On Wed, Mar 06, 2019 at 02:37:17PM +0200, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@xxxxxxxxxxxx>
>
> Attempt to use check_shl_overflow() with inputs of unsigned type
> produces the following compilation warnings.
>
> drivers/infiniband/hw/mlx5/qp.c: In function _set_user_rq_size_:
> ./include/linux/overflow.h:230:6: warning: comparison of unsigned
> expression >= 0 is always true [-Wtype-limits]
> _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
> ^~
> drivers/infiniband/hw/mlx5/qp.c:5820:6: note: in expansion of macro _check_shl_overflow_
> if (check_shl_overflow(rwq->wqe_count, rwq->wqe_shift,
> &rwq->buf_size))
> ^~~~~~~~~~~~~~~~~~
> ./include/linux/overflow.h:232:26: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
> (_to_shift != _s || *_d < 0 || _a < 0 || \
> ^
> drivers/infiniband/hw/mlx5/qp.c:5820:6: note: in expansion of macro _check_shl_overflow_
> if (check_shl_overflow(rwq->wqe_count, rwq->wqe_shift, &rwq->buf_size))
> ^~~~~~~~~~~~~~~~~~
> ./include/linux/overflow.h:232:36: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
> (_to_shift != _s || *_d < 0 || _a < 0 || \
> ^
> drivers/infiniband/hw/mlx5/qp.c:5820:6: note: in expansion of macro _check_shl_overflow_
> if (check_shl_overflow(rwq->wqe_count, rwq->wqe_shift,&rwq->buf_size))
> ^~~~~~~~~~~~~~~~~~
>
> Fixes: 0c66847793d1 ("overflow.h: Add arithmetic shift helper")
> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
> Changelog v0->v1:
> * fixed wrong checks
> include/linux/overflow.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 40b48e2133cb..a47fb6046c0a 100644
> +++ b/include/linux/overflow.h
> @@ -227,10 +227,10 @@
> typeof(d) _d = d; \
> u64 _a_full = _a; \
> unsigned int _to_shift = \
> - _s >= 0 && _s < 8 * sizeof(*d) ? _s : 0; \
> + (_s == 0 || _s > 0) && _s < 8 * sizeof(*d) ? _s : 0; \
I think this is just trading a tautological compare gcc happens to
know about today (_s >= 0) with one it currently doesn't (_s == 0 ||
_s > 0)
Maybe cc the various people that helped review this macro and see if
we can find another solution?
Jason
