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

[Philippe Mathieu-Daudé]

Hi Marc-André,

On 7/16/19 10:42 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

Thomas reported this error when compiling with -O3 few months ago [1].
Are you using that, or the latest GCC emit a warning even with no -O3?

Personally I'd add:

Fixes: 86f8cdf3db8
Reported-by: Thomas Huth <address@hidden>

> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  block/nbd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/nbd.c b/block/nbd.c
> index 81edabbf35..02eef09728 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -707,7 +707,7 @@ static bool nbd_reply_chunk_iter_receive(BDRVNBDState *s,
>                                           void **payload)
>  {
>      int ret, request_ret;
> -    NBDReply local_reply;
> +    NBDReply local_reply = { 0, };

Yesterday [2] Peter said: "= {}" is our standard struct-zero-initializer
so we should prefer that.

With {}:
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

>      NBDStructuredReplyChunk *chunk;
>      Error *local_err = NULL;
>      if (s->quit) {
> 

[1] https://lists.gnu.org/archive/html/qemu-devel/2019-02/msg07007.html
[2] https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg03431.html