssembler &Asm, const MCAsmLayout &Layout, DwoMode Mode); void writeString(const StringRef Str) { encodeULEB128(Str.size(), W->OS); W->OS << Str; } void writeI32(int32_t val) { char Buffer[4]; support::endian::write32le(Buffer, val); W->OS.write(Buffer, sizeof(Buffer)); } void writeI64(int64_t val) { char Buffer[8]; support::endian::write64le(Buffer, val); W->OS.write(Buffer, sizeof(Buffer)); } void writeValueType(wasm::ValType Ty) { W->OS << static_cast(Ty); } void writeTypeSection(ArrayRef Signatures); void writeImportSection(ArrayRef Imports, uint64_t DataSize, uint32_t NumElements); void writeFunctionSection(ArrayRef Functions); void writeExportSection(ArrayRef Exports); void writeElemSection(const MCSymbolWasm *IndirectFunctionTable, ArrayRef TableElems); void writeDataCountSection(); uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout, ArrayRef Functions); uint32_t writeDataSection(const MCAsmLayout &Layout); void writeTagSection(ArrayRef Tags); void writeGlobalSection(ArrayRef Globals); void writeTableSection(ArrayRef Tables); void writeRelocSection(uint32_t SectionIndex, StringRef Name, std::vector &Relocations); void writeLinkingMetaDataSection( ArrayRef SymbolInfos, ArrayRef> InitFuncs, const std::map> &Comdats); void writeCustomSection(WasmCustomSection &CustomSection, const MCAssembler &Asm, const MCAsmLayout &Layout); void writeCustomRelocSections(); uint64_t getProvisionalValue(const WasmRelocationEntry &RelEntry, const MCAsmLayout &Layout); void applyRelocations(ArrayRef Relocations, uint64_t ContentsOffset, const MCAsmLayout &Layout); uint32_t getRelocationIndexValue(const WasmRelocationEntry &RelEntry); uint32_t getFunctionType(const MCSymbolWasm &Symbol); uint32_t getTagType(const MCSymbolWasm &Symbol); void registerFunctionType(const MCSymbolWasm &Symbol); void registerTagType(const MCSymbolWasm &Symbol); }; } // end anonymous namespace // Write out a section header and a patchable section size field. void WasmObjectWriter::startSection(SectionBookkeeping &Section, unsigned SectionId) { LLVM_DEBUG(dbgs() << "startSection " << SectionId << "\n"); W->OS << char(SectionId); Section.SizeOffset = W->OS.tell(); // The section size. We don't know the size yet, so reserve enough space // for any 32-bit value; we'll patch it later. encodeULEB128(0, W->OS, 5); // The position where the section starts, for measuring its size. Section.ContentsOffset = W->OS.tell(); Section.PayloadOffset = W->OS.tell(); Section.Index = SectionCount++; } void WasmObjectWriter::startCustomSection(SectionBookkeeping &Section, StringRef Name) { LLVM_DEBUG(dbgs() << "startCustomSection " << Name << "\n"); startSection(Section, wasm::WASM_SEC_CUSTOM); // The position where the section header ends, for measuring its size. Section.PayloadOffset = W->OS.tell(); // Custom sections in wasm also have a string identifier. writeString(Name); // The position where the custom section starts. Section.ContentsOffset = W->OS.tell(); } // Now that the section is complete and we know how big it is, patch up the // section size field at the start of the section. void WasmObjectWriter::endSection(SectionBookkeeping &Section) { uint64_t Size = W->OS.tell(); // /dev/null doesn't support seek/tell and can report offset of 0. // Simply skip this patching in that case. if (!Size) return; Size -= Section.PayloadOffset; if (uint32_t(Size) != Size) report_fatal_error("section size does not fit in a uint32_t"); LLVM_DEBUG(dbgs() << "endSection size=" << Size << "\n"); // Write the final section size to the payload_len field, which follows // the section id byte. writePatchableLEB<5>(static_cast(W->OS), Size, Section.SizeOffset); } // Emit the Wasm header. void WasmObjectWriter::writeHeader(const MCAssembler &Asm) { W->OS.write(wasm::WasmMagic, sizeof(wasm::WasmMagic)); W->write(wasm::WasmVersion); } void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) { // Some compilation units require the indirect function table to be present // but don't explicitly reference it. This is the case for call_indirect // without the reference-types feature, and also function bitcasts in all // cases. In those cases the __indirect_function_table has the // WASM_SYMBOL_NO_STRIP attribute. Here we make sure this symbol makes it to // the assembler, if needed. if (auto *Sym = Asm.getContext().lookupSymbol("__indirect_function_table")) { const auto *WasmSym = static_cast(Sym); if (WasmSym->isNoStrip()) Asm.registerSymbol(*Sym); } // Build a map of sections to the function that defines them, for use // in recordRelocation. for (const MCSymbol &S : Asm.symbols()) { const auto &WS = static_cast(S); if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) { const auto &Sec = static_cast(S.getSection()); auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S)); if (!Pair.second) report_fatal_error("section already has a defining function: " + Sec.getName()); } } } void WasmObjectWriter::recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) { // The WebAssembly backend should never generate FKF_IsPCRel fixups assert(!(Asm.getBackend().getFixupKindInfo(Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel)); const auto &FixupSection = cast(*Fragment->getParent()); uint64_t C = Target.getConstant(); uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); MCContext &Ctx = Asm.getContext(); bool IsLocRel = false; if (const MCSymbolRefExpr *RefB = Target.getSymB()) { const auto &SymB = cast(RefB->getSymbol()); if (FixupSection.getKind().isText()) { Ctx.reportError(Fixup.getLoc(), Twine("symbol '") + SymB.getName() + "' unsupported subtraction expression used in " "relocation in code section."); return; } if (SymB.isUndefined()) { Ctx.reportError(Fixup.getLoc(), Twine("symbol '") + SymB.getName() + "' can not be undefined in a subtraction expression"); return; } const MCSection &SecB = SymB.getSection(); if (&SecB != &FixupSection) { Ctx.reportError(Fixup.getLoc(), Twine("symbol '") + SymB.getName() + "' can not be placed in a different section"); return; } IsLocRel = true; C += FixupOffset - Layout.getSymbolOffset(SymB); } // We either rejected the fixup or folded B into C at this