Align the stack for callbacks into mingw code

src/common/Compiler.h

@@ -176,6 +176,14 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #define BREAKPOINT()
 #endif
 
+#if defined(__MINGW32__) && defined(__i386__)
+// On x86, GCC expects 16-byte stack alignment (used for SSE instructions), but MSVC only uses 4-byte alignment.
+// Therefore the stack needs to be adjusted whenever MSVC code calls into GCC code.
+#   define ALIGN_STACK_FOR_MINGW __attribute__((force_align_arg_pointer))
+#else
+#   define ALIGN_STACK_FOR_MINGW
+#endif
+
 // Compat macros
 #define QDECL
 #define INLINE inline

src/common/System.cpp

@@ -240,7 +240,7 @@ static const char *WindowsExceptionString(DWORD code)
 		return "Unknown exception";
 	}
 }
-static LONG WINAPI CrashHandler(PEXCEPTION_POINTERS ExceptionInfo)
+ ALIGN_STACK_FOR_MINGW static LONG WINAPI CrashHandler(PEXCEPTION_POINTERS ExceptionInfo)
 {
 	// Reset handler so that any future errors cause a crash
 	SetUnhandledExceptionFilter(nullptr);

src/engine/client/cl_irc.cpp

@@ -2533,7 +2533,7 @@ static HANDLE IRC_ThreadHandle = nullptr;
 IRC_SystemThreadProc
 ==================
 */
-static DWORD WINAPI IRC_SystemThreadProc( LPVOID )
+ ALIGN_STACK_FOR_MINGW static DWORD WINAPI IRC_SystemThreadProc( LPVOID )
 {
 	IRC_Thread();
 	return 0;

src/engine/framework/System.cpp

@@ -671,17 +671,9 @@ static void Init(int argc, char** argv)
 
 } // namespace Sys
 
-// GCC expects a 16-byte aligned stack but Windows only guarantees 4-byte alignment.
-// The MinGW startup code should be handling this but for some reason it isn't.
-#if defined(_WIN32) && defined(__GNUC__) && defined(__i386__)
-#define ALIGN_STACK __attribute__((force_align_arg_pointer))
-#else
-#define ALIGN_STACK
-#endif
-
-// Program entry point. On Windows, main is #defined to SDL_main which is
-// invoked by SDLmain.
-ALIGN_STACK int main(int argc, char** argv)
+// Program entry point. On Windows, main is #defined to SDL_main which is invoked by SDLmain.
+// This is why ALIGN_STACK_FOR_MINGW is needed (normally gcc would generate alignment code in main()).
+ALIGN_STACK_FOR_MINGW int main(int argc, char** argv)
 {
 	// Initialize the engine. Any errors here are fatal.
 	try {

src/engine/sys/sdl_glimp.cpp

@@ -75,7 +75,7 @@ static SDL_Thread *renderThread = nullptr;
 GLimp_RenderThreadWrapper
 ===============
 */
-static int GLimp_RenderThreadWrapper( void* )
+ALIGN_STACK_FOR_MINGW static int GLimp_RenderThreadWrapper( void* )
 {
 	// These printfs cause race conditions which mess up the console output
 	logger.Notice( "Render thread starting\n" );

src/shared/VMMain.cpp

@@ -97,7 +97,7 @@ void Sys::Error(Str::StringRef message)
 #ifdef BUILD_VM_IN_PROCESS
 
 // Entry point called in a new thread inside the existing process
-extern "C" DLLEXPORT void vmMain(Sys::OSHandle rootSocket)
+extern "C" DLLEXPORT ALIGN_STACK_FOR_MINGW void vmMain(Sys::OSHandle rootSocket)
 {
 	try {
 		try {