Re: [PATCH v4 6/6] devtools: forbid new direct use of GCC atomic builtins

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Thu, Aug 17, 2023 at 01:57:01PM +0200, Morten Brørup wrote:
> > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> > Sent: Wednesday, 16 August 2023 23.39
> > 
> > Refrain from using compiler __atomic_xxx builtins DPDK now requires
> > the use of rte_atomic_<op>_explicit macros when operating on DPDK
> > atomic variables.
> 
> There is probably no end to how much can be added to checkpatches.
> 
> You got the important stuff, so below are only further suggestions!
> 
> [...]
> 
> > -	# refrain from using compiler __atomic_{add,and,nand,or,sub,xor}_fetch()
> > +	# refrain from using compiler __atomic_xxx builtins
> >  	awk -v FOLDERS="lib drivers app examples" \
> > -		-v EXPRESSIONS="__atomic_(add|and|nand|or|sub|xor)_fetch\\\(" \
> > +		-v EXPRESSIONS="__atomic_.*\\\(" \
> >  		-v RET_ON_FAIL=1 \
> > -		-v MESSAGE='Using __atomic_op_fetch, prefer __atomic_fetch_op' \
> > +		-v MESSAGE='Using __atomic_xxx builtins' \
> 
> Alternatively:
> 		-v MESSAGE='Using __atomic_xxx built-ins, prefer rte_atomic_xxx' \

i can adjust the wording as you suggest, no problem

> 
> >  		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \
> >  		"$1" || res=1
> > 
> > --
> > 1.8.3.1
> 
> This could be updated too:
> 
> 	# refrain from using compiler __atomic_thread_fence()
> 	# It should be avoided on x86 for SMP case.
> 	awk -v FOLDERS="lib drivers app examples" \
> 		-v EXPRESSIONS="__atomic_thread_fence\\\(" \
> 		-v RET_ON_FAIL=1 \
> -		-v MESSAGE='Using __atomic_thread_fence' \
> +		-v MESSAGE='Using __atomic_thread_fence built-in, prefer __rte_atomic_thread_fence' \
> 		-f $(dirname $(readlink -f $0))/check-forbidden-tokens.awk \

yeah, i left this one separate i think the advice is actually use
rte_atomic_thread_fence which may be an inline function that uses
__rte_atomic_thread_fence

> 		"$1" || res=1
> 
> You could also add C11 variants of these tests...
> atomic_(load|store|exchange|compare_exchange_(strong|weak)|fetch_(add|sub|and|xor|or|nand)|flag_(test_and_set|clear))[_explicit], and
> atomic_thread_fence.
> 
> And a test for using "_Atomic".

direct use would cause early compilation in the CI so it would be caught
fairly early. i'm not sure i want to get into the business of trying to
add redundant (albiet cheaper) earlier checks.

though if there is a general call for this from the reviewers i'll add
them.

> 
> -Morten