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From: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
To: Jason Gunthorpe <jgg@nvidia.com>, linux-rdma@vger.kernel.org
Cc: Leon Romanovsky <leonro@nvidia.com>,
	kernel test robot <lkp@intel.com>,
	Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>,
	llvm@lists.linux.dev, kbuild-all@lists.01.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] IB/qib: Fix null pointer subtraction compiler warning
Date: Fri, 3 Sep 2021 13:24:41 -0400	[thread overview]
Message-ID: <fae8ef94-0684-bce5-ce3a-c25cfb5820df@cornelisnetworks.com> (raw)
In-Reply-To: <0-v1-43ae3c759177+65-qib_type_jgg@nvidia.com>

On 9/3/21 9:07 AM, 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@intel.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  drivers/infiniband/hw/qib/qib_sysfs.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/hw/qib/qib_sysfs.c b/drivers/infiniband/hw/qib/qib_sysfs.c
> index d57e49de6650be..452e2355d24eeb 100644
> --- a/drivers/infiniband/hw/qib/qib_sysfs.c
> +++ b/drivers/infiniband/hw/qib/qib_sysfs.c
> @@ -403,9 +403,11 @@ 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 struct qib_diagc_attr qib_diagc_attr_##N = {                    \
>  		.attr = __ATTR(N, 0664, diagc_attr_show, diagc_attr_store),    \
> -		.counter = &((struct qib_ibport *)0)->rvp.n_##N - (u64 *)0,    \
> +		.counter =                                                     \
> +			offsetof(struct qib_ibport, rvp.n_##N) / sizeof(u64)   \
>  	}
>  
>  QIB_DIAGC_ATTR(rc_resends);
> 
> base-commit: 6a217437f9f5482a3f6f2dc5fcd27cf0f62409ac
> 

Looks fine.

Acked-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>

  reply	other threads:[~2021-09-03 17:24 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-03 13:07 Jason Gunthorpe
2021-09-03 17:24 ` Dennis Dalessandro [this message]
2021-09-08 11:44 ` Jason Gunthorpe

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