point. const MCSymbolRefExpr *RefA = Target.getSymA(); const auto *SymA = cast(&RefA->getSymbol()); // The .init_array isn't translated as data, so don't do relocations in it. if (FixupSection.getName().startswith(".init_array")) { SymA->setUsedInInitArray(); return; } if (SymA->isVariable()) { const MCExpr *Expr = SymA->getVariableValue(); if (const auto *Inner = dyn_cast(Expr)) if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) llvm_unreachable("weakref used in reloc not yet implemented"); } // Put any constant offset in an addend. Offsets can be negative, and // LLVM expects wrapping, in contrast to wasm's immediates which can't // be negative and don't wrap. FixedValue = 0; unsigned Type = TargetObjectWriter->getRelocType(Target, Fixup, IsLocRel); // Absolute offset within a section or a function. // Currently only supported for for metadata sections. // See: test/MC/WebAssembly/blockaddress.ll if (Type == wasm::R_WASM_FUNCTION_OFFSET_I32 || Type == wasm::R_WASM_FUNCTION_OFFSET_I64 || Type == wasm::R_WASM_SECTION_OFFSET_I32) { if (!FixupSection.getKind().isMetadata()) report_fatal_error("relocations for function or section offsets are " "only supported in metadata sections"); const MCSymbol *SectionSymbol = nullptr; const MCSection &SecA = SymA->getSection(); if (SecA.getKind().isText()) { auto SecSymIt = SectionFunctions.find(&SecA); if (SecSymIt == SectionFunctions.end()) report_fatal_error("section doesn\'t have defining symbol"); SectionSymbol = SecSymIt->second; } else { SectionSymbol = SecA.getBeginSymbol(); } if (!SectionSymbol) report_fatal_error("section symbol is required for relocation"); C += Layout.getSymbolOffset(*SymA); SymA = cast(SectionSymbol); } if (Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB || Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64 || Type == wasm::R_WASM_TABLE_INDEX_SLEB || Type == wasm::R_WASM_TABLE_INDEX_SLEB64 || Type == wasm::R_WASM_TABLE_INDEX_I32 || Type == wasm::R_WASM_TABLE_INDEX_I64) { // TABLE_INDEX relocs implicitly use the default indirect function table. // We require the function table to have already been defined. auto TableName = "__indirect_function_table"; MCSymbolWasm *Sym = cast_or_null(Ctx.lookupSymbol(TableName)); if (!Sym) { report_fatal_error("missing indirect function table symbol"); } else { if (!Sym->isFunctionTable()) report_fatal_error("__indirect_function_table symbol has wrong type"); // Ensure that __indirect_function_table reaches the output. Sym->setNoStrip(); Asm.registerSymbol(*Sym); } } // Relocation other than R_WASM_TYPE_INDEX_LEB are required to be // against a named symbol. if (Type != wasm::R_WASM_TYPE_INDEX_LEB) { if (SymA->getName().empty()) report_fatal_error("relocations against un-named temporaries are not yet " "supported by wasm"); SymA->setUsedInReloc(); } if (RefA->getKind() == MCSymbolRefExpr::VK_GOT) SymA->setUsedInGOT(); WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection); LLVM_DEBUG(dbgs() << "WasmReloc: " << Rec << "\n"); if (FixupSection.isWasmData()) { DataRelocations.push_back(Rec); } else if (FixupSection.getKind().isText()) { CodeRelocations.push_back(Rec); } else if (FixupSection.getKind().isMetadata()) { CustomSectionsRelocations[&FixupSection].push_back(Rec); } else { llvm_unreachable("unexpected section type"); } } // Compute a value to write into the code at the location covered // by RelEntry. This value isn't used by the static linker; it just serves // to make the object format more readable and more likely to be directly // useable. uint64_t WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry, const MCAsmLayout &Layout) { if ((RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_LEB || RelEntry.Type == wasm::R_WASM_GLOBAL_INDEX_I32) && !RelEntry.Symbol->isGlobal()) { assert(GOTIndices.count(RelEntry.Symbol) > 0 && "symbol not found in GOT index space"); return GOTIndices[RelEntry.Symbol]; } switch (RelEntry.Type) { case wasm::R_WASM_TABLE_INDEX_REL_SLEB: case wasm::R_WASM_TABLE_INDEX_REL_SLEB64: case wasm::R_WASM_TABLE_INDEX_SLEB: case wasm::R_WASM_TABLE_INDEX_SLEB64: case wasm::R_WASM_TABLE_INDEX_I32: case wasm::R_WASM_TABLE_INDEX_I64: { // Provisional value is table address of the resolved symbol itself const MCSymbolWasm *Base = cast(Layout.getBaseSymbol(*RelEntry.Symbol)); assert(Base->isFunction()); if (RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB || RelEntry.Type == wasm::R_WASM_TABLE_INDEX_REL_SLEB64) return TableIndices[Base] - InitialTableOffset; else return TableIndices[Base]; } case wasm::R_WASM_TYPE_INDEX_LEB: // Provisional value is same as the index return getRelocationIndexValue(RelEntry); case wasm::R_WASM_FUNCTION_INDEX_LEB: case wasm::R_WASM_GLOBAL_INDEX_LEB: case wasm::R_WASM_GLOBAL_INDEX_I32: case wasm::R_WASM_TAG_INDEX_LEB: case wasm::R_WASM_TABLE_NUMBER_LEB: // Provisional value is function/global/tag Wasm index assert(WasmIndices.count(RelEntry.Symbol) > 0 && "symbol not found in wasm index space"); return WasmIndices[RelEntry.Symbol]; case wasm::R_WASM_FUNCTION_OFFSET_I32: case wasm::R_WASM_FUNCTION_OFFSET_I64: case wasm::R_WASM_SECTION_OFFSET_I32: { const auto &Section = static_cast(RelEntry.Symbol->getSection()); return Section.getSectionOffset() + RelEntry.Addend; } case wasm::R_WASM_MEMORY_ADDR_LEB: case wasm::R_WASM_MEMORY_ADDR_LEB64: case wasm::R_WASM_MEMORY_ADDR_SLEB: case wasm::R_WASM_MEMORY_ADDR_SLEB64: case wasm::R_WASM_MEMORY_ADDR_REL_SLEB: case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64: case wasm::R_WASM_MEMORY_ADDR_I32: case wasm::R_WASM_MEMORY_ADDR_I64: case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: { // Provisional value is address of the global plus the offset // For undefined symbols, use zero if (!RelEntry.Symbol->isDefined()) return 0; const wasm::WasmDataReference &SymRef = DataLocations[RelEntry.Symbol]; const WasmDataSegment &Segment = DataSegments[SymRef.Segment]; // Ignore overflow. LLVM allows address arithmetic to silently wrap. return Segment.Offset + SymRef.Offset + RelEntry.Addend; } default: llvm_unreachable("invalid relocation type"); } } static void addData(SmallVectorImpl &DataBytes, MCSectionWasm &DataSection) { LLVM_DEBUG(errs() << "addData: " << DataSection.getName() << "\n"); DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment())); for (const MCFragment &Frag : DataSection) { if (Frag.hasInstructions()) report_fatal_error("only data supported in data sections"); if (auto *Align = dyn_cast(&Frag)) { if (Align->getValueSize() != 1) report_fatal_error("only byte values supported for alignment"); // If nops are requested, use zeros, as this is the data section. uint8_t Value = Align->hasEmitNops() ? 