netdev - Re: [PATCH bpf-next] samples/bpf: silence compiler warning for xdpsock

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Date:   Fri, 1 Mar 2019 15:10:07 -0800
From:   Song Liu <liu.song.a23@...il.com>
To:     Jonathan Lemon <jlemon@...gsvamp.com>
Cc:     Yonghong Song <yhs@...com>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, kernel-team@...com
Subject: Re: [PATCH bpf-next] samples/bpf: silence compiler warning for xdpsock_user.c

On Fri, Mar 1, 2019 at 11:10 AM Jonathan Lemon <jlemon@...gsvamp.com> wrote:
>
> On 28 Feb 2019, at 22:19, Yonghong Song wrote:
>
> > Compiling xdpsock_user.c with 4.8.5, I hit the following
> > compilation warning:
> >     HOSTCC  samples/bpf/xdpsock_user.o
> >   /data/users/yhs/work/net-next/samples/bpf/xdpsock_user.c: In
> > function ‘main’:
> >   /data/users/yhs/work/net-next/samples/bpf/xdpsock_user.c:449:6:
> > warning: ‘idx_cq’ may be used unini
> >   tialized in this function [-Wmaybe-uninitialized]
> >     u32 idx_cq, idx_fq;
> >         ^
> >   /data/users/yhs/work/net-next/samples/bpf/xdpsock_user.c:606:7:
> > warning: ‘idx_rx’ may be used unini
> >   tialized in this function [-Wmaybe-uninitialized]
> >      u32 idx_rx, idx_tx = 0;
> >          ^
> >   /data/users/yhs/work/net-next/samples/bpf/xdpsock_user.c:506:6:
> > warning: ‘idx_rx’ may be used unini
> >   tialized in this function [-Wmaybe-uninitialized]
> >     u32 idx_rx, idx_fq = 0;
> >
> > As an example, the code pattern looks like:
> >     u32 idx_cq;
> >     ...
> >     ret = xsk_ring_prod__reserve(&xsk->umem->fq, rcvd, &idx_fq);
> >     if (ret) {
> >       ...
> >     }
> >     ... idx_fq ...
> > The compiler warns since it does not know whether &idx_fq is assigned
> > or not inside the library function xsk_ring_prod__reserve().
> >
> > Let us assign an initial value 0 to such auto variables to silence
> > compiler warning.
> >
> > Fixes: 248c7f9c0e21 ("samples/bpf: convert xdpsock to use libbpf for
> > AF_XDP access")
> > Signed-off-by: Yonghong Song <yhs@...com>
> > ---
> >  samples/bpf/xdpsock_user.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
> > index 9c76d6d43deb..d08ee1ab7bb4 100644
> > --- a/samples/bpf/xdpsock_user.c
> > +++ b/samples/bpf/xdpsock_user.c
> > @@ -446,7 +446,7 @@ static void kick_tx(struct xsk_socket_info *xsk)
> >
> >  static inline void complete_tx_l2fwd(struct xsk_socket_info *xsk)
> >  {
> > -     u32 idx_cq, idx_fq;
> > +     u32 idx_cq = 0, idx_fq = 0;
> >       unsigned int rcvd;
> >       size_t ndescs;
> >
> > @@ -503,7 +503,7 @@ static inline void complete_tx_only(struct
> > xsk_socket_info *xsk)
> >  static void rx_drop(struct xsk_socket_info *xsk)
> >  {
> >       unsigned int rcvd, i;
> > -     u32 idx_rx, idx_fq = 0;
> > +     u32 idx_rx = 0, idx_fq = 0;
> >       int ret;
> >
> >       rcvd = xsk_ring_cons__peek(&xsk->rx, BATCH_SIZE, &idx_rx);
> > @@ -603,7 +603,7 @@ static void l2fwd(struct xsk_socket_info *xsk)
> >  {
> >       for (;;) {
> >               unsigned int rcvd, i;
> > -             u32 idx_rx, idx_tx = 0;
> > +             u32 idx_rx = 0, idx_tx = 0;
> >               int ret;
> >
> >               for (;;) {
> > --
> > 2.17.1
>
> Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>

Acked-by: Song Liu <songliubraving@...com>