On Fri, Apr 17, 2015 at 08:17:26PM +0200, Jan Kiszka wrote:
> On 2015-04-17 20:12, Gilles Chanteperdrix wrote:
> > On Fri, Apr 17, 2015 at 08:10:40PM +0200, Jan Kiszka wrote:
> >> On 2015-04-17 20:08, Gilles Chanteperdrix wrote:
> >>> On Fri, Apr 17, 2015 at 08:05:57PM +0200, Jan Kiszka wrote:
> >>>> On 2015-04-17 19:50, Gilles Chanteperdrix wrote:
> >>>>> On Fri, Apr 17, 2015 at 07:34:30PM +0200, Jan Kiszka wrote:
> >>>>>> Hi,
> >>>>>>
> >>>>>> analyzing page faults of an application that prefers to set its own
> >>>>>> stacks, I noticed a problem in Xenomai (2 and 3), at least from the
> >>>>>> usability POV: We document the minimum stack stack as PTHREAD_STACK_MIN
> >>>>>> + 1 page, at least in Xenomai 3, and we enforce that on thread
> >>>>>> creation.
> >>>>>> However, enforcement is doomed to fail if the stack is preallocated
> >>>>>> (and
> >>>>>> that too small).
> >>>>>>
> >>>>>> As we cannot detect if the user set a stack address in pthread_attr_t,
> >>>>>> I
> >>>>>> would suggest to fail thread creation instead of performing it with
> >>>>>> improper parameters. Other suggestions? If not, I would prepare a patch
> >>>>>> for Xenomai 3 (for 2 only if desired).
> >>>>>
> >>>>> It seems to me we can detect the parameters in the pthread_attr_t
> >>>>> using pthread_attr_getstack. So, we can get __wrap_pthread_create to
> >>>>> fail if the size is not sufficient.
> >>>>
> >>>> Nope, unfortunately not:
> >>>>
> >>>> "If the pthread_attr_getstack() function is called before the stackaddr
> >>>> attribute has been set, the behavior is unspecified."
> >>>
> >>> It is unspecified by POSIX, but Xenomai supports only two
> >>> implementations, glibc and uClibc, so, we can look at what these two
> >>> libraries do. I would bet they return you a NULL stack pointer or
> >>> something.
> >>
> >> I would have expected that, too, but the results for glibc seem random.
> >> Plus there is the risk that something changes, thus we become
> >> version-dependent.
> >
> > Ok then, what about the influence of pthread_attr_setstack() on
> > pthread_attr_getstacksize(), maybe more luck there?
>
> setstack defines the size getstacksize returns. So does setstacksize.
>
> What happens during setstacksize is apparently that the address is set
> to NULL - size. But, again, that is just the current glibc behaviour.
Yes, ok, but in order to test the stack size passed by the user, it
simply means we can use getstacksize and bail out if not sufficient.
--
Gilles.
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