0 : Align->getValue(); uint64_t Size = std::min(alignTo(DataBytes.size(), Align->getAlignment()), DataBytes.size() + Align->getMaxBytesToEmit()); DataBytes.resize(Size, Value); } else if (auto *Fill = dyn_cast(&Frag)) { int64_t NumValues; if (!Fill->getNumValues().evaluateAsAbsolute(NumValues)) llvm_unreachable("The fill should be an assembler constant"); DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues, Fill->getValue()); } else if (auto *LEB = dyn_cast(&Frag)) { const SmallVectorImpl &Contents = LEB->getContents(); llvm::append_range(DataBytes, Contents); } else { const auto &DataFrag = cast(Frag); const SmallVectorImpl &Contents = DataFrag.getContents(); llvm::append_range(DataBytes, Contents); } } LLVM_DEBUG(dbgs() << "addData -> " << DataBytes.size() << "\n"); } uint32_t WasmObjectWriter::getRelocationIndexValue(const WasmRelocationEntry &RelEntry) { if (RelEntry.Type == wasm::R_WASM_TYPE_INDEX_LEB) { if (!TypeIndices.count(RelEntry.Symbol)) report_fatal_error("symbol not found in type index space: " + RelEntry.Symbol->getName()); return TypeIndices[RelEntry.Symbol]; } return RelEntry.Symbol->getIndex(); } // Apply the portions of the relocation records that we can handle ourselves // directly. void WasmObjectWriter::applyRelocations( ArrayRef Relocations, uint64_t ContentsOffset, const MCAsmLayout &Layout) { auto &Stream = static_cast(W->OS); for (const WasmRelocationEntry &RelEntry : Relocations) { uint64_t Offset = ContentsOffset + RelEntry.FixupSection->getSectionOffset() + RelEntry.Offset; LLVM_DEBUG(dbgs() << "applyRelocation: " << RelEntry << "\n"); auto Value = getProvisionalValue(RelEntry, Layout); switch (RelEntry.Type) { case wasm::R_WASM_FUNCTION_INDEX_LEB: case wasm::R_WASM_TYPE_INDEX_LEB: case wasm::R_WASM_GLOBAL_INDEX_LEB: case wasm::R_WASM_MEMORY_ADDR_LEB: case wasm::R_WASM_TAG_INDEX_LEB: case wasm::R_WASM_TABLE_NUMBER_LEB: writePatchableLEB<5>(Stream, Value, Offset); break; case wasm::R_WASM_MEMORY_ADDR_LEB64: writePatchableLEB<10>(Stream, Value, Offset); break; case wasm::R_WASM_TABLE_INDEX_I32: case wasm::R_WASM_MEMORY_ADDR_I32: case wasm::R_WASM_FUNCTION_OFFSET_I32: case wasm::R_WASM_SECTION_OFFSET_I32: case wasm::R_WASM_GLOBAL_INDEX_I32: case wasm::R_WASM_MEMORY_ADDR_LOCREL_I32: patchI32(Stream, Value, Offset); break; case wasm::R_WASM_TABLE_INDEX_I64: case wasm::R_WASM_MEMORY_ADDR_I64: case wasm::R_WASM_FUNCTION_OFFSET_I64: patchI64(Stream, Value, Offset); break; case wasm::R_WASM_TABLE_INDEX_SLEB: case wasm::R_WASM_TABLE_INDEX_REL_SLEB: case wasm::R_WASM_MEMORY_ADDR_SLEB: case wasm::R_WASM_MEMORY_ADDR_REL_SLEB: case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: writePatchableSLEB<5>(Stream, Value, Offset); break; case wasm::R_WASM_TABLE_INDEX_SLEB64: case wasm::R_WASM_TABLE_INDEX_REL_SLEB64: case wasm::R_WASM_MEMORY_ADDR_SLEB64: case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64: writePatchableSLEB<10>(Stream, Value, Offset); break; default: llvm_unreachable("invalid relocation type"); } } } void WasmObjectWriter::writeTypeSection( ArrayRef Signatures) { if (Signatures.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_TYPE); encodeULEB128(Signatures.size(), W->OS); for (const wasm::WasmSignature &Sig : Signatures) { W->OS << char(wasm::WASM_TYPE_FUNC); encodeULEB128(Sig.Params.size(), W->OS); for (wasm::ValType Ty : Sig.Params) writeValueType(Ty); encodeULEB128(Sig.Returns.size(), W->OS); for (wasm::ValType Ty : Sig.Returns) writeValueType(Ty); } endSection(Section); } void WasmObjectWriter::writeImportSection(ArrayRef Imports, uint64_t DataSize, uint32_t NumElements) { if (Imports.empty()) return; uint64_t NumPages = (DataSize + wasm::WasmPageSize - 1) / wasm::WasmPageSize; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_IMPORT); encodeULEB128(Imports.size(), W->OS); for (const wasm::WasmImport &Import : Imports) { writeString(Import.Module); writeString(Import.Field); W->OS << char(Import.Kind); switch (Import.Kind) { case wasm::WASM_EXTERNAL_FUNCTION: encodeULEB128(Import.SigIndex, W->OS); break; case wasm::WASM_EXTERNAL_GLOBAL: W->OS << char(Import.Global.Type); W->OS << char(Import.Global.Mutable ? 1 : 0); break; case wasm::WASM_EXTERNAL_MEMORY: encodeULEB128(Import.Memory.Flags, W->OS); encodeULEB128(NumPages, W->OS); // initial break; case wasm::WASM_EXTERNAL_TABLE: W->OS << char(Import.Table.ElemType); encodeULEB128(0, W->OS); // flags encodeULEB128(NumElements, W->OS); // initial break; case wasm::WASM_EXTERNAL_TAG: W->OS << char(Import.Tag.Attribute); encodeULEB128(Import.Tag.SigIndex, W->OS); break; default: llvm_unreachable("unsupported import kind"); } } endSection(Section); } void WasmObjectWriter::writeFunctionSection(ArrayRef Functions) { if (Functions.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_FUNCTION); encodeULEB128(Functions.size(), W->OS); for (const WasmFunction &Func : Functions) encodeULEB128(Func.SigIndex, W->OS); endSection(Section); } void WasmObjectWriter::writeTagSection(ArrayRef Tags) { if (Tags.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_TAG); encodeULEB128(Tags.size(), W->OS); for (const wasm::WasmTagType &Tag : Tags) { W->OS << char(Tag.Attribute); encodeULEB128(Tag.SigIndex, W->OS); } endSection(Section); } void WasmObjectWriter::writeGlobalSection(ArrayRef Globals) { if (Globals.