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

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Date:   Fri, 01 Mar 2019 09:17:40 -0800
From:   "Jonathan Lemon" <jlemon@...gsvamp.com>
To:     "Yonghong Song" <yhs@...com>
Cc:     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 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>