Re: [PATCH v5] build: update DPDK to use C11 standard

[Bruce Richardson <bruce.richardson@intel.com>]

On Thu, Aug 10, 2023 at 07:48:39AM -0700, Stephen Hemminger wrote:
> On Thu, 10 Aug 2023 15:34:43 +0200
> Thomas Monjalon <thomas@monjalon.net> wrote:
> 
> > 03/08/2023 15:36, David Marchand:
> > > On Wed, Aug 2, 2023 at 2:32 PM Bruce Richardson
> > > <bruce.richardson@intel.com> wrote:  
> > > >
> > > > As previously announced, DPDK 23.11 will require a C11 supporting
> > > > compiler and will use the C11 standard in all builds.
> > > >
> > > > Forcing use of the C standard, rather than the standard with
> > > > GNU extensions, means that some posix definitions which are not in
> > > > the C standard are unavailable by default. We fix this by ensuring
> > > > the correct defines or cflags are passed to the components that
> > > > need them.
> > > >
> > > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > > Acked-by: Morten Brørup <mb@smartsharesystems.com>
> > > > Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>  
> > > Tested-by: Ali Alnubani <alialnu@nvidia.com>
> > > 
> > > The CI results look good.
> > > 
> > > Applied, thanks!  
> > 
> > The compiler support is updated, that's fine.
> > Should we go further and document some major Linux distributions?
> > One concern is to make clear RHEL 7 is not supported anymore.
> > Should it be a release note?
> > 

Well, DPDK currently is still building fine on Centos 7 for me, so let's
hold off on claiming anything until it's definitely broken.

> > 
> 
> Should be addressed in linux/sys_reqs.rst as well as deprecation notice.
> Also, is it possible to add automated check in build for compiler version?

I'd be a little careful about what we claim, and I think current docs are
accurate vs our original plans. What we didn't plan to support was the GCC
and Clang compiler versions in RHEL 7, but if one installs an updated GCC,
for example, the build should be fine on RHEL 7.

Now, though, we are having to re-evaluate our use of stdatomics, which
means we may not actually break RHEL 7 compatibility after all. We'll have
to "watch this space" as the saying goes!

Overall, I think the approach of build-time checks is the best, but not
for specific versions, but instead for capabilities. If/when we add support
for stdatomics to DPDK builds on Linux/BSD, at that point we put in the
initial compiler checks a suitable check for them being present and output
a suitable error if not found.

/Bruce