Re: [PATCH] rcu: remove VLAs

[Andre Muezerie <andremue@linux.microsoft.com>]

On Fri, May 16, 2025 at 11:22:05AM +0200, David Marchand wrote:
> Andre,
> 
> On Fri, Mar 7, 2025 at 2:40 AM Andre Muezerie
> <andremue@linux.microsoft.com> wrote:
> >
> > There are two lines that were using VLAs, which are not supported by
> > MSVC.
> >
> > 1)
> > ../lib/rcu/rte_rcu_qsbr.c:326:12: warning: variable length array used [-Wvla]
> >   326 |         char data[dq->esize];
> >       |                   ^~~~~~~~~
> > 2)
> > ../lib/rcu/rte_rcu_qsbr.c:389:12: warning: variable length array used [-Wvla]
> >   389 |         char data[dq->esize];
> >       |                   ^~~~~~~~~
> >
> > The short-term fix is to use alloca, to allow progress with the msvc
> > compatibility work.
> > The long-term plan involves API changes and therefore can only be applied
> > with a new release. This long-term plan consists of introducing some
> > reasonable limitation on RCU DQ element size.
> >
> > Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> 
> Afaiu, enabling RCU with MSVC depends on this current patch and a fix
> in test/ipfrag:
> https://patchwork.dpdk.org/project/dpdk/patch/1741313581-14300-1-git-send-email-andremue@linux.microsoft.com/.
> Is there anything else missing?
> 
> If not, then I would be for doing this enabling as part of this
> current patch (I can do this when applying).
> WDYT?
> 

You're correct. When enabling RCU lib, test_ipfrag is build and fails if the mentioned
patch is not applied yet. If you apply that patch first, it would be great if you
could enable RCU on Windows as part of this patch. Nothing else should be missing.

I had not enabled it before to not break the CI build.

> 
> -- 
> David Marchand