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

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Date:   Tue, 5 May 2020 17:00:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
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 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.

       Arnd