From mboxrd@z Thu Jan  1 00:00:00 1970
From: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Subject: Re: [PATCH v3 2/4] ethdev: move error checking macros to
 header
Date: Tue, 10 Nov 2015 17:08:06 +0100
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On Mon, Nov 09, 2015 at 02:02:28PM +0000, Richardson, Bruce wrote:
[...]
> > From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
[...]
> > Untested but I guess modifying that function accordingly would look like:
> > 
> >  static inline void
> >  rte_pmd_debug_trace(const char *func_name, const char *fmt, ...)
> >  {
> >          va_list ap;
> >          va_start(ap, fmt);
> > 
> >          static __thread char buffer[vsnprintf(NULL, 0, fmt, ap)];
> > 
> >          va_end(ap);
> > 	 va_start(ap, fmt);
> >          vsnprintf(buffer, sizeof(buffer), fmt, ap);
> > 	 va_end(ap);
> >          rte_log(RTE_LOG_ERR, RTE_LOGTYPE_PMD, "%s: %s", func_name,
> > buffer);
> >  }
> > 
> 
> Looks a much better option.
> 
> From this, though, I assume then that we are only looking to support the -pedantic flag in conjuction with c99 mode or above. Supporting -pedantic with the pre-gcc-5 versions won't allow that to work though, as variably sized arrays only came in with c99, and were gnu extensions before that.

Right, -pedantic must follow a given standard such as -std=gnu99 otherwise
it's meaningless.

However pre-GCC 5 is fine for most if not all features we use, see:

 https://gcc.gnu.org/c99status.html

Mixed code and declarations are supported since GCC 3.0, __VA_ARGS__ in
macros since GCC 2.95 and variable length arrays since GCC 0.9, so as long
as we use a version that implements -std=gnu99 (or -std=c99 to be really
pedantic), it's fine.

Besides DPDK already uses C99 extensively, even a few C11 features (such as
embedded anonymous struct definitions) currently supported in C99 mode as
compiler extensions. I think we can safely ignore compilers that don't
support common C99 features.

-- 
Adrien Mazarguil
6WIND