http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55561
--- Comment #29 from Dmitry Vyukov <dvyukov at google dot com> 2013-01-02
09:09:11 UTC ---
(In reply to comment #28)
> (In reply to comment #26)
> > For config/linux/ptrlock the changes are:
> > [...]
>
> Following your suggestions, I applied the following patch (mistakes are mine),
> which allows me to run without warnings from libgomp:
>
> Index: config/linux/wait.h
> ===================================================================
> --- config/linux/wait.h (revision 194730)
> +++ config/linux/wait.h (working copy)
> @@ -51,7 +51,7 @@
> if (__builtin_expect (gomp_managed_threads > gomp_available_cpus, 0))
> count = gomp_throttled_spin_count_var;
> for (i = 0; i < count; i++)
> - if (__builtin_expect (*addr != val, 0))
> + if (__builtin_expect (__atomic_load_n(addr,MEMMODEL_RELAXED) != val, 0))
> return 0;
> else
> cpu_relax ();
> Index: config/linux/ptrlock.c
> ===================================================================
> --- config/linux/ptrlock.c (revision 194730)
> +++ config/linux/ptrlock.c (working copy)
> @@ -50,9 +50,9 @@
> #endif
> do
> do_wait (intptr, 2);
> - while (*intptr == 2);
> + while (__atomic_load_n(intptr, MEMMODEL_RELAXED) == 2);
> __asm volatile ("" : : : "memory");
> - return *ptrlock;
> + return (void*)__atomic_load_n(ptrlock, MEMMODEL_ACQUIRE);
> }
>
> void
> Index: config/linux/ptrlock.h
> ===================================================================
> --- config/linux/ptrlock.h (revision 194730)
> +++ config/linux/ptrlock.h (working copy)
> @@ -48,8 +48,9 @@
> {
> uintptr_t oldval;
>
> - if ((uintptr_t) *ptrlock > 2)
> - return *ptrlock;
> + uintptr_t v = (uintptr_t)__atomic_load_n(ptrlock, MEMMODEL_ACQUIRE);
> + if (v > 2)
> + return (void*)v;
>
> oldval = 0;
> if (__atomic_compare_exchange_n (ptrlock, &oldval, 1, false,
Great!
Please post the patch to http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40362
I believe it is the correct fix for the bug.
