MinGW: Use _Unwind_RaiseException to throw exceptions (#278)

The current implementation uses Vectored Exception Handlers. This implementation is too greedy, and invokes _objc_unexpected_exception for (certain) exceptions which would be handled by the application itself.

Author: qmfrederik

CMakeLists.txt

@@ -124,9 +124,7 @@ 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 ()
+elseif (NOT MINGW)
 	list(APPEND libobjc_C_SRCS eh_personality.c)
 endif ()
 
@@ -230,7 +228,7 @@ 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)
+	list(APPEND libobjc_CXX_SRCS objcxx_eh.cc objcxx_eh_mingw.cc)
 else ()
 	separate_arguments(EH_PERSONALITY_FLAGS NATIVE_COMMAND ${CMAKE_CXX_FLAGS})
 	if (CMAKE_CXX_COMPILER_TARGET)

eh_win32_mingw.m

@@ -1,19 +1,11 @@
-typedef struct objc_object* id;
 #include <atomic>
 #include <stdlib.h>
 #include <stdio.h>
 #include "dwarf_eh.h"
+#include "objcxx_eh_private.h"
 #include "objcxx_eh.h"
-#include "visibility.h"
-#include "objc/runtime.h"
 #include "objc/objc-arc.h"
 
-#ifndef DEBUG_EXCEPTIONS
-#define DEBUG_LOG(...)
-#else
-#define DEBUG_LOG(str, ...) fprintf(stderr, str, ## __VA_ARGS__)
-#endif
-
 /**
  * Helper function that has a custom personality function.
  * This calls `cxx_throw` and has a destructor that must be run.  We intercept
@@ -23,92 +15,8 @@ int eh_trampoline();
 
 uint64_t cxx_exception_class;
 
-/**
- * Our own definitions of C++ ABI functions and types.  These are provided
- * because this file must not include cxxabi.h.  We need to handle subtly
- * different variations of the ABI and including one specific implementation
- * would make that very difficult.
- */
-namespace __cxxabiv1
-{
-	/**
-	 * Type info for classes.  Forward declared because the GNU ABI provides a
-	 * method on all type_info objects that the dynamic the dynamic cast header
-	 * needs.
-	 */
-	struct __class_type_info;
-	/**
-	 * The C++ in-flight exception object.  We will derive the offset of fields
-	 * in this, so we do not ever actually see a concrete definition of it.
-	 */
-	struct __cxa_exception;
-	/**
-	 * The public ABI structure for current exception state.
-	 */
-	struct __cxa_eh_globals
-	{
-		/**
-		 * The current exception that has been caught.
-		 */
-		__cxa_exception *caughtExceptions;
-		/**
-		 * The number of uncaught exceptions still in flight.
-		 */
-		unsigned int uncaughtExceptions;
-	};
-	/**
-	 * Retrieve the above structure.
-	 */
-	extern "C" __cxa_eh_globals *__cxa_get_globals();
-}
-
-namespace std
-{
-	struct type_info;
-}
-
 using namespace __cxxabiv1;
 
-// Define some C++ ABI types here, rather than including them.  This prevents
-// conflicts with the libstdc++ headers, which expose only a subset of the
-// type_info class (the part required for standards compliance, not the
-// implementation details).
-
-typedef void (*unexpected_handler)();
-typedef void (*terminate_handler)();
-
-namespace std
-{
-	/**
-	 * std::type_info, containing the minimum requirements for the ABI.
-	 * Public headers on some implementations also expose some implementation
-	 * details.  The layout of our subclasses must respect the layout of the
-	 * C++ runtime library, but also needs to be portable across multiple
-	 * implementations and so should not depend on internal symbols from those
-	 * libraries.
-	 */
-	class type_info
-	{
-				public:
-				virtual ~type_info();
-				bool operator==(const type_info &) const;
-				bool operator!=(const type_info &) const;
-				bool before(const type_info &) const;
-				type_info();
-				private:
-				type_info(const type_info& rhs);
-				type_info& operator= (const type_info& rhs);
-				const char *__type_name;
-				protected:
-				type_info(const char *name): __type_name(name) { }
-				public:
-				const char* name() const { return __type_name; }
-	};
-}
-
-extern "C" void __cxa_throw(void*, std::type_info*, void(*)(void*));
-extern "C" void __cxa_rethrow();
-
 namespace
 {
 /**
@@ -140,49 +48,6 @@ std::atomic<ptrdiff_t> type_info_offset;
  */
 std::atomic<size_t> exception_struct_size;
 
-/**
- * Helper function to find a particular value scanning backwards in a
- * structure.
- */
-template<typename T>
-ptrdiff_t find_backwards(void *addr, T val)
-{
-	T *ptr = reinterpret_cast<T*>(addr);
-	for (ptrdiff_t disp = -1 ; (disp * sizeof(T) > -128) ; disp--)
-	{
-		if (ptr[disp] == val)
-		{
-			return disp * sizeof(T);
-		}
-	}
-	fprintf(stderr, "Unable to find field in C++ exception structure\n");
-	abort();
-}
-
-/**
- * Helper function to find a particular value scanning forwards in a
- * structure.
- */
-template<typename T>
-ptrdiff_t find_forwards(void *addr, T val)
-{
-	T *ptr = reinterpret_cast<T*>(addr);
-	for (ptrdiff_t disp = 0 ; (disp * sizeof(T) < 256) ; disp++)
-	{
-		if (ptr[disp] == val)
-		{
-			return disp * sizeof(T);
-		}
-	}
-	fprintf(stderr, "Unable to find field in C++ exception structure\n");
-	abort();
-}
-
-template<typename T>
-T *pointer_add(void *ptr, ptrdiff_t offset)
-{
-	return reinterpret_cast<T*>(reinterpret_cast<char*>(ptr) + offset);
-}
 