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_GLOBAL); encodeULEB128(Globals.size(), W->OS); for (const wasm::WasmGlobal &Global : Globals) { encodeULEB128(Global.Type.Type, W->OS); W->OS << char(Global.Type.Mutable); W->OS << char(Global.InitExpr.Opcode); switch (Global.Type.Type) { case wasm::WASM_TYPE_I32: encodeSLEB128(0, W->OS); break; case wasm::WASM_TYPE_I64: encodeSLEB128(0, W->OS); break; case wasm::WASM_TYPE_F32: writeI32(0); break; case wasm::WASM_TYPE_F64: writeI64(0); break; case wasm::WASM_TYPE_EXTERNREF: writeValueType(wasm::ValType::EXTERNREF); break; default: llvm_unreachable("unexpected type"); } W->OS << char(wasm::WASM_OPCODE_END); } endSection(Section); } void WasmObjectWriter::writeTableSection(ArrayRef Tables) { if (Tables.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_TABLE); encodeULEB128(Tables.size(), W->OS); for (const wasm::WasmTable &Table : Tables) { encodeULEB128(Table.Type.ElemType, W->OS); encodeULEB128(Table.Type.Limits.Flags, W->OS); encodeULEB128(Table.Type.Limits.Minimum, W->OS); if (Table.Type.Limits.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX) encodeULEB128(Table.Type.Limits.Maximum, W->OS); } endSection(Section); } void WasmObjectWriter::writeExportSection(ArrayRef Exports) { if (Exports.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_EXPORT); encodeULEB128(Exports.size(), W->OS); for (const wasm::WasmExport &Export : Exports) { writeString(Export.Name); W->OS << char(Export.Kind); encodeULEB128(Export.Index, W->OS); } endSection(Section); } void WasmObjectWriter::writeElemSection( const MCSymbolWasm *IndirectFunctionTable, ArrayRef TableElems) { if (TableElems.empty()) return; assert(IndirectFunctionTable); SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_ELEM); encodeULEB128(1, W->OS); // number of "segments" assert(WasmIndices.count(IndirectFunctionTable)); uint32_t TableNumber = WasmIndices.find(IndirectFunctionTable)->second; uint32_t Flags = 0; if (TableNumber) Flags |= wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER; encodeULEB128(Flags, W->OS); if (Flags & wasm::WASM_ELEM_SEGMENT_HAS_TABLE_NUMBER) encodeULEB128(TableNumber, W->OS); // the table number // init expr for starting offset W->OS << char(wasm::WASM_OPCODE_I32_CONST); encodeSLEB128(InitialTableOffset, W->OS); W->OS << char(wasm::WASM_OPCODE_END); if (Flags & wasm::WASM_ELEM_SEGMENT_MASK_HAS_ELEM_KIND) { // We only write active function table initializers, for which the elem kind // is specified to be written as 0x00 and interpreted to mean "funcref". const uint8_t ElemKind = 0; W->OS << ElemKind; } encodeULEB128(TableElems.size(), W->OS); for (uint32_t Elem : TableElems) encodeULEB128(Elem, W->OS); endSection(Section); } void WasmObjectWriter::writeDataCountSection() { if (DataSegments.empty()) return; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_DATACOUNT); encodeULEB128(DataSegments.size(), W->OS); endSection(Section); } uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout, ArrayRef Functions) { if (Functions.empty()) return 0; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_CODE); encodeULEB128(Functions.size(), W->OS); for (const WasmFunction &Func : Functions) { auto &FuncSection = static_cast(Func.Sym->getSection()); int64_t Size = 0; if (!Func.Sym->getSize()->evaluateAsAbsolute(Size, Layout)) report_fatal_error(".size expression must be evaluatable"); encodeULEB128(Size, W->OS); FuncSection.setSectionOffset(W->OS.tell() - Section.ContentsOffset); Asm.writeSectionData(W->OS, &FuncSection, Layout); } // Apply fixups. applyRelocations(CodeRelocations, Section.ContentsOffset, Layout); endSection(Section); return Section.Index; } uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) { if (DataSegments.empty()) return 0; SectionBookkeeping Section; startSection(Section, wasm::WASM_SEC_DATA); encodeULEB128(DataSegments.size(), W->OS); // count for (const WasmDataSegment &Segment : DataSegments) { encodeULEB128(Segment.InitFlags, W->OS); // flags if (Segment.InitFlags & wasm::WASM_DATA_SEGMENT_HAS_MEMINDEX) encodeULEB128(0, W->OS); // memory index if ((Segment.InitFlags & wasm::WASM_DATA_SEGMENT_IS_PASSIVE) == 0) { W->OS << char(is64Bit() ? wasm::WASM_OPCODE_I64_CONST : wasm::WASM_OPCODE_I32_CONST); encodeSLEB128(Segment.Offset, W->OS); // offset W->OS << char(wasm::WASM_OPCODE_END); } encodeULEB128(Segment.Data.size(), W->OS); // size Segment.Section->setSectionOffset(W->OS.tell() - Section.ContentsOffset); W->OS << Segment.Data; // data } // Apply fixups. applyRelocations(DataRelocations, Section.ContentsOffset, Layout); endSection(Section); return Section.Index; } void WasmObjectWriter::writeRelocSection( uint32_t SectionIndex, StringRef Name, std::vector &Relocs) { // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md // for descriptions of the reloc sections. if (Relocs.empty()) return; // First, ensure the relocations are sorted in offset order. In general they // should already be sorted since `recordRelocation` is called in offset // order, but for the code section we combine many MC sections into single // wasm section, and this order is determined by the order of Asm.Symbols() // not the sections order. llvm::stable_sort( Relocs, [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) { return (A.Offset + A.FixupSection->getSectionOffset()) < (B.Offset + B.FixupSection->getSectionOffset()); }); SectionBookkeeping Section; startCustomSection(Section, std::string("reloc.") + Name.str()); encodeULEB128(SectionIndex, W->OS); encodeULEB128(Relocs.size(), W->OS); for (const WasmRelocationEntry &RelEntry : Relocs) { uint64_t Offset = RelEntry.Offset + RelEntry.FixupSection->getSectionOffset(); uint32_t Index = getRelocationIndexValue(RelEntry); W->OS << char(RelEntry.Type); encodeULEB128(Offset, W->OS); encodeULEB128(Index, W->OS); if (RelEntry.hasAddend()) encodeSLEB128(RelEntry.Addend, W->OS); } endSection(Section); } void WasmObjectWriter::writeCustomRelocSections() { for (const auto &Sec : CustomSections) { auto &Relocations = CustomSectionsRelocations[Sec.Section]; writeRelocSection(Sec.OutputIndex, Sec.Name, Relocations); } } void WasmObjectWriter::writeLinkingMetaDataSection( ArrayRef SymbolInfos, ArrayRef> InitFuncs, const std::map> &Comdats) { SectionBookkeeping Section; startCustomSection(Section, "linking"); encodeULEB128(wasm::WasmMetadataVersion, W->OS); SectionBookkeeping SubSection; if (SymbolInfos.size() != 