netdev - [PATCH v2 bpf 11/11] samples/bpf: xdpsock: fix -Wmaybe-uninitialized

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Date:   Thu, 21 Apr 2022 00:39:57 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Alexander Lobakin <alobakin@...me>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Song Liu <songliubraving@...com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 bpf 11/11] samples/bpf: xdpsock: fix -Wmaybe-uninitialized

Fix two sort-of-false-positives in the xdpsock userspace part:

samples/bpf/xdpsock_user.c: In function 'main':
samples/bpf/xdpsock_user.c:1531:47: warning: 'tv_usec' may be used uninitialized in this function [-Wmaybe-uninitialized]
 1531 |                         pktgen_hdr->tv_usec = htonl(tv_usec);
      |                                               ^~~~~~~~~~~~~~
samples/bpf/xdpsock_user.c:1500:26: note: 'tv_usec' was declared here
 1500 |         u32 idx, tv_sec, tv_usec;
      |                          ^~~~~~~
samples/bpf/xdpsock_user.c:1530:46: warning: 'tv_sec' may be used uninitialized in this function [-Wmaybe-uninitialized]
 1530 |                         pktgen_hdr->tv_sec = htonl(tv_sec);
      |                                              ^~~~~~~~~~~~~
samples/bpf/xdpsock_user.c:1500:18: note: 'tv_sec' was declared here
 1500 |         u32 idx, tv_sec, tv_usec;
      |                  ^~~~~~

Both variables are always initialized when @opt_tstamp == true and
they're being used also only when @opt_tstamp == true. However, that
variable comes from the BSS and is being toggled from another
function. They can't be executed simultaneously to actually trigger
undefined behaviour, but purely technically it is a correct warning.
Just initialize them with zeroes.

Fixes: eb68db45b747 ("samples/bpf: xdpsock: Add timestamp for Tx-only operation")
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Acked-by: Song Liu <songliubraving@...com>
Signed-off-by: Alexander Lobakin <alobakin@...me>
---
 samples/bpf/xdpsock_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
index 9747d47a0a8f..a6d8291c8b38 100644
--- a/samples/bpf/xdpsock_user.c
+++ b/samples/bpf/xdpsock_user.c
@@ -1497,7 +1497,7 @@ static void rx_drop_all(void)
 static int tx_only(struct xsk_socket_info *xsk, u32 *frame_nb,
 		   int batch_size, unsigned long tx_ns)
 {
-	u32 idx, tv_sec, tv_usec;
+	u32 idx, tv_sec = 0, tv_usec = 0;
 	unsigned int i;

 	while (xsk_ring_prod__reserve(&xsk->tx, batch_size, &idx) <
--
2.36.0