Re: [Xenomai-help] native skin 2.5.0: rt_task_create() segfaults if stacksize parameter too small

[Stefan Kisdaroczi <kisda@domain.hid>]

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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 segfaults 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 with 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 <= 16911 : Segmentation fault
>>>> Stacksize >= 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_start()
>> is called.
> 
> 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.
> 
> 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 program
> on your target ?

salut gilles,

as the stacksize is already checked and increased to PTHREAD_STACK_MIN if
the value is too small, i suggest to take the stacksize needed by xenomai
into account too. The attached patch is clearly wrong, but it solved the
problem for me.

kisda

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--- xenomai-2.5.0.orig/src/skins/native/task.c
+++ xenomai-2.5.0/src/skins/native/task.c
@@ -148,9 +148,9 @@
 
 	if (!stksize)
 		stksize = 32 * 1024;
-	if (stksize < PTHREAD_STACK_MIN)
-		stksize = PTHREAD_STACK_MIN;
-
+	if (stksize < (PTHREAD_STACK_MIN + sizeof(struct xnsig)))
+		stksize = PTHREAD_STACK_MIN + sizeof(struct xnsig);
+	
 	pthread_attr_setinheritsched(&thattr, PTHREAD_EXPLICIT_SCHED);
 	memset(&param, 0, sizeof(param));
 	if (prio > 0) {

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