Use C++ exceptions unconditionally for Objective-C[++] on MinGW (#267)

CMakeLists.txt

@@ -117,9 +117,11 @@ set(libobjc_CXX_SRCS
 # Windows does not use DWARF EH, except when using the GNU ABI (MinGW)
 if (WIN32 AND NOT MINGW)
 	list(APPEND libobjc_CXX_SRCS eh_win32_msvc.cc)
+elseif (MINGW)
+	list(APPEND libobjc_CXX_SRCS eh_win32_mingw.m)
 else ()
 	list(APPEND libobjc_C_SRCS eh_personality.c)
-endif (WIN32 AND NOT MINGW)
+endif ()
 
 find_package(tsl-robin-map)
 
@@ -132,7 +134,7 @@ if (NOT tls-robin-map_FOUND)
 	FetchContent_MakeAvailable(robinmap)
 endif()
 
-if (WIN32 AND NOT MINGW)
+if (WIN32)
 	set(OLD_ABI_COMPAT_DEFAULT false)
 else()
 	set(OLD_ABI_COMPAT_DEFAULT true)
@@ -211,6 +213,9 @@ endif()
 
 if (WIN32 AND NOT MINGW)
 	message(STATUS "Using MSVC-compatible exception model")
+elseif (MINGW)
+	message(STATUS "Using MinGW-compatible exception model")
+	list(APPEND libobjc_CXX_SRCS objcxx_eh.cc)
 else ()
 	separate_arguments(EH_PERSONALITY_FLAGS NATIVE_COMMAND ${CMAKE_CXX_FLAGS})
 	if (CMAKE_CXX_COMPILER_TARGET)

Test/UnexpectedException.m

@@ -8,19 +8,20 @@
 #include <Windows.h>
 #endif
 
-id exceptionObj = @"Exception";
+id expectedExceptionObj = @"ExpectedException";
+id unexpectedExceptionObj = @"UnexpectedException";
 
 void _UncaughtExceptionHandler(id exception)
 {
-	assert(exception == exceptionObj);
+	assert(exception == unexpectedExceptionObj);
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW32__)
 	// on Windows we will exit in _UnhandledExceptionFilter() below
 #else
 	exit(0);
 #endif
 }
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW32__)
 LONG WINAPI _UnhandledExceptionFilter(struct _EXCEPTION_POINTERS* exceptionInfo)
 {
 	assert(exceptionInfo != NULL);
@@ -30,18 +31,26 @@ LONG WINAPI _UnhandledExceptionFilter(struct _EXCEPTION_POINTERS* exceptionInfo)
 
 int main(void)
 {
-	#if !(defined(__arm__) || defined(__ARM_ARCH_ISA_A64))
+#if !(defined(__arm__) || defined(__ARM_ARCH_ISA_A64))
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW32__)
 	// also verify that an existing handler still gets called after we set ours
 	SetUnhandledExceptionFilter(&_UnhandledExceptionFilter);
 #endif
+	@try
+	{
+		@throw expectedExceptionObj;
+	}
+	@catch(id exception)
+	{
+		assert(exception == expectedExceptionObj);
+	}
 
 	objc_setUncaughtExceptionHandler(_UncaughtExceptionHandler);
-	@throw exceptionObj;
+	@throw unexpectedExceptionObj;
 	assert(0 && "should not be reached!");
 
 	return -1;
-	#endif
+#endif
 	// FIXME: Test currently fails on ARM and AArch64
 	return 77; // Skip test
 }