0) { startSection(SubSection, wasm::WASM_SYMBOL_TABLE); encodeULEB128(SymbolInfos.size(), W->OS); for (const wasm::WasmSymbolInfo &Sym : SymbolInfos) { encodeULEB128(Sym.Kind, W->OS); encodeULEB128(Sym.Flags, W->OS); switch (Sym.Kind) { case wasm::WASM_SYMBOL_TYPE_FUNCTION: case wasm::WASM_SYMBOL_TYPE_GLOBAL: case wasm::WASM_SYMBOL_TYPE_TAG: case wasm::WASM_SYMBOL_TYPE_TABLE: encodeULEB128(Sym.ElementIndex, W->OS); if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0 || (Sym.Flags & wasm::WASM_SYMBOL_EXPLICIT_NAME) != 0) writeString(Sym.Name); break; case wasm::WASM_SYMBOL_TYPE_DATA: writeString(Sym.Name); if ((Sym.Flags & wasm::WASM_SYMBOL_UNDEFINED) == 0) { encodeULEB128(Sym.DataRef.Segment, W->OS); encodeULEB128(Sym.DataRef.Offset, W->OS); encodeULEB128(Sym.DataRef.Size, W->OS); } break; case wasm::WASM_SYMBOL_TYPE_SECTION: { const uint32_t SectionIndex = CustomSections[Sym.ElementIndex].OutputIndex; encodeULEB128(SectionIndex, W->OS); break; } default: llvm_unreachable("unexpected kind"); } } endSection(SubSection); } if (DataSegments.size()) { startSection(SubSection, wasm::WASM_SEGMENT_INFO); encodeULEB128(DataSegments.size(), W->OS); for (const WasmDataSegment &Segment : DataSegments) { writeString(Segment.Name); encodeULEB128(Segment.Alignment, W->OS); encodeULEB128(Segment.LinkingFlags, W->OS); } endSection(SubSection); } if (!InitFuncs.empty()) { startSection(SubSection, wasm::WASM_INIT_FUNCS); encodeULEB128(InitFuncs.size(), W->OS); for (auto &StartFunc : InitFuncs) { encodeULEB128(StartFunc.first, W->OS); // priority encodeULEB128(StartFunc.second, W->OS); // function index } endSection(SubSection); } if (Comdats.size()) { startSection(SubSection, wasm::WASM_COMDAT_INFO); encodeULEB128(Comdats.size(), W->OS); for (const auto &C : Comdats) { writeString(C.first); encodeULEB128(0, W->OS); // flags for future use encodeULEB128(C.second.size(), W->OS); for (const WasmComdatEntry &Entry : C.second) { encodeULEB128(Entry.Kind, W->OS); encodeULEB128(Entry.Index, W->OS); } } endSection(SubSection); } endSection(Section); } void WasmObjectWriter::writeCustomSection(WasmCustomSection &CustomSection, const MCAssembler &Asm, const MCAsmLayout &Layout) { SectionBookkeeping Section; auto *Sec = CustomSection.Section; startCustomSection(Section, CustomSection.Name); Sec->setSectionOffset(W->OS.tell() - Section.ContentsOffset); Asm.writeSectionData(W->OS, Sec, Layout); CustomSection.OutputContentsOffset = Section.ContentsOffset; CustomSection.OutputIndex = Section.Index; endSection(Section); // Apply fixups. auto &Relocations = CustomSectionsRelocations[CustomSection.Section]; applyRelocations(Relocations, CustomSection.OutputContentsOffset, Layout); } uint32_t WasmObjectWriter::getFunctionType(const MCSymbolWasm &Symbol) { assert(Symbol.isFunction()); assert(TypeIndices.count(&Symbol)); return TypeIndices[&Symbol]; } uint32_t WasmObjectWriter::getTagType(const MCSymbolWasm &Symbol) { assert(Symbol.isTag()); assert(TypeIndices.count(&Symbol)); return TypeIndices[&Symbol]; } void WasmObjectWriter::registerFunctionType(const MCSymbolWasm &Symbol) { assert(Symbol.isFunction()); wasm::WasmSignature S; if (auto *Sig = Symbol.getSignature()) { S.Returns = Sig->Returns; S.Params = Sig->Params; } auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size())); if (Pair.second) Signatures.push_back(S); TypeIndices[&Symbol] = Pair.first->second; LLVM_DEBUG(dbgs() << "registerFunctionType: " << Symbol << " new:" << Pair.second << "\n"); LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n"); } void WasmObjectWriter::registerTagType(const MCSymbolWasm &Symbol) { assert(Symbol.isTag()); // TODO Currently we don't generate imported exceptions, but if we do, we // should have a way of infering types of imported exceptions. wasm::WasmSignature S; if (auto *Sig = Symbol.getSignature()) { S.Returns = Sig->Returns; S.Params = Sig->Params; } auto Pair = SignatureIndices.insert(std::make_pair(S, Signatures.size())); if (Pair.second) Signatures.push_back(S); TypeIndices[&Symbol] = Pair.first->second; LLVM_DEBUG(dbgs() << "registerTagType: " << Symbol << " new:" << Pair.second << "\n"); LLVM_DEBUG(dbgs() << " -> type index: " << Pair.first->second << "\n"); } static bool isInSymtab(const MCSymbolWasm &Sym) { if (Sym.isUsedInReloc() || Sym.isUsedInInitArray()) return true; if (Sym.isComdat() && !Sym.isDefined()) return false; if (Sym.isTemporary()) return false; if (Sym.isSection()) return false; if (Sym.omitFromLinkingSection()) return false; return true; } void WasmObjectWriter::prepareImports( SmallVectorImpl &Imports, MCAssembler &Asm, const MCAsmLayout &Layout) { // For now, always emit the memory import, since loads and stores are not // valid without it. In the future, we could perhaps be more clever and omit // it if there are no loads or stores. wasm::WasmImport MemImport; MemImport.Module = "env"; MemImport.Field = "__linear_memory"; MemImport.Kind = wasm::WASM_EXTERNAL_MEMORY; MemImport.Memory.Flags = is64Bit() ? wasm::WASM_LIMITS_FLAG_IS_64 : wasm::WASM_LIMITS_FLAG_NONE; Imports.push_back(MemImport); // Populate SignatureIndices, and Imports and WasmIndices for undefined // symbols. This must be done before populating WasmIndices for defined // symbols. for (const MCSymbol &S : Asm.symbols()) { const auto &WS = static_cast(S); // Register types for all functions, including those with private linkage // (because wasm always needs a type signature). if (WS.isFunction()) { const auto *BS = Layout.getBaseSymbol(S); if (!BS) report_fatal_error(Twine(S.getName()) + ": absolute addressing not supported!"); registerFunctionType(*cast(BS)); } if (WS.isTag()) registerTagType(WS); if (WS.isTemporary()) continue; // If the symbol is not defined in this translation unit, import it. if (!WS.isDefined() && !WS.isComdat()) { if (WS.isFunction()) { wasm::WasmImport Import; Import.Module = WS.getImportModule(); Import.Field = WS.getImportName(); Import.Kind = wasm::WASM_EXTERNAL_FUNCTION; Import.SigIndex = getFunctionType(WS); Imports.push_back(Import); assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = NumFunctionImports++; } else if (WS.isGlobal()) { if (WS.isWeak()) report_fatal_error("undefined global symbol cannot be weak"); wasm::WasmImport Import; Import.Field = WS.getImportName(); Import.Kind = wasm::WASM_EXTERNAL_GLOBAL; Import.Module = WS.getImportModule(); Import.Global = WS.getGlobalType(); Imports.push_back(Import); assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = NumGlobalImports++; } else if (WS.isTag()) { if (WS.isWeak()) report_fatal_error("undefined tag symbol cannot be weak"); wasm::WasmImport Import; Import.Module = WS.getImportModule(); Import.Field = WS.getImportName(); Import.Kind = wasm::WASM_EXTERNAL_TAG; Import.Tag.Attribute = wasm::WASM_TAG_ATTRIBUTE_EXCEPTION; Import.Tag.SigIndex = getTagType(WS); Imports.push_back(Import); assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = NumTagImports++; } else if (WS.isTable()) { if (WS.isWeak()) report_fatal_error("undefined table symbol cannot be weak"); wasm::WasmImport Import; Import.Module = WS.getImportModule(); Import.Field = WS.getImportName(); Import.Kind = wasm::WASM_EXTERNAL_TABLE; Import.Table = WS.getTableType(); Imports.push_back(Import); assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = NumTableImports++; } } } // Add imports for GOT globals for (const MCSymbol &S : Asm.symbols()) { const auto &WS = static_cast(S); if (WS.isUsedInGOT()) { wasm::WasmImport Import; if (WS.isFunction()) Import.Module = "GOT.func"; else Import.Module = "GOT.mem"; Import.Field = WS.getName(); Import.Kind = wasm::WASM_EXTERNAL_GLOBAL; Import.Global = {wasm::WASM_TYPE_I32, true}; Imports.push_back(Import); assert(GOTIndices.count(&WS) == 0); GOTIndices[&WS] = NumGlobalImports++; } } } uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) { support::endian::Writer MainWriter(*OS, support::little); W = &MainWriter; if (IsSplitDwarf) { uint64_t TotalSize = writeOneObject(Asm, Layout, DwoMode::NonDwoOnly); assert(DwoOS); support::endian::Writer DwoWriter(*DwoOS, support::little); W = &DwoWriter; return TotalSize + writeOneObject(Asm, Layout, DwoMode::DwoOnly); } else { return writeOneObject(Asm, Layout, DwoMode::AllSections); } } uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm, const MCAsmLayout &Layout, DwoMode Mode) { uint64_t StartOffset = W->OS.tell(); SectionCount = 0; CustomSections.clear(); LLVM_DEBUG(dbgs() << "WasmObjectWriter::writeObject\n"); // Collect information from the available symbols. SmallVector Functions; SmallVector TableElems; SmallVector Imports; SmallVector Exports; SmallVector Tags; SmallVector Globals; SmallVector Tables; SmallVector SymbolInfos; SmallVector, 2> InitFuncs; std::map> Comdats; uint64_t DataSize = 0; if (Mode != DwoMode::DwoOnly) { prepareImports(Imports, Asm, Layout); } // Populate DataSegments and CustomSections, which must be done before // populating DataLocations. for (MCSection &Sec : Asm) { auto &Section = static_cast(Sec); StringRef SectionName = Section.getName(); if (Mode == DwoMode::NonDwoOnly && isDwoSection(Sec)) continue; if (Mode == DwoMode::DwoOnly && !isDwoSection(Sec)) continue; LLVM_DEBUG(dbgs() << "Processing Section " << SectionName << " group " << Section.getGroup() << "\n";); // .init_array sections are handled specially elsewhere. if (SectionName.startswith(".init_array")) continue; // Code is handled separately if (Section.getKind().isText()) continue; if (Section.isWasmData()) { uint32_t SegmentIndex = DataSegments.size(); DataSize = alignTo(DataSize, Section.getAlignment()); DataSegments.emplace_back(); WasmDataSegment &Segment = DataSegments.back(); Segment.Name = SectionName; Segment.InitFlags = Section.getPassive() ? (uint32_t)wasm::WASM_DATA_SEGMENT_IS_PASSIVE : 0; Segment.Offset = DataSize; Segment.Section = &Section; addData(Segment.Data, Section); Segment.Alignment = Log2_32(Section.getAlignment()); Segment.LinkingFlags = Section.getSegmentFlags(); DataSize += Segment.Data.size(); Section.setSegmentIndex(SegmentIndex); if (const MCSymbolWasm *C = Section.getGroup()) { Comdats[C->getName()].emplace_back( WasmComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex}); } } else { // Create custom sections assert(Sec.getKind().isMetadata()); StringRef Name = SectionName; // For user-defined custom sections, strip the prefix if (Name.startswith(".custom_section.")) Name = Name.substr(strlen(".custom_section.")); MCSymbol *Begin = Sec.getBeginSymbol(); if (Begin) { assert(WasmIndices.count(cast(Begin)) == 0); WasmIndices[cast(Begin)] = CustomSections.size(); } // Separate out the producers and target features sections if (Name == "producers") { ProducersSection = std::make_unique(Name, &Section); continue; } if (Name == "target_features") { TargetFeaturesSection = std::make_unique(Name, &Section); continue; } // Custom sections can also belong to COMDAT groups. In this case the // decriptor's "index" field is the section index (in the final object // file), but that is not known until after layout, so it must be fixed up // later if (const MCSymbolWasm *C = Section.getGroup()) { Comdats[C->getName()].emplace_back( WasmComdatEntry{wasm::WASM_COMDAT_SECTION, static_cast(CustomSections.size())}); } CustomSections.emplace_back(Name, &Section); } } if (Mode != DwoMode::DwoOnly) { // Populate WasmIndices and DataLocations for defined symbols. for (const MCSymbol &S : Asm.symbols()) { // Ignore unnamed temporary symbols, which aren't ever exported, imported, // or used in relocations. if (S.isTemporary() && S.getName().empty()) continue; const auto &WS = static_cast(S); LLVM_DEBUG(dbgs() << "MCSymbol: " << toString(WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA)) << " '" << S << "'" << " isDefined=" << S.isDefined() << " isExternal=" << S.isExternal() << " isTemporary=" << S.isTemporary() << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden() << " isVariable=" << WS.isVariable() << "\n"); if (WS.isVariable()) continue; if (WS.isComdat() && !WS.isDefined()) continue; if (WS.isFunction()) { unsigned Index; if (WS.isDefined()) { if (WS.getOffset() != 0) report_fatal_error( "function sections must contain one function each"); if (WS.getSize() == nullptr) report_fatal_error( "function symbols must have a size set with .size"); // A