Simple question about pingpong roottask

Hi,

  I have modified the pingpong root task, which come along the
Pistachio distribution, making it as simple as posible (file pasted at
the end). I have just kept creating a thread and starting it but there
is a point which I don't get at all.
  Why should the memory be touch by the root task before starting the
thread? I mean, why should any page fault been thrown when the new
thread is started?

  Thank you very much for your time.

Cheers,

  Gabriel Gonzalez.

<++>
#include <config.h>
#include <l4/kip.h>
#include <l4/ipc.h>
#include <l4/schedule.h>
#include <l4/kdebug.h>
#include <l4io.h>


L4_Word_t stack[2048] __attribute__ ((aligned (16)));

void pager (void)
{
  printf("PUMLALALAL");
}

int main (void)
{
    L4_Word_t control;
    L4_ThreadId_t master_tid, pager_tid;
    L4_Fpage_t kip_area, utcb_area;
    L4_Word_t utcb_size;
    L4_Time_t timeout;
    char c;

    L4_KernelInterfacePage_t * kip =
        (L4_KernelInterfacePage_t *) L4_KernelInterface ();
#ifdef TOUCH_MEM
    extern L4_Word_t _end, _start;
    for (L4_Word_t * x = (&_start); x < &_end; x++)
    {
        L4_Word_t q;
        q = *(volatile L4_Word_t*) x;
    }
#endif

    // Size for one UTCB
    utcb_size = L4_UtcbSize (kip);

    // Create pager
    master_tid = L4_Myself ();
    pager_tid = L4_GlobalId (L4_ThreadNo (master_tid) + 1, 2);

    // VU: calculate UTCB address -- this has to be revised
    L4_Word_t pager_utcb = L4_MyLocalId().raw;
    pager_utcb = (pager_utcb & ~(utcb_size - 1)) + utcb_size;
    printf("local id = %lx, pager UTCB = %lx\n", pager_tid,
           pager_utcb);

    printf("thread_control: %d\n",
           L4_ThreadControl (pager_tid, L4_Myself (), L4_Myself (),
                             L4_Myself(), (void*)pager_utcb));
    L4_Start (pager_tid, (L4_Word_t) stack + sizeof(stack) - 32,
(L4_Word_t)pager);

    printf("Stack %p\n", stack + sizeof(stack) - 32);
    printf("pager IP %p\n", pager);

    c = getc();
    L4_LoadMR (0, 0);
    L4_Send (pager_tid);

    for (;;)
        L4_KDB_Enter ("EOW");
}
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