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[Bug nptl/15640] The ARM port of lll_unlock uses atomic compare and swap to release a lock
- From: "dtemirbulatov at gmail dot com" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Fri, 02 Aug 2013 17:55:59 +0000
- Subject: [Bug nptl/15640] The ARM port of lll_unlock uses atomic compare and swap to release a lock
- Auto-submitted: auto-generated
- References: <bug-15640-131 at http dot sourceware dot org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=15640
--- Comment #7 from Dinar Temirbulatov <dtemirbulatov at gmail dot com> ---
(In reply to Abhishek Deb from comment #6)
> Since the preprocessor macro atomic_exchange_rel was not explicity defined,
> it gets defined to atomic_compare_and_exhange_*, which is defined using
> gcc's atomic built-in __sync_val_compare_and_swap.
>
> But I think atomic exchange is not the same as atomic compare and exchange.
> An atomic exchange should be defined as ldex, stex, bne, whereas atomic
> compare and exchange is defined as ldex, cmp, bne, stex, bne.
>
> Doesn't look like gcc's atomic builtin in provides an explicit function to
> do that http://gcc.gnu.org/onlinedocs/gcc-4.6.2/gcc/Atomic-Builtins.html.
>
> However, gcc's atomic built in provides __sync_fetch_and_* . Can it be used
> to build an atomic exchange.
yes, All correct, except I think that it needs cmp after stex.
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