Index: test/wasm/undefined-weak-call.ll =================================================================== --- /dev/null +++ test/wasm/undefined-weak-call.ll @@ -0,0 +1,112 @@ +; RUN: llc -filetype=obj %s -o %t.o +; RUN: wasm-ld --check-signatures --no-entry %t.o -o %t.wasm +; RUN: obj2yaml %t.wasm | FileCheck %s + +; Check that calling an undefined weak function generates an appropriate stub +; that will fail at runtime with "unreachable". + +target triple = "wasm32-unknown-unknown-wasm" + +declare extern_weak void @weakFunc1() +declare extern_weak void @weakFunc2() ; same signature +declare extern_weak void @weakFunc3(i32 %arg) ; different +declare extern_weak void @weakFunc4() ; should be GC'd as not called + +define i32 @callWeakFuncs() { + call void @weakFunc1() + call void @weakFunc2() + call void @weakFunc3(i32 2) + %addr1 = ptrtoint void ()* @weakFunc1 to i32 + %addr4 = ptrtoint void ()* @weakFunc4 to i32 + %sum = add i32 %addr1, %addr4 + ret i32 %sum +} + +; CHECK: --- !WASM +; CHECK-NEXT: FileHeader: +; CHECK-NEXT: Version: 0x00000001 +; CHECK-NEXT: Sections: +; CHECK-NEXT: - Type: TYPE +; CHECK-NEXT: Signatures: +; CHECK-NEXT: - Index: 0 +; CHECK-NEXT: ReturnType: I32 +; CHECK-NEXT: ParamTypes: +; CHECK-NEXT: - Index: 1 +; CHECK-NEXT: ReturnType: NORESULT +; CHECK-NEXT: ParamTypes: +; CHECK-NEXT: - Index: 2 +; CHECK-NEXT: ReturnType: NORESULT +; CHECK-NEXT: ParamTypes: +; CHECK-NEXT: - I32 +; CHECK-NEXT: - Type: FUNCTION +; CHECK-NEXT: FunctionTypes: [ 0, 1, 2, 1 ] +; CHECK-NEXT: - Type: TABLE +; CHECK-NEXT: Tables: +; CHECK-NEXT: - ElemType: ANYFUNC +; CHECK-NEXT: Limits: +; CHECK-NEXT: Flags: [ HAS_MAX ] +; CHECK-NEXT: Initial: 0x00000001 +; CHECK-NEXT: Maximum: 0x00000001 +; CHECK-NEXT: - Type: MEMORY +; CHECK-NEXT: Memories: +; CHECK-NEXT: - Initial: 0x00000002 +; CHECK-NEXT: - Type: GLOBAL +; CHECK-NEXT: Globals: +; CHECK-NEXT: - Index: 0 +; CHECK-NEXT: Type: I32 +; CHECK-NEXT: Mutable: true +; CHECK-NEXT: InitExpr: +; CHECK-NEXT: Opcode: I32_CONST +; CHECK-NEXT: Value: 66560 +; CHECK-NEXT: - Index: 1 +; CHECK-NEXT: Type: I32 +; CHECK-NEXT: Mutable: false +; CHECK-NEXT: InitExpr: +; CHECK-NEXT: Opcode: I32_CONST +; CHECK-NEXT: Value: 66560 +; CHECK-NEXT: - Index: 2 +; CHECK-NEXT: Type: I32 +; CHECK-NEXT: Mutable: false +; CHECK-NEXT: InitExpr: +; CHECK-NEXT: Opcode: I32_CONST +; CHECK-NEXT: Value: 1024 +; CHECK-NEXT: - Type: EXPORT +; CHECK-NEXT: Exports: +; CHECK-NEXT: - Name: memory +; CHECK-NEXT: Kind: MEMORY +; CHECK-NEXT: Index: 0 +; CHECK-NEXT: - Name: __heap_base +; CHECK-NEXT: Kind: GLOBAL +; CHECK-NEXT: Index: 1 +; CHECK-NEXT: - Name: __data_end +; CHECK-NEXT: Kind: GLOBAL +; CHECK-NEXT: Index: 2 +; CHECK-NEXT: - Name: callWeakFuncs +; CHECK-NEXT: Kind: FUNCTION +; CHECK-NEXT: Index: 0 +; CHECK-NEXT: - Type: CODE +; CHECK-NEXT: Functions: +; CHECK-NEXT: - Index: 0 +; CHECK-NEXT: Locals: +; CHECK-NEXT: Body: 10818080800010818080800041021082808080004180808080004180808080006A0B +; CHECK-NEXT: - Index: 1 +; CHECK-NEXT: Locals: +; CHECK-NEXT: Body: 000B +; CHECK-NEXT: - Index: 2 +; CHECK-NEXT: Locals: +; CHECK-NEXT: Body: 000B +; CHECK-NEXT: - Index: 3 +; CHECK-NEXT: Locals: +; CHECK-NEXT: Body: 0B +; CHECK-NEXT: - Type: CUSTOM +; CHECK-NEXT: Name: name +; CHECK-NEXT: FunctionNames: +; CHECK-NEXT: - Index: 0 +; CHECK-NEXT: Name: callWeakFuncs +; CHECK-NEXT: - Index: 1 +; CHECK-NEXT: Name: __undefined +; CHECK-NEXT: - Index: 2 +; CHECK-NEXT: Name: __undefined +; CHECK-NEXT: - Index: 3 +; CHECK-NEXT: Name: __wasm_call_ctors +; CHECK-NEXT: ... Index: wasm/Driver.cpp =================================================================== --- wasm/Driver.cpp +++ wasm/Driver.cpp @@ -323,6 +323,10 @@ for (InputFile *F : Files) Symtab->addFile(F); + // Add synthetic dummies for weak undefined functions. + if (!Config->Relocatable) + Symtab->handleWeakUndefines(); + // Make sure we have resolved all symbols. if (!Config->Relocatable && !Config->AllowUndefined) { Symtab->reportRemainingUndefines(); Index: wasm/InputFiles.cpp =================================================================== --- wasm/InputFiles.cpp +++ wasm/InputFiles.cpp @@ -65,14 +65,8 @@ uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const { switch (Reloc.Type) { case R_WEBASSEMBLY_TABLE_INDEX_I32: - case R_WEBASSEMBLY_TABLE_INDEX_SLEB: { - // The null case is possible, if you take the address of a weak function - // that's simply not supplied. - FunctionSymbol *Sym = getFunctionSymbol(Reloc.Index); - if (Sym->hasTableIndex()) - return Sym->getTableIndex(); - return 0; - } + case R_WEBASSEMBLY_TABLE_INDEX_SLEB: + return getFunctionSymbol(Reloc.Index)->getTableIndex(); case R_WEBASSEMBLY_MEMORY_ADDR_SLEB: case R_WEBASSEMBLY_MEMORY_ADDR_I32: case R_WEBASSEMBLY_MEMORY_ADDR_LEB: Index: wasm/MarkLive.cpp =================================================================== --- wasm/MarkLive.cpp +++ wasm/MarkLive.cpp @@ -73,8 +73,17 @@ InputChunk *C = Q.pop_back_val(); for (const WasmRelocation Reloc : C->getRelocations()) { - if (Reloc.Type != R_WEBASSEMBLY_TYPE_INDEX_LEB) - Enqueue(C->File->getSymbol(Reloc.Index)); + if (Reloc.Type == R_WEBASSEMBLY_TYPE_INDEX_LEB) + continue; + Symbol *Sym = C->File->getSymbol(Reloc.Index); + // Don't mark functions live if we're taking the address of a function + // that won't actually go in the function table (has index zero). This + // is the case for some synthetic functions. + if ((Reloc.Type == R_WEBASSEMBLY_TABLE_INDEX_SLEB || + Reloc.Type == R_WEBASSEMBLY_TABLE_INDEX_I32) && + cast(Sym)->hasNullTableIndex()) + continue; + Enqueue(Sym); } } Index: wasm/SymbolTable.h =================================================================== --- wasm/SymbolTable.h +++ wasm/SymbolTable.h @@ -42,11 +42,16 @@ std::vector ObjectFiles; + void handleWeakUndefines(); void reportRemainingUndefines(); ArrayRef getSymbols() const { return SymVector; } Symbol *find(StringRef Name); + ArrayRef getSyntheticFunctions() const { + return SyntheticFunctions; + } + Symbol *addDefinedFunction(StringRef Name, uint32_t Flags, InputFile *File, InputFunction *Function); Symbol *addDefinedData(StringRef Name, uint32_t Flags, InputFile *File, @@ -77,6 +82,7 @@ llvm::DenseMap SymMap; std::vector SymVector; + std::vector SyntheticFunctions; llvm::DenseMap Comdats; }; Index: wasm/SymbolTable.cpp =================================================================== --- wasm/SymbolTable.cpp +++ wasm/SymbolTable.cpp @@ -33,6 +33,42 @@ ObjectFiles.push_back(F); } +static const uint8_t UNREACHABLE_FN[] = { + 0x03 /* ULEB length */, 0x00 /* ULEB num locals */, + 0x00 /* opcode unreachable */, 0x0b /* opcode end */ +}; + +void SymbolTable::handleWeakUndefines() { + DenseMap UndefinedFunctions; + for (Symbol *Sym : SymVector) { + if (!Sym->isUndefined() || !Sym->isWeak()) + continue; + auto *FuncSym = dyn_cast(Sym); + if (!FuncSym) + continue; + + // It is possible for undefined functions not to have a signature (eg. if + // added via "--undefined"), but weak undefined ones do have a signature. + assert(FuncSym->getFunctionType()); + const WasmSignature &Sig = *FuncSym->getFunctionType(); + + // Add a synthetic dummy for weak undefined functions. These dummies will + // be GC'd if not used as the target of any "call" instructions. + InputFunction *&Func = UndefinedFunctions[Sig]; + if (!Func) { + Func = make(Sig, UNREACHABLE_FN, "__undefined"); + SyntheticFunctions.emplace_back(Func); + // Ensure it compares equal to the null pointer, and so that table relocs + // don't pull in the stub body (only call-operand relocs should do that). + Func->setTableIndex(0); + } + // Hide our dummy to prevent export, and mark as local since the name is + // not unique. + uint32_t Flags = WASM_SYMBOL_VISIBILITY_HIDDEN | WASM_SYMBOL_BINDING_LOCAL; + replaceSymbol(Sym, Sym->getName(), Flags, nullptr, Func); + } +} + void SymbolTable::reportRemainingUndefines() { SetVector Undefs; for (Symbol *Sym : SymVector) { Index: wasm/Symbols.h =================================================================== --- wasm/Symbols.h +++ wasm/Symbols.h @@ -62,6 +62,7 @@ bool isLocal() const; bool isWeak() const; bool isHidden() const; + uint32_t getFlags() const { return Flags; } // Returns the symbol name. StringRef getName() const { return Name; } @@ -122,6 +123,10 @@ // Set the table index of the symbol void setTableIndex(uint32_t Index); + bool hasNullTableIndex() const { + return hasTableIndex() && getTableIndex() == 0; + } + protected: FunctionSymbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F, const WasmSignature *Type) Index: wasm/Writer.cpp =================================================================== --- wasm/Writer.cpp +++ wasm/Writer.cpp @@ -725,15 +725,19 @@ void Writer::assignIndexes() { uint32_t FunctionIndex = NumImportedFunctions + InputFunctions.size(); + auto AddDefinedFunction = [&](InputFunction *Func) { + if (!Func->Live) + return; + InputFunctions.emplace_back(Func); + Func->setOutputIndex(FunctionIndex++); + }; for (ObjFile *File : Symtab->ObjectFiles) { DEBUG(dbgs() << "Functions: " << File->getName() << "\n"); - for (InputFunction *Func : File->Functions) { - if (!Func->Live) - continue; - InputFunctions.emplace_back(Func); - Func->setOutputIndex(FunctionIndex++); - } + for (InputFunction *Func : File->Functions) + AddDefinedFunction(Func); } + for (InputFunction *Func : Symtab->getSyntheticFunctions()) + AddDefinedFunction(Func); uint32_t TableIndex = kInitialTableOffset; auto HandleRelocs = [&](InputChunk *Chunk) {