linux-kernel - Re: [PATCH v2] IB/mlx5: avoid bogus -Wmaybe-uninitialized warning

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Date:   Tue, 25 Oct 2016 08:40:29 +0300
From:   Leon Romanovsky <leonro@...lanox.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Doug Ledford <dledford@...hat.com>,
        Sean Hefty <sean.hefty@...el.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>,
        Matan Barak <matanb@...lanox.com>,
        Sagi Grimberg <sagig@...lanox.com>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Noa Osherovich <noaos@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] IB/mlx5: avoid bogus -Wmaybe-uninitialized warning

On Mon, Oct 24, 2016 at 10:48:21PM +0200, Arnd Bergmann wrote:
> We get a false-positive warning in linux-next for the mlx5 driver:
>
> infiniband/hw/mlx5/mr.c: In function ‘mlx5_ib_reg_user_mr’:
> infiniband/hw/mlx5/mr.c:1172:5: error: ‘order’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1161:6: note: ‘order’ was declared here
> infiniband/hw/mlx5/mr.c:1173:6: error: ‘ncont’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1160:6: note: ‘ncont’ was declared here
> infiniband/hw/mlx5/mr.c:1173:6: error: ‘page_shift’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1158:6: note: ‘page_shift’ was declared here
> infiniband/hw/mlx5/mr.c:1143:13: error: ‘npages’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1159:6: note: ‘npages’ was declared here
>
> I had a trivial workaround for gcc-5 or higher, but that didn't work
> on gcc-4.9 unfortunately.
>
> The only way I found to avoid the warnings for gcc-4.9, short of
> initializing each of the arguments first was to change the calling
> conventions to separate the error code from the umem pointer. This
> avoids casting the error codes from one pointer to another incompatible
> pointer, and lets gcc figure out when that the data is actually valid
> whenever we return successfully.
>
> Acked-by: Leon Romanovsky <leonro@...lanox.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/infiniband/hw/mlx5/mr.c | 39 +++++++++++++++++++++------------------
>  1 file changed, 21 insertions(+), 18 deletions(-)
>
> v2: fix whitespace typo

Thanks

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