Re: [PATCH v2] eal: introduce atomics abstraction

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

On Thu, Feb 09, 2023 at 10:13:41PM +0000, Ferruh Yigit wrote:
> On 2/9/2023 5:40 PM, Tyler Retzlaff wrote:
> > On Thu, Feb 09, 2023 at 12:53:41PM +0000, Ferruh Yigit wrote:
> >> On 2/9/2023 9:04 AM, Bruce Richardson wrote:
> >>> On Wed, Feb 08, 2023 at 01:43:38PM -0800, Tyler Retzlaff wrote:
> >>>> Introduce atomics abstraction that permits optional use of standard C11
> >>>> atomics when meson is provided the new enable_stdatomics=true option.
> >>>>
> >>>> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> >>>> ---
> >>>>  config/meson.build                     | 11 ++++
> >>>>  lib/eal/arm/include/rte_atomic_32.h    |  6 ++-
> >>>>  lib/eal/arm/include/rte_atomic_64.h    |  6 ++-
> >>>>  lib/eal/include/generic/rte_atomic.h   | 96 +++++++++++++++++++++++++++++++++-
> >>>>  lib/eal/loongarch/include/rte_atomic.h |  6 ++-
> >>>>  lib/eal/ppc/include/rte_atomic.h       |  6 ++-
> >>>>  lib/eal/riscv/include/rte_atomic.h     |  6 ++-
> >>>>  lib/eal/x86/include/rte_atomic.h       |  8 ++-
> >>>>  meson_options.txt                      |  2 +
> >>>>  9 files changed, 139 insertions(+), 8 deletions(-)
> >>>>
> >>>> diff --git a/config/meson.build b/config/meson.build
> >>>> index 26f3168..25dd628 100644
> >>>> --- a/config/meson.build
> >>>> +++ b/config/meson.build
> >>>> @@ -255,6 +255,17 @@ endif
> >>>>  # add -include rte_config to cflags
> >>>>  add_project_arguments('-include', 'rte_config.h', language: 'c')
> >>>>  
> >>>> +stdc_atomics_enabled = get_option('enable_stdatomics')
> >>>> +dpdk_conf.set('RTE_STDC_ATOMICS', stdc_atomics_enabled)
> >>>> +
> >>>> +if stdc_atomics_enabled
> >>>> +if cc.get_id() == 'gcc' or cc.get_id() == 'clang'
> >>>> +    add_project_arguments('-std=gnu11', language: 'c')
> >>>
> >>> Is there a reason for using gnu11 on gcc and clang, rather than limiting
> >>> ourselves to proper c11 support?
> >>>
> >>
> >> +1 to stick to c11 standard instead of relying compiler extensions
> > 
> > the extensions are already in use. enabling -std=c11 causes warnings
> > about the extensions to start being emitted.
> > 
> 
> There is '__extension__' keyword (RTE_STD_C11) which is already used in
> many places, can it help to remove the warnings? If it helps we can use
> it, which helps to document where compiler extensions used in the code.

yeah, that macro name kind of makes no sense when you realize it expands
to __extension__ because a lot of places is it use isn't about an
extension for something from a standard header. sometimes it's used to
just annotate regular old gcc extensions/syntax.

i vaguely recall that the actual warning is for a missing declaration of
an extern function or something (presumably because it comes from glibc)
but not using -std=gnu11 or the macro dance didn't make the prototype
visible in the stdxxx.h header.

so i don't think __extension__ would actually be a good way to suppress
that warning and even if it did i'm trying to reduce code that carries
__extension__ to improve portability anyway.

i'll submit a new version of the patch series fixing it but without the
-std=gnu11 it's really the right thing to do.

ty

> 
> > but since i feel encouraged here, i think i will interpret your request
> > as let's limit the scope of enablement of extensions to where they are
> > already used instead of enabling them over the whole build.
> > 
> > i will submit a new revision patch to get rid of -std=gnu11 here.
> > 
> > thanks!