Re: [PATCH v2] eal: introduce atomics abstraction

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

On Thu, Feb 09, 2023 at 09:04:16AM +0000, 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?

there is code using posix extensions, there are two ways to use them
without emitting warnings.

1. -std=gnu11 (to get C11 with GNU extensions)

-- or --

2. -std=c11 and then in the source files consuming the C11 GNU
extensions do some dance with various GNUC macros before including
various stdxxx.h headers to enable the extensions for the translation
unit.

i vaguely recall that if you try to do a test build with -std=c11 over
the whole tree with meson --werror it will highlight the exact code i'm
talking about.

selfishly i'd be happy to see (2) done and potentially eliminate the use
of the extensions, but i didn't want to be disruptive as a part of this
change.

> 
> /Bruce