fix: thread switch gets back into the isr routine but iret does not return to the correct frame

src/kernel.c

@@ -48,5 +48,6 @@ void kernel_main(multiboot_info_t *mbd, uint32_t magic)
 	create_process(1);
 	create_thread(current_pcb, shell_init);
 	toris();
-	while (true);
+	while (true)
+		;
 }

src/multitasking/switch_to_thread.s

@@ -4,11 +4,9 @@
 	.global switch_thread
 
 switch_thread:
-	push ebx
-	push ebp
-	push edi
-	push esi
-
+	mov edx, DWORD PTR [esp]
+	cmp DWORD PTR [current_tcb], 0
+	je .LABEL1
 	mov eax, [current_tcb]
 
 	// save the current stack pointer to the old stack
@@ -16,6 +14,7 @@ switch_thread:
 
 	// stack pointer + the 4 regs pushed
 	// and + 1 to get the argument (next thread)
+.LABEL1:
 	mov esi, [esp+(4+1)*4]
 	mov [current_tcb], esi
 
@@ -23,9 +22,6 @@ switch_thread:
 
 	mov esp, [eax+0] // get esp
 
-	pop esi
-	pop edi
-	pop ebp
-	pop ebx
-
-	iret 
+	push edx
+	
+	ret

src/multitasking/thread.c

@@ -22,19 +22,18 @@ struct tcb *create_thread(struct pcb *process, void (*routine)(void))
 	// set esp to "skip" the 4 GPRs and eip later to be used as the context
 	// of the thread
 	new_tcb->esp = new_tcb->esp0 + STACK_SIZE - 5 * 4;
-	memcpy(new_tcb->esp + 4, routine, 4);
+	new_tcb->esp[4] = (uint32_t)routine;
 	new_tcb->process = process;
 	new_tcb->next = NULL;
 	new_tcb->state = NEW;
 
-	struct tcb *it = process->thread_list;
-	if (it) {
-		while (it)
-			it = it->next;
-		it = new_tcb;
-	}
-	else {
+	if (process->thread_list == NULL) {
 		process->thread_list = new_tcb;
+	} else {
+		struct tcb *it = process->thread_list;
+		while (it->next)
+			it = it->next;
+		it->next = new_tcb;
 	}
 
 	return new_tcb;