Re: [Patch] ARM define atomic_exchange_acq/atomic_exchange_rel to __atomic_exchange_n

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Mon, 2 Sep 2013, Dinar Temirbulatov wrote:

> Hi,
> Another version of change, I added
> atomic_compare_and_exchange_val_acq/atomic_compare_and_exchange_val_rel
> and atomic_compare_and_exchange_bool_acq/atomic_compare_and_exchange_boot_rel
> defenitions and also for gcc-4.7 and higher in the case of unsupported
> atomic compare and swap operation, it uses the kernel helper inlines.
> Tested on arm a9 with no new regressions. Ok to commit?
> Oh, sorry. I missed to attach the change. Here it is.

For subsequent patch revisions, please note there should be an extra space 
after "#" for preprocessor directives inside #if conditionals, one per 
level of #if nesting (other than toplevel multiple-inclusion guards) - 
which means that if conditioning existing code, you need to adjust 
directives inside that code.

This patch appears to have too much duplication.  For example, you 
duplicate the definition of __arm_assisted_compare_and_exchange_val_32_acq 
- but that should not need any extra conditionals at all (beyond the 
existing #ifndef __arm_assisted_compare_and_exchange_val_32_acq), there's 
no reason ever not to define it.  Similarly, you duplicate 
__arch_compare_and_exchange_val_64_acq, but with proper #if structure 
there should only need to be one copy of the version that uses 
__arm_link_error.

What I think you should aim for is that each definition, or small group of 
definitions, uses conditionals in the form

#if __GNUC_PREREQ (4, 7) && defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
/* Version using __atomic_*.  */
#elif defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
/* Version using __sync_*.  */
#else
/* Version using __arm_assisted_*.  */
#endif

with cases omitted if not useful for that particular macro (this may 
include some macros not being defined at all in some cases).  So don't 
insert any global conditionals affecting all the existing definitions at 
all - look at each block of conditionals and add a third case as needed, 
along with any new macros (again with conditionals in that form) that are 
appropriate.

Where you use abort () in some definitions, use __arm_link_error () 
instead, like for the existing definitions.

-- 
Joseph S. Myers
joseph@codesourcery.com