MCSymbol *WebAssemblyMCInstLower::GetExternalSymbolSymbol(
const MachineOperand &MO) const {
const char *Name = MO.getSymbolName();
MCSymbolWasm *WasmSym =
cast<MCSymbolWasm>(Printer.GetExternalSymbolSymbol(Name));
const WebAssemblySubtarget &Subtarget = Printer.getSubtarget();
// Except for the two exceptions (__stack_pointer and __cpp_exception), all
// other external symbols used by CodeGen are functions. It's OK to hardcode
// knowledge of specific symbols here; this method is precisely there for
// fetching the signatures of known Clang-provided symbols.
if (strcmp(Name, "__stack_pointer") == 0) {
WasmSym->setType(wasm::WASM_SYMBOL_TYPE_GLOBAL);
WasmSym->setGlobalType(wasm::WasmGlobalType{
uint8_t(Subtarget.hasAddr64() ? wasm::WASM_TYPE_I64
: wasm::WASM_TYPE_I32),
true});
return WasmSym;
}
SmallVector<wasm::ValType, 4> Returns;
SmallVector<wasm::ValType, 4> Params;
if (strcmp(Name, "__cpp_exception") == 0) {
WasmSym->setType(wasm::WASM_SYMBOL_TYPE_EVENT);
// We can't confirm its signature index for now because there can be
// imported exceptions. Set it to be 0 for now.
WasmSym->setEventType(
{wasm::WASM_EVENT_ATTRIBUTE_EXCEPTION, /* SigIndex */ 0});
// We may have multiple C++ compilation units to be linked together, each of
// which defines the exception symbol. To resolve them, we declare them as
// weak.
WasmSym->setWeak(true);
WasmSym->setExternal(true);
// All C++ exceptions are assumed to have a single i32 (for wasm32) or i64
// (for wasm64) param type and void return type. The reaon is, all C++
// exception values are pointers, and to share the type section with
// functions, exceptions are assumed to have void return type.
Params.push_back(Subtarget.hasAddr64() ? wasm::ValType::I64
: wasm::ValType::I32);
} else { // Function symbols
WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
GetLibcallSignature(Subtarget, Name, Returns, Params);
}
auto Signature =
make_unique<wasm::WasmSignature>(std::move(Returns), std::move(Params));
WasmSym->setSignature(Signature.get());
Printer.addSignature(std::move(Signature));
return WasmSym;
}
