linux-kernel - Re: [PATCH] rbd: work around -Wuninitialized warning

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Date:   Wed, 8 Jan 2020 16:31:36 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sage Weil <sage@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Oleksandr Natalenko <oleksandr@...hat.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Jason Dillaman <dillaman@...hat.com>,
        David Howells <dhowells@...hat.com>,
        Ceph Development <ceph-devel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rbd: work around -Wuninitialized warning

On Tue, Jan 7, 2020 at 10:02 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> gcc -O3 warns about a dummy variable that is passed
> down into rbd_img_fill_nodata without being initialized:
>
> drivers/block/rbd.c: In function 'rbd_img_fill_nodata':
> drivers/block/rbd.c:2573:13: error: 'dummy' is used uninitialized in this function [-Werror=uninitialized]
>   fctx->iter = *fctx->pos;
>
> Since this is a dummy, I assume the warning is harmless, but
> it's better to initialize it anyway and avoid the warning.
>
> Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/block/rbd.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 29be02838b67..070edc5983df 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -2664,7 +2664,7 @@ static int rbd_img_fill_nodata(struct rbd_img_request *img_req,
>                                u64 off, u64 len)
>  {
>         struct ceph_file_extent ex = { off, len };
> -       union rbd_img_fill_iter dummy;
> +       union rbd_img_fill_iter dummy = {};
>         struct rbd_img_fill_ctx fctx = {
>                 .pos_type = OBJ_REQUEST_NODATA,
>                 .pos = &dummy,

Applied, but slightly confused.  Wasn't selecting -O3/s/etc supposed to
automatically disable -Wmaybe-uninitialized via Kconfig?

Thanks,

                Ilya