On Wed, Mar 06, 2019 at 04:44:04PM +0000, Jason Gunthorpe wrote:
> 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?
I would be glad to see other solution, but I don't know such.
>
> Jason
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