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 08.01.2010 12:57, schrieb Gilles Chanteperdrix:
> Stefan Kisdaroczi wrote:
>> 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.
> 
> PTHREAD_STACK_MIN varies a lot depending on architectures and even
> depending on the glibc versions. Which is why we took 32 Kb as the
> default stack size. Since the default is enough even for struct xnsig,
> if you are asking a smaller size, you may have good reasons to do so. We
> should check that the size is at least sizeof(struct xnsig), but since
> PTHREAD_STACK_MIN is larger than struct xnsig, it should work as is.
> 
> The point is that your system seems to require 16 Kb whereas
> sizeof(struct xnsig) is only 2Kb. So, there is something wrong somewhere
> else.
> 
> Could you run the segfaulting program inside gdb, and print the frames
> infos ?

gdb logfile attached

kisda

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Starting program: /home/ski/src/xenotest/trivial-periodic 
[Thread debugging using libthread_db enabled]
[New Thread 0xb75ba6c0 (LWP 21336)]
[New Thread 0xb75b9b90 (LWP 21339)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb75b9b90 (LWP 21339)]
0xb7753783 in ?? () from /lib/ld-linux.so.2
#0  0xb7753783 in ?? () from /lib/ld-linux.so.2
#1  0xb77592e0 in ?? () from /lib/ld-linux.so.2
#2  0xb771f7fd in xeno_sigwinch_handler () from /usr/lib/libnative.so.3
#3  0xb771f8a6 in xeno_sigshadow_handler () from /usr/lib/libnative.so.3
#4  <signal handler called>
#5  0xb771e1e0 in ?? () from /usr/lib/libnative.so.3
#6  0xb75b93b8 in ?? ()
#7  0xb7721208 in ?? () from /usr/lib/libnative.so.3
#8  0xb77213c0 in ?? () from /usr/lib/libnative.so.3
#9  0xb771f700 in ?? () from /usr/lib/libnative.so.3
#10 0x00000000 in ?? ()
Stack frame at 0xb75b7008:
 eip = 0xb7753783; saved eip 0xb77592e0
 called by frame at 0xb75b7020
 Arglist at 0xb75b6ffc, args: 
 Locals at 0xb75b6ffc, Previous frame's sp is 0xb75b7008
 Saved registers:
  ebp at 0xb75b7000, eip at 0xb75b7004
Stack frame at 0xb75b7020:
 eip = 0xb77592e0; saved eip 0xb771f7fd
 called by frame at 0xb75b78a0, caller of frame at 0xb75b7008
 Arglist at 0xb75b7004, args: 
 Locals at 0xb75b7004, Previous frame's sp is 0xb75b7020
 Saved registers:
  eip at 0xb75b701c
Stack frame at 0xb75b78a0:
 eip = 0xb771f7fd in xeno_sigwinch_handler; saved eip 0xb771f8a6
 called by frame at 0xb75b7950, caller of frame at 0xb75b7020
 Arglist at 0xb75b7898, args: 
 Locals at 0xb75b7898, Previous frame's sp is 0xb75b78a0
 Saved registers:
  ebp at 0xb75b7898, eip at 0xb75b789c
Stack frame at 0xb75b7950:
 eip = 0xb771f8a6 in xeno_sigshadow_handler; saved eip 0xb774540c
 called by frame at 0xb75b7a58, caller of frame at 0xb75b78a0
 Arglist at 0xb75b7948, args: 
 Locals at 0xb75b7948, Previous frame's sp is 0xb75b7950
 Saved registers:
  ebp at 0xb75b7948, eip at 0xb75b794c
Stack frame at 0xb75b7a58:
 eip = 0xb774540c in __kernel_rt_sigreturn; saved eip 0xb771e1e0
 called by frame at 0xb75b7a5c, caller of frame at 0xb75b7950
 Arglist at unknown address.
 Locals at unknown address, Previous frame's sp is 0xb75b7a58
 Saved registers:
  eax at 0xb75b7a1c, ecx at 0xb75b7a18, edx at 0xb75b7a14, ebx at 0xb75b7a10,
  ebp at 0xb75b7a08, esi at 0xb75b7a04, edi at 0xb75b7a00, eip at 0xb75b7a28
Stack frame at 0xb75b7a5c:
 eip = 0xb771e1e0; saved eip 0xb75b93b8
 called by frame at 0xb75b7a60, caller of frame at 0xb75b7a58
 Arglist at 0xb75b7a54, args: 
 Locals at 0xb75b7a54, Previous frame's sp is 0xb75b7a5c
 Saved registers:
  eip at 0xb75b7a58
Stack frame at 0xb75b7a60:
 eip = 0xb75b93b8; saved eip 0xb7721208
 called by frame at 0xb75b7a64, caller of frame at 0xb75b7a5c
 Arglist at 0xb75b7a58, args: 
 Locals at 0xb75b7a58, Previous frame's sp is 0xb75b7a60
 Saved registers:
  eip at 0xb75b7a5c
Stack frame at 0xb75b7a64:
 eip = 0xb7721208; saved eip 0xb77213c0
 called by frame at 0xb75b7a68, caller of frame at 0xb75b7a60
 Arglist at 0xb75b7a5c, args: 
 Locals at 0xb75b7a5c, Previous frame's sp is 0xb75b7a64
 Saved registers:
  eip at 0xb75b7a60
Stack frame at 0xb75b7a68:
 eip = 0xb77213c0 in xeno_sigshadow_installed; saved eip 0xb771f700
 called by frame at 0xb75b7a6c, caller of frame at 0xb75b7a64
 Arglist at 0xb75b7a60, args: 
 Locals at 0xb75b7a60, Previous frame's sp is 0xb75b7a68
 Saved registers:
  eip at 0xb75b7a64
Stack frame at 0xb75b7a6c:
 eip = 0xb771f700 in xeno_sigshadow_install; saved eip 0x0
 called by frame at 0xb75b7a70, caller of frame at 0xb75b7a68
 Arglist at 0xb75b7a64, args: 
 Locals at 0xb75b7a64, Previous frame's sp is 0xb75b7a6c
 Saved registers:
  eip at 0xb75b7a68
Stack frame at 0xb75b7a70:
 eip = 0x0; saved eip 0x0
 caller of frame at 0xb75b7a6c
 Arglist at 0xb75b7a68, args: 
 Locals at 0xb75b7a68, Previous frame's sp is 0xb75b7a70
 Saved registers:
  eip at 0xb75b7a6c
The program is running.  Exit anyway? (y or n) 

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