Fix fork() for new task switching model

src/drivers/nulldrv/main.cpp

@@ -16,11 +16,9 @@ int
 main(int argc, const char **argv)
 {
 	int32_t pid = getpid();
+	int32_t child = fork();
 	message("hello from nulldrv!");
-	//int32_t child = fork();
-	//debug();
 	for (int i = 1; i < 5; ++i)
 		sleep(i*10);
-	debug();
 	return 0;
 }

src/drivers/nulldrv/main.s

@@ -44,7 +44,7 @@ fork:
 	push rbp
 	mov rbp, rsp
 
-	mov rax, 0x00
+	mov rax, 0x03
 	syscall    ; pid left in rax
 
 	pop rbp