feat: jumping to userspace (currently only in dbg command with infinit jmp to self loop

kernel/inc/arch/x86_64/gdt.h

@@ -37,4 +37,6 @@ typedef struct {
     u16 iomap_base;
 } __attribute__((packed)) TSS;
 
+extern TSS tss;
+
 void gdt_init();

kernel/inc/core/scheduler.h

@@ -8,9 +8,10 @@ typedef struct task {
     struct task* next;
     u32 id;
     u32 sleep_ticks;
-} task_t;
+    u64 kernel_stack_top;
+} task;
 
 void sched_init();
-task_t* sched_spawn(void(*entry)());
+task* sched_spawn(void(*entry)());
 u64 sched_next(u64 curr_rsp);
 void yield(u64 ticks);