definition. Write out the function body. Index = NumFunctionImports + Functions.size(); WasmFunction Func; Func.SigIndex = getFunctionType(WS); Func.Sym = &WS; assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = Index; Functions.push_back(Func); auto &Section = static_cast(WS.getSection()); if (const MCSymbolWasm *C = Section.getGroup()) { Comdats[C->getName()].emplace_back( WasmComdatEntry{wasm::WASM_COMDAT_FUNCTION, Index}); } if (WS.hasExportName()) { wasm::WasmExport Export; Export.Name = WS.getExportName(); Export.Kind = wasm::WASM_EXTERNAL_FUNCTION; Export.Index = Index; Exports.push_back(Export); } } else { // An import; the index was assigned above. Index = WasmIndices.find(&WS)->second; } LLVM_DEBUG(dbgs() << " -> function index: " << Index << "\n"); } else if (WS.isData()) { if (!isInSymtab(WS)) continue; if (!WS.isDefined()) { LLVM_DEBUG(dbgs() << " -> segment index: -1" << "\n"); continue; } if (!WS.getSize()) report_fatal_error("data symbols must have a size set with .size: " + WS.getName()); int64_t Size = 0; if (!WS.getSize()->evaluateAsAbsolute(Size, Layout)) report_fatal_error(".size expression must be evaluatable"); auto &DataSection = static_cast(WS.getSection()); if (!DataSection.isWasmData()) report_fatal_error("data symbols must live in a data section: " + WS.getName()); // For each data symbol, export it in the symtab as a reference to the // corresponding Wasm data segment. wasm::WasmDataReference Ref = wasm::WasmDataReference{ DataSection.getSegmentIndex(), Layout.getSymbolOffset(WS), static_cast(Size)}; assert(DataLocations.count(&WS) == 0); DataLocations[&WS] = Ref; LLVM_DEBUG(dbgs() << " -> segment index: " << Ref.Segment << "\n"); } else if (WS.isGlobal()) { // A "true" Wasm global (currently just __stack_pointer) if (WS.isDefined()) { wasm::WasmGlobal Global; Global.Type = WS.getGlobalType(); Global.Index = NumGlobalImports + Globals.size(); switch (Global.Type.Type) { case wasm::WASM_TYPE_I32: Global.InitExpr.Opcode = wasm::WASM_OPCODE_I32_CONST; break; case wasm::WASM_TYPE_I64: Global.InitExpr.Opcode = wasm::WASM_OPCODE_I64_CONST; break; case wasm::WASM_TYPE_F32: Global.InitExpr.Opcode = wasm::WASM_OPCODE_F32_CONST; break; case wasm::WASM_TYPE_F64: Global.InitExpr.Opcode = wasm::WASM_OPCODE_F64_CONST; break; case wasm::WASM_TYPE_EXTERNREF: Global.InitExpr.Opcode = wasm::WASM_OPCODE_REF_NULL; break; default: llvm_unreachable("unexpected type"); } assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = Global.Index; Globals.push_back(Global); } else { // An import; the index was assigned above LLVM_DEBUG(dbgs() << " -> global index: " << WasmIndices.find(&WS)->second << "\n"); } } else if (WS.isTable()) { if (WS.isDefined()) { wasm::WasmTable Table; Table.Index = NumTableImports + Tables.size(); Table.Type = WS.getTableType(); assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = Table.Index; Tables.push_back(Table); } LLVM_DEBUG(dbgs() << " -> table index: " << WasmIndices.find(&WS)->second << "\n"); } else if (WS.isTag()) { // C++ exception symbol (__cpp_exception) unsigned Index; if (WS.isDefined()) { Index = NumTagImports + Tags.size(); wasm::WasmTagType Tag; Tag.SigIndex = getTagType(WS); Tag.Attribute = wasm::WASM_TAG_ATTRIBUTE_EXCEPTION; assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = Index; Tags.push_back(Tag); } else { // An import; the index was assigned above. assert(WasmIndices.count(&WS) > 0); } LLVM_DEBUG(dbgs() << " -> tag index: " << WasmIndices.find(&WS)->second << "\n"); } else { assert(WS.isSection()); } } // Populate WasmIndices and DataLocations for aliased symbols. We need to // process these in a separate pass because we need to have processed the // target of the alias before the alias itself and the symbols are not // necessarily ordered in this way. for (const MCSymbol &S : Asm.symbols()) { if (!S.isVariable()) continue; assert(S.isDefined()); const auto *BS = Layout.getBaseSymbol(S); if (!BS) report_fatal_error(Twine(S.getName()) + ": absolute addressing not supported!"); const MCSymbolWasm *Base = cast(BS); // Find the target symbol of this weak alias and export that index const auto &WS = static_cast(S); LLVM_DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *Base << "'\n"); if (Base->isFunction()) { assert(WasmIndices.count(Base) > 0); uint32_t WasmIndex = WasmIndices.find(Base)->second; assert(WasmIndices.count(&WS) == 0); WasmIndices[&WS] = WasmIndex; LLVM_DEBUG(dbgs() << " -> index:" << WasmIndex << "\n"); } else if (Base->isData()) { auto &DataSection = static_cast(WS.getSection()); uint64_t Offset = Layout.getSymbolOffset(S); int64_t Size = 0; // For data symbol alias we use the size of the base symbol as the // size of the alias. When an offset from the base is involved this // can result in a offset + size goes past the end of the data section // which out object format doesn't support. So we must clamp it. if (!Base->getSize()->evaluateAsAbsolute(Size, Layout)) report_fatal_error(".size expression must be evaluatable"); const WasmDataSegment &Segment = DataSegments[DataSection.getSegmentIndex()]; Size = std::min(static_cast(Size), Segment.Data.size() - Offset); wasm::WasmDataReference Ref = wasm::WasmDataReference{ DataSection.getSegmentIndex(), static_cast(Layout.getSymbolOffset(S)), static_cast(Size)}; DataLocations[&WS] = Ref; LLVM_DEBUG(dbgs() << " -> index:" << Ref.Segment << "\n"); } else { report_fatal_error("don't yet support global/tag aliases"); } } } // Finally, populate the symbol table itself, in its "natural" order. for (const MCSymbol &S : Asm.symbols()) { const auto &WS = static_cast(S); if (!isInSymtab(WS)) { WS.setIndex(InvalidIndex); continue; } LLVM_DEBUG(dbgs() << "adding to symtab: " << WS << "\n"); uint32_t Flags = 0; if (WS.isWeak()) Flags |= wasm::WASM_SYMBOL_BINDING_WEAK; if (WS.isHidden()) Flags |= wasm::WASM_SYMBOL_VISIBILITY_HIDDEN; if (!WS.isExternal() && WS.isDefined()) Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL; if (WS.isUndefined()) Flags |= wasm::WASM_SYMBOL_UNDEFINED; if (WS.isNoStrip()) { Flags |= wasm::WASM_SYMBOL_NO_STRIP; if (isEmscripten()) { Flags |= wasm::WASM_SYMBOL_EXPORTED; } } if (WS.hasImportName()) Flags |= wasm::WASM_SYMBOL_EXPLICIT_NAME; if (WS.hasExportName()) Flags |= wasm::WASM_SYMBOL_EXPORTED; wasm::WasmSymbolInfo Info; Info.Name = WS.getName(); Info.Kind = WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA); Info.Flags = Flags; if (!WS.isData()) { assert(WasmIndices.count(&WS) > 0); Info.ElementIndex = WasmIndices.find(&WS)->second; } else if (WS.isDefined()) { assert(DataLocations.count(&WS) > 0); Info.DataRef = DataLocations.find(&WS)->second; } WS.setIndex(SymbolInfos.size()); SymbolInfos.emplace_back(Info); } { auto HandleReloc = [&](const WasmRelocationEntry &Rel) { // Functions referenced by a relocation need to put in the table. This is // purely to make the object file's provisional values readable, and is // ignored by the linker, which re-calculates the relocations itself. if (Rel.Type != wasm::R_WASM_TABLE_INDEX_I32 && Rel.Type != wasm::R_WASM_TABLE_INDEX_I64 && Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB && Rel.Type != wasm::R_WASM_TABLE_INDEX_SLEB64 && Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB && Rel.Type != wasm::R_WASM_TABLE_INDEX_REL_SLEB64) return; assert(Rel.Symbol->isFunction()); const MCSymbolWasm *Base = cast(Layout.getBaseSymbol(*Rel.Symbol)); uint32_t FunctionIndex = WasmIndices.find(Base)->second; uint32_t TableIndex = TableElems.size() + InitialTableOffset; if (TableIndices.try_emplace(Base, TableIndex).second) { LLVM_DEBUG(dbgs() << " -> adding " << Base->getName() << " to table: " << TableIndex << "\n"); TableElems.push_back(FunctionIndex); registerFunctionType(*Base); } }; for (const WasmRelocationEntry &RelEntry : CodeRelocations) HandleReloc(RelEntry); for (const WasmRelocationEntry &RelEntry : DataRelocations) HandleReloc(RelEntry); } // Translate .init_array section contents into start functions. for (const MCSection &S : Asm) { const auto &WS = static_cast(S); if (WS.getName().startswith(".fini_array")) report_fatal_error(".fini_array sections are unsupported"); if (!WS.getName().startswith(".init_array")) continue; if (WS.getFragmentList().empty()) continue; // init_array is expected to contain a single non-empty data fragment if (WS.getFragmentList().size() != 3) report_fatal_error("only one .init_array section fragment supported"); auto IT = WS.begin(); const MCFragment &EmptyFrag = *IT; if (EmptyFrag.getKind() != MCFragment::FT_Data) report_fatal_error(".init_array section should be aligned"); IT = std::next(IT); const MCFragment &AlignFrag = *IT; if (AlignFrag.getKind() != MCFragment::FT_Align) report_fatal_error(".init_array section should be aligned"); if (cast(AlignFrag).getAlignment() != (is64Bit() ? 8 : 4)) report_fatal_error(".init_array section should be aligned for pointers"); const MCFragment &Frag = *std::next(IT); if (Frag.hasInstructions() || Frag.getKind() != MCFragment::FT_Data) report_fatal_error("only data supported in .init_array section"); uint16_t Priority = UINT16_MAX; unsigned PrefixLength = strlen(".init_array"); if (WS.getName().size() > PrefixLength) { if (WS.getName()[PrefixLength] != '.') report_fatal_error( ".init_array section priority should start with '.'"); if (WS.getName().substr(PrefixLength + 1).getAsInteger(10, Priority)) report_fatal_error("invalid .init_array section priority"); } const auto &DataFrag = cast(Frag); const SmallVectorImpl &Contents = DataFrag.getContents(); for (const uint8_t * P = (const uint8_t *)Contents.data(), *End = (const uint8_t *)Contents.data() + Contents.size(); P != End; ++P) { if (*P != 0) report_fatal_error("non-symbolic data in .init_array section"); } for (const MCFixup &Fixup : DataFrag.getFixups()) { assert(Fixup.getKind() == MCFixup::getKindForSize(is64Bit() ? 8 : 4, false)); const MCExpr *Expr = Fixup.getValue(); auto *SymRef = dyn_cast(Expr); if (!SymRef) report_fatal_error("fixups in .init_array should be symbol references"); const auto &TargetSym = cast(SymRef->getSymbol()); if (TargetSym.getIndex() == InvalidIndex) report_fatal_error("symbols in .init_array should exist in symtab"); if (!TargetSym.isFunction()) report_fatal_error("symbols in .init_array should be for functions"); InitFuncs.push_back( std::make_pair(Priority, TargetSym.getIndex())); } } // Write out the Wasm header. writeHeader(Asm); uint32_t CodeSectionIndex, DataSectionIndex; if (Mode != DwoMode::DwoOnly) { writeTypeSection(Signatures); writeImportSection(Imports, DataSize, TableElems.size()); writeFunctionSection(Functions); writeTableSection(Tables); // Skip the "memory" section; we import the memory instead. writeTagSection(Tags); writeGlobalSection(Globals); writeExportSection(Exports); const MCSymbol *IndirectFunctionTable = Asm.getContext().lookupSymbol("__indirect_function_table"); writeElemSection(cast_or_null(IndirectFunctionTable), TableElems); writeDataCountSection(); CodeSectionIndex = writeCodeSection(Asm, Layout, Functions); DataSectionIndex = writeDataSection(Layout); } // The Sections in the COMDAT list have placeholder indices (their index among // custom sections, rather than among all sections). Fix them up here. for (auto &Group : Comdats) { for (auto &Entry : Group.second) { if (Entry.Kind == wasm::WASM_COMDAT_SECTION) { Entry.Index += SectionCount; } } } for (auto &CustomSection : CustomSections) writeCustomSection(CustomSection, Asm, Layout); if (Mode != DwoMode::DwoOnly) { writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats); writeRelocSection(CodeSectionIndex, "CODE", CodeRelocations); writeRelocSection(DataSectionIndex, "DATA", DataRelocations); } writeCustomRelocSections(); if (ProducersSection) writeCustomSection(*ProducersSection, Asm, Layout); if (TargetFeaturesSection) writeCustomSection(*TargetFeaturesSection, Asm, Layout); // TODO: Translate the .comment section to the output. return W->OS.tell() - StartOffset; } std::unique_ptr llvm::createWasmObjectWriter(std::unique_ptr MOTW, raw_pwrite_stream &OS) { return std::make_unique(std::move(MOTW), OS); } std::unique_ptr llvm::createWasmDwoObjectWriter(std::unique_ptr MOTW, raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS) { return std::make_unique(std::move(MOTW), OS, DwoOS); }