Re: [PATCH rc] IB/qib: Fix clang confusion of NULL pointer comparison

[Nick Desaulniers <ndesaulniers@google.com>]

On Tue, Sep 14, 2021 at 12:01 PM Jason Gunthorpe <jgg@nvidia.com> wrote:
>
> clang becomes confused due to the comparision to NULL in a contexpr context:

s/comparision/comparison/

s/contexpr/Integer Constant Expression/

I don't think constexpr is the equivalent to an ICE. We know what you
mean though. :^)

>
>  >> drivers/infiniband/hw/qib/qib_sysfs.c:413:1: error: static_assert expression is not an integral constant expression
>     QIB_DIAGC_ATTR(rc_resends);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~
>     drivers/infiniband/hw/qib/qib_sysfs.c:406:16: note: expanded from macro 'QIB_DIAGC_ATTR'
>             static_assert(&((struct qib_ibport *)0)->rvp.n_##N != (u64 *)NULL);    \
>
> Nick found __same_type that solves this problem nicely, so use it instead.

Sorry, Nathan found that.  Should be:

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Thanks for the patch.

>
> Reported-by: kernel test robot <lkp@intel.com>
> Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/infiniband/hw/qib/qib_sysfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Hopefully third time is the charm here..

:^)

>
> diff --git a/drivers/infiniband/hw/qib/qib_sysfs.c b/drivers/infiniband/hw/qib/qib_sysfs.c
> index 452e2355d24eeb..0a3b28142c05b6 100644
> --- a/drivers/infiniband/hw/qib/qib_sysfs.c
> +++ b/drivers/infiniband/hw/qib/qib_sysfs.c

Consider explicitly including <linux/compiler_types.h> in this
translation unit.  I know it may compile today, and it might just be
our internal style guide talking here...

> @@ -403,7 +403,7 @@ static ssize_t diagc_attr_store(struct ib_device *ibdev, u32 port_num,
>  }
>
>  #define QIB_DIAGC_ATTR(N)                                                      \
> -       static_assert(&((struct qib_ibport *)0)->rvp.n_##N != (u64 *)NULL);    \
> +       static_assert(__same_type(((struct qib_ibport *)0)->rvp.n_##N, u64));  \
>         static struct qib_diagc_attr qib_diagc_attr_##N = {                    \
>                 .attr = __ATTR(N, 0664, diagc_attr_show, diagc_attr_store),    \
>                 .counter =                                                     \
>
> base-commit: 6880fa6c56601bb8ed59df6c30fd390cc5f6dd8f
> --
> 2.33.0
>


-- 
Thanks,
~Nick Desaulniers