 /**
  * Exception cleanup function for C++ exceptions that wrap Objective-C
@@ -225,76 +90,33 @@ namespace gnustep
 {
 	namespace libobjc
 	{
-		/**
-		 * Superclass for the type info for Objective-C exceptions.
-		 */
-		struct OBJC_PUBLIC __objc_type_info : std::type_info
-		{
-			/**
-			 * Constructor that sets the name.
-			 */
-			__objc_type_info(const char *name) : type_info(name) {}
-			/**
-			 * Helper function used by libsupc++ and libcxxrt to determine if
-			 * this is a pointer type.  If so, catches automatically
-			 * dereference the pointer to the thrown pointer in
-			 * `__cxa_begin_catch`.
-			 */
-			virtual bool __is_pointer_p() const { return true; }
-			/**
-			 * Helper function used by libsupc++ and libcxxrt to determine if
-			 * this is a function pointer type.  Irrelevant for our purposes.
-			 */
-			virtual bool __is_function_p() const { return false; }
-			/**
-			 * Catch handler.  This is used in the C++ personality function.
-			 * `thrown_type` is the type info of the thrown object, `this` is
-			 * the type info at the catch site.  `thrown_object` is a pointer
-			 * to a pointer to the thrown object and may be adjusted by this
-			 * function.
-			 */
-			virtual bool __do_catch(const type_info *thrown_type,
+		__objc_type_info::__objc_type_info(const char *name) : type_info(name) {}
+
+		bool __objc_type_info::__is_pointer_p() const { return true; }
+
+		bool __objc_type_info::__is_function_p() const { return false; }
+
+		bool __objc_type_info::__do_catch(const type_info *thrown_type,
 			                        void **thrown_object,
 			                        unsigned) const
-			{
-				assert(0);
-				return false;
-			};
-			/**
-			 * Function used for `dynamic_cast` between two C++ class types in
-			 * libsupc++ and libcxxrt.
-			 *
-			 * This should never be called on Objective-C types.
-			 */
-			virtual bool __do_upcast(
+		{
+			assert(0);
+			return false;
+		};
+
+		bool __objc_type_info::__do_upcast(
 			                const __class_type_info *target,
 			                void **thrown_object) const
-			{
-				return false;
-			};
+		{
+			return false;
 		};
+		
+		
 		/**
-		 * Singleton type info for the `id` type.
+		 * The `id` type is mangled to `@id`, which is not a valid mangling
+		 * of anything else.
 		 */
-		struct OBJC_PUBLIC __objc_id_type_info : __objc_type_info
-		{
-			/**
-			 * The `id` type is mangled to `@id`, which is not a valid mangling
-			 * of anything else.
-			 */
-			__objc_id_type_info() : __objc_type_info("@id") {};
-			virtual ~__objc_id_type_info();
-			virtual bool __do_catch(const type_info *thrownType,
-			                        void **obj,
-			                        unsigned outer) const;
-		};
-		struct OBJC_PUBLIC __objc_class_type_info : __objc_type_info
-		{
-			virtual ~__objc_class_type_info();
-			virtual bool __do_catch(const type_info *thrownType,
-			                        void **obj,
-			                        unsigned outer) const;
-		};
+		__objc_id_type_info::__objc_id_type_info() : __objc_type_info("@id") {};
 	}
 
 	static inline id dereference_thrown_object_pointer(void** obj) {
@@ -430,29 +252,7 @@ void* objc_object_for_cxx_exception(void *thrown_exception, int *isValid)
 } // extern "C"
 
 
-/**
- * C++ structure that is thrown through a frame with the `test_eh_personality`
- * personality function.  This contains a well-known value that we can search
- * for after the unwind header.
- */
-struct
-PRIVATE
-MagicValueHolder
-{
-	/**
-	 * The constant that we will search for to identify this object.
-	 */
-	static constexpr uint32_t magic = 0x01020304;
-	/**
-	 * The single field in this structure.
-	 */
-	uint32_t magic_value;
-	/**
-	 * Constructor.  Initialises the field with the magic constant.
-	 */
-	MagicValueHolder() { magic_value = magic; }
-};
-
+MagicValueHolder::MagicValueHolder() { magic_value = magic; }
 
 /**
  * Function that simply throws an instance of `MagicValueHolder`.
@@ -508,21 +308,4 @@ extern "C" void test_cxx_eh_implementation()
 	}
 	assert(caught);
 }
-#else
-static void eh_cleanup(void *exception)
-{
-	DEBUG_LOG("eh_cleanup: Releasing 0x%x\n", *(id*)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);
-	DEBUG_LOG("objc_exception_throw: Throwing 0x%x\n", *exc);
-	__cxa_throw(exc, & __objc_id_type_info, eh_cleanup);
-}
 #endif