Add libc++abi Objective-C exception bridge for WebAssembly

CMakeLists.txt

@@ -111,7 +111,11 @@ set(libobjc_CXX_SRCS
 if (WIN32 AND NOT MINGW)
 	list(APPEND libobjc_CXX_SRCS eh_win32_msvc.cc)
 elseif (NOT MINGW)
-	list(APPEND libobjc_C_SRCS eh_personality.c)
+	if (LIBOBJC_WASM)
+		list(APPEND libobjc_CXX_SRCS objc_wasm_eh.cc)
+	else ()
+		list(APPEND libobjc_C_SRCS eh_personality.c)
+	endif ()
 endif ()
 
 find_package(tsl-robin-map)

objc_wasm_eh.cc

@@ -0,0 +1,141 @@
+#include <cxxabi.h>
+#include <typeinfo>
+#include "objc/runtime.h"
+#include "objc/objc-arc.h"
+#include "visibility.h"
+
+/* We build libobjc2 for WebAssembly with emscripten against the libc++abi.
+ * For now, we do not define a custom personality function and instead let Objective-C
+ * exceptions piggyback on C++ exceptions.
+ *
+ * For WebAssembly clang defaults to `__gxx_wasm_personality_v0` (as of August 2026),
+ * which redirects to `__gxx_personality_imp` (The C++ unwind phase handler).
+ * We therefore supply our own RTTI object derived from c++abi's internal
+ * type info class to override the `can_catch` method and handle unboxing/catching of
+ * Objective-C Exceptions correctly.
+ */
+namespace __cxxabiv1
+{
+
+// (Re)declare libc++abi's type info class, so we can derive from it.
+// This is a private implementation detail of libc++abi, so we need to keep it in sync.
+class __shim_type_info : public std::type_info
+{
+	protected:
+	explicit __shim_type_info(const char *name) : type_info(name) {}
+
+	public:
+	virtual ~__shim_type_info();
+	virtual void noop1() const;
+	virtual void noop2() const;
+	virtual bool can_catch(const __shim_type_info *thrownType,
+		void *&adjustedPtr) const = 0;
+};
+}
+
+namespace
+{
+static BOOL isKindOfClass(Class thrown, Class type)
+{
+	do
+	{
+		if (thrown == type)
+		{
+			return YES;
+		}
+		thrown = class_getSuperclass(thrown);
+	} while (Nil != thrown);
+	return NO;
+}
+
+static id thrownObject(void *pointer)
+{
+	return *static_cast<id *>(pointer);
+}
+
+static void *releaseThrownObject(void *pointer)
+{
+	objc_release(thrownObject(pointer));
+	return pointer;
+}
+}  // namespace
+
+namespace gnustep {
+namespace libobjc {
+struct OBJC_PUBLIC __objc_type_info : __cxxabiv1::__shim_type_info
+{
+	explicit __objc_type_info(const char *name) : __shim_type_info(name) {}
+};
+
+struct OBJC_PUBLIC __objc_id_type_info : __objc_type_info
+{
+	__objc_id_type_info() : __objc_type_info("@id") {}
+	bool can_catch(const __cxxabiv1::__shim_type_info *thrownType,
+		void *&adjustedPtr) const override;
+};
+
+struct OBJC_PUBLIC __objc_class_type_info : __objc_type_info
+{
+	using __objc_type_info::__objc_type_info;
+	bool can_catch(const __cxxabiv1::__shim_type_info *thrownType,
+		void *&adjustedPtr) const override;
+};
+
+bool __objc_id_type_info::can_catch(
+	const __cxxabiv1::__shim_type_info *thrownType, void *&adjustedPtr) const
+{
+	if (dynamic_cast<const __objc_type_info *>(thrownType) == nullptr)
+	{
+		return false;
+	}
+	adjustedPtr = thrownObject(adjustedPtr);
+	return true;
+}
+
+bool __objc_class_type_info::can_catch(
+	const __cxxabiv1::__shim_type_info *thrownType, void *&adjustedPtr) const
+{
+	if (dynamic_cast<const __objc_type_info *>(thrownType) == nullptr)
+	{
+		return false;
+	}
+	// TODO: Apple compat/non-compat behavior
+	id thrown = thrownObject(adjustedPtr);
+	Class caughtClass = (Class)objc_getClass(name());
+	if (nil == thrown || Nil == caughtClass ||
+		!isKindOfClass(object_getClass(thrown), caughtClass))
+	{
+		return false;
+	}
+	adjustedPtr = thrown;
+	return true;
+}  // namespace libobjc
+}  // namespace gnustep
+
+extern "C"
+{
+OBJC_PUBLIC gnustep::libobjc::__objc_id_type_info __objc_id_type_info;
+
+static bool AppleCompatibleMode = true;
+OBJC_PUBLIC int objc_set_apple_compatible_objcxx_exceptions(int newValue)
+{
+	bool oldValue = AppleCompatibleMode;
+	AppleCompatibleMode = newValue;
+	return oldValue;
+}
+
+OBJC_PUBLIC __attribute__((noreturn)) void objc_exception_throw(id object)
+{
+	objc_retain(object);
+	id *exception = static_cast<id *>(
+		__cxxabiv1::__cxa_allocate_exception(sizeof(id)));
+	*exception = object;
+	__cxxabiv1::__cxa_throw(exception, &__objc_id_type_info,
+		releaseThrownObject);
+}
+
+OBJC_PUBLIC __attribute__((noreturn)) void objc_exception_rethrow(void)
+{
+	__cxxabiv1::__cxa_rethrow();
+}
+}