OSDev.org

Code: Select all

int* stack = (int*)kmalloc(512);  //setup 512 byte size stack 

/* 512 bytes give space for 128 values on the stack - we will have 15 values on the stack - the stack grows to smaller addresses therefore goto stacktop*/

stack+=113;                           

stack[0]=0x10; //es
stack[1]=0x10; //ds
stack[2]=0x10; //fs
stack[3]=0x10; //gs
stack[4]=0;    //edi
stack[5]=0;    //esi
stack[6]=0;    //ebp
stack[7]=0;    //esp
stack[8]=0;    //ebx
stack[9]=0;    //edx
stack[10]=0;    //ecx
stack[11]=0;    //eax
stack[12]=(uint)entry; //entry point  
stack[13]=0x08;
stack[14]=0x0202;

task->p_kstack = (uint)stack+14;  // stackend will be stacktop + pushed values

Code: Select all

void make_task(int pri, char *name, void (*entry)(), int ring)
{
    void *stack_mem;
    stack_data_t *stack;

    stack_mem = (unsigned int *)malloc(STACK_SIZE);
    stack_mem += STACK_SIZE - sizeof(stack_data_t);
    stack = stack_mem;
    if(ring == 0)
    {
        stack->gs = KERNEL_DATA_SEG;
        stack->fs = KERNEL_DATA_SEG;
        stack->es = KERNEL_DATA_SEG;
        stack->ds = KERNEL_DATA_SEG;
        stack->cs = KERNEL_CODE_SEG;
    }
    else
    {
        stack->gs = USER_DATA_SEG;
        stack->fs = USER_DATA_SEG;
        stack->es = USER_DATA_SEG;
        stack->ds = USER_DATA_SEG;
        stack->cs = USER_CODE_SEG;
    }    
    stack->edi = 0;
    stack->esi = 0;
    stack->esp = (unsigned int)stack;
    stack->ebp = stack->esp;
    stack->ebx = 0;
    stack->edx = 0;
    stack->ecx = 0;
    stack->eax = 0;
    stack->eip = (unsigned int)entry;
    stack->eflags = 0x00000202;
    
    strncpy(rrq[end].name, name, 32);
    rrq[end].stack = stack;
    rrq[end].ss = KERNEL_STACK_SEG;
    rrq[end].priority = pri;
    rrq[end].time = get_pri_time(pri);
    end++;
}

Code: Select all

_task_timer:
    push ss ; <------------- NEW -------------
    pushad
    push ds
    push es
    push fs
    push gs
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
;    cli
    push esp
    mov eax, _task_timer_c
    call eax
;    sti
    pop esp
    mov esp, eax
    pop gs
    pop fs
    pop es
    pop ds
    popad
    pop ss ; <------------- NEW -------------
    iretd

Code: Select all

set_a_gdt(5, (unsigned long)&TSS, sizeof(TSS) - 1, 0x89, 0x10);