linux-kernel - Re: [PATCH] IB/qib: Fix null pointer subtraction compiler warning

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Date:   Wed, 8 Sep 2021 08:44:20 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        linux-rdma@...r.kernel.org
Cc:     Leon Romanovsky <leonro@...dia.com>,
        kernel test robot <lkp@...el.com>,
        Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IB/qib: Fix null pointer subtraction compiler warning

On Fri, Sep 03, 2021 at 10:07:28AM -0300, Jason Gunthorpe wrote:
> >> drivers/infiniband/hw/qib/qib_sysfs.c:411:1: warning: performing pointer subtraction with a null pointer has undefined behavior
> +[-Wnull-pointer-subtraction]
>    QIB_DIAGC_ATTR(rc_resends);
>    ^~~~~~~~~~~~~~~~~~~~~~~~~~
>    drivers/infiniband/hw/qib/qib_sysfs.c:408:51: note: expanded from macro 'QIB_DIAGC_ATTR'
>                    .counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0,    \
> 
> Use offsetof and accomplish the type check using static_assert.
> 
> Fixes: 4a7aaf88c89f ("RDMA/qib: Use attributes for the port sysfs")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Acked-by: Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>
> ---
>  drivers/infiniband/hw/qib/qib_sysfs.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Applied to for-rc

Jason