linux-kernel - Re: [PATCH] RDMA/hfi1: use a struct group to avoid warning

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Message-Id: <e477f8c0-5478-43b5-9d59-297efc32d20e@app.fastmail.com>
Date: Tue, 08 Apr 2025 14:40:38 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Jason Gunthorpe" <jgg@...pe.ca>, "Arnd Bergmann" <arnd@...nel.org>
Cc: "Dennis Dalessandro" <dennis.dalessandro@...nelisnetworks.com>,
 "Leon Romanovsky" <leon@...nel.org>, "Steven Rostedt" <rostedt@...dmis.org>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 "Jani Nikula" <jani.nikula@...el.com>,
 Christian König <christian.koenig@....com>,
 linux <linux@...blig.org>, "Maher Sanalla" <msanalla@...dia.com>,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RDMA/hfi1: use a struct group to avoid warning

On Mon, Apr 7, 2025, at 20:27, Jason Gunthorpe wrote:
> On Thu, Apr 03, 2025 at 04:47:53PM +0200, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>> 
>> On gcc-11 and earlier, the driver sometimes produces a warning
>> for memset:
>> 
>> In file included from include/linux/string.h:392,
>>                  from drivers/infiniband/hw/hfi1/mad.c:6:
>> In function 'fortify_memset_chk',
>>     inlined from '__subn_get_opa_hfi1_cong_log' at drivers/infiniband/hw/hfi1/mad.c:3873:2,
>>     inlined from 'subn_get_opa_sma' at drivers/infiniband/hw/hfi1/mad.c:4114:9:
>> include/linux/fortify-string.h:480:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror]
>>     __write_overflow_field(p_size_field, size);
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 
>> This seems to be a false positive, and I found no nice way to rewrite
>> the code to avoid the warning, but adding a a struct group works.
>
> Er.. so do we really want to fix it or just ignore this on gcc-11? Or
> is there really a compile bug here and it is mis-generating the code?
>
> The unneeded struct group seems ugly to me?

Having a clean build would be nice though. Do you think a patch
that just turns off the warning locally would be better?

      Arnd