RE: [PATCH] acl: fix build with GCC 15 on aarch64

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Thursday, March 27, 2025 10:37 AM
> To: Bruce Richardson <bruce.richardson@intel.com>
> Cc: dev@dpdk.org; bluca@debian.org; stable@dpdk.org; Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>; David Christensen
> <drc@linux.ibm.com>; Wathsala Vithanage <wathsala.vithanage@arm.com>
> Subject: Re: [PATCH] acl: fix build with GCC 15 on aarch64
> 
> On Thu, Mar 27, 2025 at 9:55 AM Bruce Richardson
> <bruce.richardson@intel.com> wrote:
> >
> > On Wed, Mar 26, 2025 at 11:39:28AM +0100, David Marchand wrote:
> > > Caught in OBS for Fedora Rawhide on aarch64:
> > >
> > > [  198s] In file included from ../lib/acl/acl_run_neon.h:7,
> > > [  198s]                  from ../lib/acl/acl_run_neon.c:5:
> > > [  198s] In function ‘alloc_completion’,
> > > [  198s]     inlined from ‘acl_start_next_trie’ at
> > >       ../lib/acl/acl_run.h:140:24,
> > > [  198s]     inlined from ‘search_neon_4.isra’ at
> > >       ../lib/acl/acl_run_neon.h:239:20:
> > > [  198s] ../lib/acl/acl_run.h:93:25: error: ‘cmplt’ may be used
> > >       uninitialized [-Werror=maybe-uninitialized]
> > > [  198s]    93 |                 if (p[n].count == 0) {
> > > [  198s]       |                     ~~~~^~~~~~
> > > [  198s] ../lib/acl/acl_run_neon.h: In function ‘search_neon_4.isra’:
> > > [  198s] ../lib/acl/acl_run_neon.h:230:27: note: ‘cmplt’ declared here
> > > [  198s]   230 |         struct completion cmplt[4];
> > > [  198s]       |                           ^~~~~
> > >
> > > The code was resetting sequentially cmpl[].count at the exact index that
> > > later call to alloc_completion uses.
> > > While this code seems correct, GCC 15 does not understand this (probably
> > > when applying some optimisations).
> > >
> > > Instead, reset cmpl[].count all at once in acl_set_flow, and cleanup the
> > > various vectorized implementations accordingly.
> > >
> > > Bugzilla ID: 1678
> > > Cc: stable@dpdk.org
> > >
> > > Signed-off-by: David Marchand <david.marchand@redhat.com>
> > > ---
> > >  lib/acl/acl_run.h         | 5 +++++
> > >  lib/acl/acl_run_altivec.h | 8 ++------
> > >  lib/acl/acl_run_avx2.h    | 4 +---
> > >  lib/acl/acl_run_neon.h    | 8 ++------
> > >  lib/acl/acl_run_scalar.c  | 4 +---
> > >  lib/acl/acl_run_sse.h     | 8 ++------
> > >  6 files changed, 13 insertions(+), 24 deletions(-)
> > >
> > > diff --git a/lib/acl/acl_run.h b/lib/acl/acl_run.h
> > > index 7f092413cd..9fd3e60021 100644
> > > --- a/lib/acl/acl_run.h
> > > +++ b/lib/acl/acl_run.h
> > > @@ -176,6 +176,8 @@ acl_set_flow(struct acl_flow_data *flows, struct completion *cmplt,
> > >       uint32_t cmplt_size, const uint8_t **data, uint32_t *results,
> > >       uint32_t data_num, uint32_t categories, const uint64_t *trans)
> > >  {
> > > +     unsigned int i;
> > > +
> > >       flows->num_packets = 0;
> > >       flows->started = 0;
> > >       flows->trie = 0;
> > > @@ -187,6 +189,9 @@ acl_set_flow(struct acl_flow_data *flows, struct completion *cmplt,
> > >       flows->data = data;
> > >       flows->results = results;
> > >       flows->trans = trans;
> > > +
> > > +     for (i = 0; i < cmplt_size; i++)
> > > +             cmplt[i].count = 0;
> > >  }
> >
> > Minor nit, but since we are using c11 standard, is it not better to declare
> > "i" inside the "for" statement. Keeps diffs simpler for adding/removing
> > code, I think.
> 
> I still have this (bad) habit but yes, it looks nicer with declaring
> in for() itself.

My vote would be to keep it in an old fashioned way.
Nothing is wrong in defining variable to use at the start of the function :)