Re: [Qemu-devel] [PATCH v2] nbd: fix uninitialized variable warning

[Eric Blake <eblake@redhat.com>]

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On 7/16/19 5:07 AM, Marc-André Lureau wrote:
> ../block/nbd.c: In function 'nbd_co_request':
> ../block/nbd.c:745:8: error: 'local_reply.type' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>      if (chunk->type == NBD_REPLY_TYPE_NONE) {
>         ^
> ../block/nbd.c:710:14: note: 'local_reply.type' was declared here
>      NBDReply local_reply;
>               ^~~~~~~~~~~
> ../block/nbd.c:710:14: error: 'local_reply.flags' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> ../block/nbd.c:738:8: error: 'local_reply.<U4be0>.magic' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>      if (nbd_reply_is_simple(reply) || s->quit) {
>         ^
> ../block/nbd.c:710:14: note: 'local_reply.<U4be0>.magic' was declared here
>      NBDReply local_reply;
>               ^~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> Reported-by: Thomas Huth <thuth@redhat.com>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  block/nbd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Actually, since this patch didn't fix all the cases of use of an uninit
variable, I'm wondering if this one-liner would be a better patch for
the issue (that is, fix it so that nbd_co_receive_one_chunk never leaves
reply uninit, rather than chasing down which callers might need init),
and with a perk of not relying on a gcc extension:

diff --git i/block/nbd.c w/block/nbd.c
index 8d565cc624ec..f751a8e633e5 100644
--- i/block/nbd.c
+++ w/block/nbd.c
@@ -640,6 +640,7 @@ static coroutine_fn int nbd_co_receive_one_chunk(
                                           request_ret, qiov, payload,
errp);

     if (ret < 0) {
+        memset(reply, 0, sizeof *reply);
         s->quit = true;
     } else {
         /* For assert at loop start in nbd_connection_entry */

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org


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