Re: Compilation errors in drivers/event/opdl/

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

(Replying since you added me to this thread)

On Sun, Jan 21, 2018 at 06:49:13PM +0100, Thomas Monjalon wrote:
> 21/01/2018 18:34, Stephen Hemminger:
> > On Sat, 20 Jan 2018 09:44:46 +0100
> > Thomas Monjalon <thomas@monjalon.net> wrote:
> > 
> > > 20/01/2018 06:18, Patil, Harish:
> > > > Hi,
> > > > 
> > > > I am seeing below compilation errors in drivers/event/opdl/, this is with
> > > > cloned latest DPDK (git clone http://dpdk.org/git/dpdk).
> > > > 
> > > > ..
> > > > ..
> > > > /home2/hpatil/e4/jan19-inbox-submit/dpdk/drivers/event/opdl/opdl_evdev_xsta
> > > > ts.c: In function ‘opdl_xstats_get_names’:
> > > > /home2/hpatil/e4/jan19-inbox-submit/dpdk/drivers/event/opdl/opdl_evdev_xsta
> > > > ts.c:89:2: error: ‘for’ loop initial declarations are only allowed in
> > > > C99 mode
> > > >   for (uint32_t j = 0; j < max_num_port_xstat; j++) {
> > > >   ^  
> > > 
> > > My compiler does not raise this error.
> > > What is your compiler?
> > > 
> > > Anyone to fix it QUICKLY please? today?
> > > 
> > > Harish, do you think we should revert if not fixed?
> > 
> > Using declaration in for loop is a C++ thing which was inherited into C99.
> > Does DPDK require C99 mode?
> 
> No DPDK is not generally C99.

Except we use enough C99isms (named initializers anyone?) that I think it's
safe to say DPDK won't ever compile in C90 mode.

> 
> > Putting loop variables in for() looks better, but the rest of DPDK
> > doesn't use that style.
> 
> C99 was forced for this driver as a quick fix.
> 
> Either the coding style guideline is updated to C99,
> or this driver must be adapted to the DPDK coding style.
> I have no strong opinion.

When -std is not specified, depending on its version GCC defaults either to
gnu90, gnu99 or gnu11, all based on the C standard in question with a number
of GNU extensions.

Named initializers typically never fail because they're otherwise part of
the GNU extensions. Others such as the "for" declaration above apparently
aren't considered part of gnu90.

> Is C99 well supported in all compilers we want to use (including Windows)?

If by Windows you mean MSVC, from memory (likely outdated) it's actually a
C++ compiler that only provides limited support for C99, this fact will
trigger many other issues. The above loop won't be one of them though.

On the GCC/clang side, -std=gnu99 is what we assume in DPDK today without
explicitly documenting it. Exported headers conform a stricter standard,
they are compatible with -std=c99 with GNU extensions explicitly tagged
whenever they can't be worked around.

-- 
Adrien Mazarguil
6WIND