linux-kernel - Re: [PATCH] fsnotify: avoid gcc-10 zero-length-bounds warning

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Date:   Tue, 5 May 2020 10:11:39 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fsnotify: avoid gcc-10 zero-length-bounds warning



On 5/5/20 10:00, Arnd Bergmann wrote:
> On Tue, May 5, 2020 at 4:35 PM Gustavo A. R. Silva
> <gustavo@...eddedor.com> wrote:
>> On 5/5/20 09:30, Arnd Bergmann wrote:
>>> gcc-10 warns about accesses into the f_handle[] zero-length array.
>>>
>>> fs/notify/fdinfo.c: In function 'show_mark_fhandle':
>>> fs/notify/fdinfo.c:66:47: error: array subscript 'i' is outside the bounds of an interior zero-length array 'unsigned char[0]' [-Werror=zero-length-bounds]
>>>    66 |   seq_printf(m, "%02x", (int)f.handle.f_handle[i]);
>>>       |                              ~~~~~~~~~~~~~~~~~^~~
>>> In file included from fs/notify/fdinfo.c:3:
>>> include/linux/fs.h:988:16: note: while referencing 'f_handle'
>>>   988 |  unsigned char f_handle[0];
>>>       |                ^~~~~~~~
>>>
>>> This is solved by using a flexible array instead.
>>>
>>> Cc: Gustavo A. R. Silva <gustavo@...eddedor.com>
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>> ---
>>> Gustavo has done the same thing as part of a treewide change, but keeping
>>> this separate lets us backport it to stable kernels more easily later.
>>
>> Arnd,
>>
>> I wonder why would we need to backport these changes to -stable... merely
>> because of the use of a new version of GCC?
> 
> Yes, we usually backport trivial warning fixes to stable kernels to allow
> building those with any modern compiler version.
> 

OK. So, if you anticipate that this is going to happen, I can split up my
treewide patch into separate per-subsystem patches.  I can replace the
treewide patch in my tree today, so the changes are reflected in tomorrow's
linux-next.

--
Gustavo