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

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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 ‘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@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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[PATCH v2] IB/mlx5: avoid bogus -Wmaybe-uninitialized warning Arnd Bergmann <arnd@arndb.de> - 2016-10-24 22:50 +0200
  Re: [PATCH v2] IB/mlx5: avoid bogus -Wmaybe-uninitialized warning Leon Romanovsky <leonro@mellanox.com> - 2016-10-25 07:50 +0200

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