eh_win32_mingw.m

@@ -0,0 +1,59 @@
+#include "objc/runtime.h"
+#include "objc/objc-exception.h"
+#include "objc/hooks.h"
+#include <stdio.h>
+
+#include <windows.h>
+
+#define STATUS_GCC_THROW 0x20474343
+
+extern void *__cxa_current_exception_type(void);
+extern void __cxa_rethrow();
+
+BOOL handler_installed = NO;
+_Thread_local BOOL in_handler = NO;
+
+// This vectored exception handler is the last handler to get invoke for every exception (Objective C or foreign).
+// It calls _objc_unexpected_exception only when the exception is a C++ exception (ex->ExceptionCode == STATUS_GCC_THROW)
+// and the exception is an Objective C exception.
+// It always returns EXCEPTION_CONTINUE_SEARCH, so Windows will continue handling the exception.
+static LONG CALLBACK _objc_vectored_exception_handler(EXCEPTION_POINTERS* exceptionInfo)
+{
+	const EXCEPTION_RECORD* ex = exceptionInfo->ExceptionRecord;
+
+	if (_objc_unexpected_exception != 0
+		&& ex->ExceptionCode == STATUS_GCC_THROW
+		&& !in_handler)
+	{
+		// Rethrow the current exception and use the @catch clauses to determine whether it's an Objective C exception
+		// or a foreign exception.
+		if (__cxa_current_exception_type()) {
+			in_handler = YES;
+			@try {
+				__cxa_rethrow();
+			} @catch (id e) {
+				// Invoke _objc_unexpected_exception for Objective C exceptions
+				(*_objc_unexpected_exception)((id)e);
+			} @catch (...) {
+				// Ignore foreign exceptions.
+			}
+			in_handler = NO;
+		}
+	}
+
+	// EXCEPTION_CONTINUE_SEARCH instructs the exception handler to continue searching for appropriate exception handlers.
+	return EXCEPTION_CONTINUE_SEARCH;
+}
+
+OBJC_PUBLIC extern objc_uncaught_exception_handler objc_setUncaughtExceptionHandler(objc_uncaught_exception_handler handler)
+{
+	objc_uncaught_exception_handler previousHandler = __atomic_exchange_n(&_objc_unexpected_exception, handler, __ATOMIC_SEQ_CST);
+
+	// Add a vectored exception handler to support the hook. We only need to do this once.
+	if (!handler_installed) {
+		AddVectoredExceptionHandler(0 /* The handler is the last handler to be called */ , _objc_vectored_exception_handler);
+		handler_installed = YES;
+	}
+
+	return previousHandler;
+}

objcxx_eh.cc

@@ -6,6 +6,7 @@ typedef struct objc_object* id;
 #include "objcxx_eh.h"
 #include "visibility.h"
 #include "objc/runtime.h"
+#include "objc/objc-arc.h"
 
 /**
  * Helper function that has a custom personality function.
@@ -99,6 +100,9 @@ namespace std
 	};
 }
 
+extern "C" void __cxa_throw(void*, std::type_info*, void(*)(void*));
+extern "C" void __cxa_rethrow();
+
 namespace
 {
 /**
@@ -340,6 +344,7 @@ bool gnustep::libobjc::__objc_class_type_info::__do_catch(const type_info *throw
 	{
 		*obj = (void*)thrown;
 	}
+
 	return found;
 };
 
@@ -369,7 +374,7 @@ extern "C"
 /**
  * The public symbol that the compiler uses to indicate the Objective-C id type.
  */
-gnustep::libobjc::__objc_id_type_info __objc_id_type_info;
+OBJC_PUBLIC gnustep::libobjc::__objc_id_type_info __objc_id_type_info;
 
 struct _Unwind_Exception *objc_init_cxx_exception(id obj)
 {
@@ -468,6 +473,7 @@ BEGIN_PERSONALITY_FUNCTION(test_eh_personality)
  * personality function, allowing us to inspect a C++ exception that is in a
  * known state.
  */
+#ifndef __MINGW32__
 extern "C" void test_cxx_eh_implementation()
 {
 	if (done_setup)
@@ -485,4 +491,19 @@ extern "C" void test_cxx_eh_implementation()
 	}
 	assert(caught);
 }
+#else
+static void eh_cleanup(void *exception)
+{
+	objc_release(*(id*)exception);
+}
 
+extern "C"
+OBJC_PUBLIC
+void objc_exception_throw(id object)
+{
+	id *exc = (id *)__cxa_allocate_exception(sizeof(id));
+	*exc = object;
+	objc_retain(object);
+	__cxa_throw(exc, & __objc_id_type_info, eh_cleanup);
+}
+#endif