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Date: Thu, 07 Jan 2010 18:26:45 +0100
From: Stefan Kisdaroczi <kisda@domain.hid>
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Subject: Re: [Xenomai-help] native skin 2.5.0: rt_task_create() segfaults if
 stacksize parameter too small
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: xenomai@xenomai.org

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Am 07.01.2010 17:57, schrieb Gilles Chanteperdrix:
> Stefan Kisdaroczi wrote:
>> Am 07.01.2010 15:36, schrieb Gilles Chanteperdrix:
>>> Stefan Kisdaroczi wrote:
>>>> hi,
>>>>
>>>> i have upgraded xenomai to 2.5.0 (x86,32bit). My application segfaul=
ts when I
>>>> try to create a task with stacksize 2048, this worked with 2.4.10.
>>>> Because my app is written in pascal i have reproduced the problem wi=
th the
>>>> xenomai trivial-periodic.c example:
>>>>
>>>> -	rt_task_create(&demo_task, "trivial", 0, 99, 0);
>>>> +	rt_task_create(&demo_task, "trivial",16911, 99, 0);
>>>>
>>>> Stacksize 0 -> default stack size : ok
>>>> Stacksize > 0 and <=3D 16911 : Segmentation fault
>>>> Stacksize >=3D 16912 : ok
>>>>
>>>> Any hints ?
>>> What does the task do? If it uses printf, printf needs a lot of room =
on
>>> the stack.
>>>
>>
>> To clarify:
>> It does not depend on the task body, the task is not even started.
>> The segfault happens when calling rt_task_create(), before rt_task_sta=
rt()
>> is called.
>=20
> Actually, when calling rt_task_create, the thread is created, under the=

> hood, and waits to be started. So the segmentation fault is most
> certainly due to a stack overflow in the newly created thread.
>=20
> And I am afraid I know why it happens: the newly merged user-space
> signals support requires roughly 16 * sizeof(struct siginfo) on stack.
> But this amounts to two Kbytes here. Could you run the following progra=
m
> on your target ?
>=20
> #include <stdio.h>
> #include <signal.h>
>=20
> struct xnsig {
>         unsigned nsigs;
>         unsigned remaining;
>         struct {
>                 unsigned muxid;
>                 struct siginfo si;
>         } pending[16];
> };
>=20
> int main(void)
> {
>         printf("%u\n", sizeof(struct xnsig));
>         return 0;
> }
>=20

output=3D2120
my system: debian lenny, linux 2.6.32.2, xenomai 2.5.0

kisda


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