Re: general protection faults with "git grep" version 1.7.7.1

From: Jim Meyering <jim@meyering.net>
Date: Oct 25, 2011, 20:24 UTC
Message-ID: <87zkgoakfr.fsf@rho.meyering.net>
In-Reply-To: <201110251854.43369.trast@student.ethz.ch>

Thomas Rast wrote: ...

Show 21 quoted lines

>> The real problem seems to be in glibc, with its addition of
>> the "leaf" attribute to those synchronization primitives:
>>
>>   http://bugzilla.redhat.com/747377#c22
>
> Aha.  Glad you found it :-)
>
> Meanwhile I read
>
>   http://www.hpl.hp.com/techreports/2004/HPL-2004-209.html
>
> which discusses a similar issue in section 4.3, but is very
> interesting on its own.  It's funny how it says
>
>   We know of at least three optimizing compilers (two of them
>   production compilers) that performed this transformation at some
>   point during their lifetime; usually at least partially reversing
>   the decision when the implications on multi-threaded code became
>   known.
>
> I guess that would be four now if it was literally the same problem.

Yep. For those not following the BZ comments at the about URL, POSIX is quite clear. Quoting from http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_11:

    The following functions synchronize memory with respect to other threads:

        fork
        pthread_barrier_wait
        pthread_cond_broadcast
        pthread_cond_signal
        pthread_cond_timedwait
        pthread_cond_wait
        pthread_create
        pthread_join
        pthread_mutex_lock
        pthread_mutex_timedlock
        pthread_mutex_trylock
        pthread_mutex_unlock
        pthread_spin_lock
        pthread_spin_trylock
        pthread_spin_unlock
        pthread_rwlock_rdlock
        pthread_rwlock_timedrdlock
        pthread_rwlock_timedwrlock
        pthread_rwlock_tryrdlock
        pthread_rwlock_trywrlock
        pthread_rwlock_unlock
        pthread_rwlock_wrlock
        sem_post
        sem_timedwait
        sem_trywait
        sem_wait
        semctl
        semop
        wait
        waitpid

glibc's addition of the leaf attribute to any of those appears to make gcc violate that.