[Kernel] Fix spontaneous r0 corruption

src/core/kernel/events.cpp

@@ -111,12 +111,15 @@ void Kernel::svcClearEvent() {
 void Kernel::svcSignalEvent() {
 	const Handle handle = regs[0];
 	logSVC("SignalEvent(event handle = %X)\n", handle);
-	
+	KernelObject* object = getObject(handle, KernelObjectType::Event);
-	if (!signalEvent(handle)) {
+
+	if (object == nullptr) {
 		Helpers::panic("Signalled non-existent event: %X\n", handle);
 		regs[0] = SVCResult::BadHandle;
 	} else {
+		// We must signalEvent after setting r0, otherwise the r0 of the new thread will ne corrupted
 		regs[0] = SVCResult::Success;
+		signalEvent(handle);
 	}
 }
 

src/core/kernel/ports.cpp

@@ -78,24 +78,26 @@ void Kernel::sendSyncRequest() {
 
 	// The sync request is being sent at a service rather than whatever port, so have the service manager intercept it
 	if (KernelHandles::isServiceHandle(handle)) {
-		serviceManager.sendCommandToService(messagePointer, handle);
+		// The service call might cause a reschedule and change threads. Hence, set r0 before executing the service call
+		// Because if the service call goes first, we might corrupt the new thread's r0!!
 		regs[0] = SVCResult::Success;
+		serviceManager.sendCommandToService(messagePointer, handle);
 		return;
 	}
 
 	// Check if our sync request is targetting a file instead of a service
 	bool isFileOperation = getObject(handle, KernelObjectType::File) != nullptr;
 	if (isFileOperation) {
+		regs[0] = SVCResult::Success; // r0 goes first here too
 		handleFileOperation(messagePointer, handle);
-		regs[0] = SVCResult::Success;
 		return;
 	}
 
 	// Check if our sync request is targetting a directory instead of a service
 	bool isDirectoryOperation = getObject(handle, KernelObjectType::Directory) != nullptr;
 	if (isDirectoryOperation) {
+		regs[0] = SVCResult::Success; // r0 goes first here too
 		handleDirectoryOperation(messagePointer, handle);
-		regs[0] = SVCResult::Success;
 		return;
 	}
 
@@ -111,13 +113,13 @@ void Kernel::sendSyncRequest() {
 	const Handle portHandle = sessionData->portHandle;
 
 	if (portHandle == srvHandle) { // Special-case SendSyncRequest targetting the "srv: port"
+		regs[0] = SVCResult::Success;
 		serviceManager.handleSyncRequest(messagePointer);
 	} else if (portHandle == errorPortHandle) { // Special-case "err:f" for juicy logs too
+		regs[0] = SVCResult::Success;
 		handleErrorSyncRequest(messagePointer);
 	} else {
 		const auto portData = objects[portHandle].getData<Port>();
 		Helpers::panic("SendSyncRequest targetting port %s\n", portData->name);
 	}
-
-	regs[0] = SVCResult::Success;
 }