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Re: Static TLS size and stack size


Siddhesh Poyarekar <siddhesh@redhat.com> writes:

> On Tue, 05 Jun 2012 06:28:00 -0700, Ian wrote:
>
>> If I set the desired stack size via pthread_attr_setstacksize in a
>> pthread_attr_t passed to pthread_create, I don't get a stack of that
>> size.  The guard page is subtracted from the stack size.  More
>> importantly, the static TLS size is subtracted.  If the result is
>> negative, pthread_create returns an EINVAL error.  If the result is
>> non-negative, I can wind up a stack much smaller than requested.
>> 
>> This is a problem for the Go library.  The Go library uses GCC's
>> -fsplit-stack support, so when creating a thread it asks for a stack
>> size of PTHREAD_STACK_MIN.  If the Go library is used by a program
>> with a large number of TLS variables, or a large TLS array, I can
>> wind up with an unexpected failure, or with a segmentation violation
>> as the small stack is overrun.
>> 
>> I tried working around this by calling the glibc-private function
>> _dl_get_static_tls_info, but, besides being highly nonportable, Jakub
>> informs me that that will cause rpm to refuse to build a gcc RPM.
>> 
>> I don't see a good way to handle this.  To me it simply seems like a
>> bug that glibc takes the static TLS size out of the requested stack
>> size. Why not increase the requested stack size instead?
>> 
>> Any suggestions for what I can do here?
>
> This is a known issue in glibc that is being worked on. See:
>
> http://sourceware.org/bugzilla/show_bug.cgi?id=11787


Thanks for the pointer.

Does anybody have any suggestions for how to deal with the problem when
using current libc implementations?

Ian


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