Re: [Xenomai-help] Howto catch SEGV signals in Xenomai

[Philippe Gerum <rpm@xenomai.org>]

On Tue, 2007-03-13 at 16:25 +0100, Gilles Chanteperdrix wrote:
> M. Koehrer wrote:
> > Hi all,
> > 
> > I have a problem to catch segment violations with Xenomai:
> > For demonstration I use the following program:
> > ------------------------------------------
> > #include <stdio.h>
> > #include <sys/mman.h>
> > 
> > #include <native/task.h>
> > #include <native/sem.h>
> > RT_TASK taska_desc;
> > volatile int *pointer = 0;
> > 
> > void mytaska(void *cookie)
> > {
> >     int i;
> >     for (i=0; i < 50; i++)
> >     {
> >         rt_task_sleep(50000000);
> >         if (i > 20)
> >         {
> >             *pointer = 123;
> >         }
> >         printf("Hello %i\n", i);
> >     }
> >     printf("Hi, this is task A\n");
> > }
> > 
> > int main(void)
> > {
> >     mlockall(MCL_CURRENT|MCL_FUTURE);
> > 
> >     rt_task_create(&taska_desc, "mytaska", 0, 81, T_JOINABLE);
> >     rt_task_start(&taska_desc, &mytaska, NULL);
> > 
> >     rt_task_join(&taska_desc);
> >     printf("Main: A joined\n");
> > 
> >     return 0;
> > }
> > ---------------------------------------
> > Whenever i is greater than 20 a segment violation occurs, as I must not write
> > to address 0 (the pointer is always NULL).
> > However, what happens is, that my system freezes after printing out 18 or 19.
> > I have to reset the PC to continue.
> > When I write a printf() directly before the invalid assignment I get the usual linux
> > "segmentation fault" error message.
> > 
> > How can I catch a signal in a Xenomai real time task?
> > 
> > I am running Xenomai 2.3.0 + NOCOW patch.
> > 
> > I have enclosed the .c file and a Makefile in a .tgz file.
> > 
> > Thanks for any feedback on that issue
> 
> It looks like the "relaxing a kicked thread" issue again. Could you try
> the attached patch ?
> 

Gasp. This patch would contradict what's going on into
do_sigwake_event(); well, if you are right, we would have entered the
twilight zone with full ignition of the auxiliary boosters.

Btw, XNRELAX is a state bit, not an information one. i.e.

-               if (xnthread_test_info(thread, XNKICKED)) {
+               if (xnthread_test_info(thread, XNKICKED) && !xnthread_test_state(thread, XNRELAX)) {

-- 
Philippe.