Kernel stack grows on each context switch

[Crupette]

As per the title, every time the kernel switches the current process, the stack grows by exactly 28 bytes if the process is a user mode process. I have no idea what is causing this, and all of my debugging efforts have come up empty. I have no idea what is causing this, and the only fix I have come up with so far is to manually change TSS.ESP0 by adding 28.

Should this be happening, or am I doing something stupid that I didn't realize?

common IRQ handler:

Code: Select all

irq_common:
	pusha
	push ds
	push es
	push fs
	push gs
	
	mov ax, 0x10
	mov ds, ax
	mov es, ax
	mov fs, ax
	mov gs, ax
	cld
	
	push esp
	call irq_intHandler
	add esp, 4
	
	pop gs
	pop fs
	pop es
	pop ds
	popa

	add esp, 8
	
	iret
}

process switcher:

Code: Select all

void switchTask(regs_t *r){
	if(processList == NULL) return;
	if(processList->size <= 1) return;

	memcpy(&(currentProcess->task->state), r, sizeof(regs_t));

switchTask_nextproc:
	nextProcess = nextProcess->next;
	if(nextProcess == NULL){
		nextProcess = processList->tail;	
	}
	currentProcess = nextProcess->data;
	if(currentProcess->sleepCounter > 0){
		goto switchTask_nextproc;
	}
	
	memcpy(r, &(currentProcess->task->state), sizeof(regs_t));
	
	pg_switchDir(currentProcess->task->dir);	

	tss_setStack(r->esp);
}

Any help would be greatly appreciated

[dropje]

Code: Select all

tss_setStack(r->esp);

r->esp in this call appears to be the value of ESP at the time of your PUSHA instruction, i.e. after (user)ss, (user)esp, eflags, cs, eip, err and num (28 bytes) have been pushed on the kernel stack. The next interrupt frame will be placed on top of this.

I think you should be able to set the TSS esp to the bottom of the kernel stack of the task you are switching to: there shouldn't be any code running on that stack when you are back in user-mode.

[Crupette]

Thank you for your help!
I fixed my problem by adding a kstack_bottom variable to the task, and setting the TSS.ESP0 to the variable
at least I learned more about being careful with the stack