Date: Tue, 25 Oct 2016 08:40:29 +0300
From: Leon Romanovsky <leonro@mellanox.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Doug Ledford <dledford@redhat.com>, Sean Hefty <sean.hefty@intel.com>,
        Hal Rosenstock <hal.rosenstock@gmail.com>,
        Matan Barak <matanb@mellanox.com>, Sagi Grimberg <sagig@mellanox.com>,
        Bart Van Assche <bart.vanassche@sandisk.com>,
        Noa Osherovich <noaos@mellanox.com>,
        Saeed Mahameed <saeedm@mellanox.com>, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] IB/mlx5: avoid bogus -Wmaybe-uninitialized warning
Message-ID: <20161025054029.GM25013@leon.nu>
References: <20161024204830.620592-1-arnd@arndb.de>
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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 =E2=80=98mlx5_ib_reg_user_mr=E2=80=
=99:
> infiniband/hw/mlx5/mr.c:1172:5: error: =E2=80=98order=E2=80=99 may be use=
d uninitialized in this function [-Werror=3Dmaybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1161:6: note: =E2=80=98order=E2=80=99 was declare=
d here
> infiniband/hw/mlx5/mr.c:1173:6: error: =E2=80=98ncont=E2=80=99 may be use=
d uninitialized in this function [-Werror=3Dmaybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1160:6: note: =E2=80=98ncont=E2=80=99 was declare=
d here
> infiniband/hw/mlx5/mr.c:1173:6: error: =E2=80=98page_shift=E2=80=99 may b=
e used uninitialized in this function [-Werror=3Dmaybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1158:6: note: =E2=80=98page_shift=E2=80=99 was de=
clared here
> infiniband/hw/mlx5/mr.c:1143:13: error: =E2=80=98npages=E2=80=99 may be u=
sed uninitialized in this function [-Werror=3Dmaybe-uninitialized]
> infiniband/hw/mlx5/mr.c:1159:6: note: =E2=80=98npages=E2=80=99 was declar=
ed 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@mellanox.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/infiniband/hw/mlx5/mr.c | 39 +++++++++++++++++++++--------------=
----
>  1 file changed, 21 insertions(+), 18 deletions(-)
>
> v2: fix whitespace typo

Thanks

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