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From: Amir Goldstein <amir73il@gmail.com>
Date: Wed, 6 Mar 2024 09:36:14 +0200
Message-ID: <CAOQ4uxg185+i+n_mnXsEaxXYJ1SseDH6RtGreTJDhjkOt6mmSA@mail.gmail.com>
Subject: Re: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end warning
To: Kees Cook <keescook@chromium.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>, Jan Kara <jack@suse.cz>, 
	Alexander Viro <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, 
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-hardening@vger.kernel.org
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On Wed, Mar 6, 2024 at 1:52=E2=80=AFAM Kees Cook <keescook@chromium.org> wr=
ote:
>
> On Tue, Mar 05, 2024 at 04:18:46PM -0600, Gustavo A. R. Silva wrote:
> > -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> > ready to enable it globally.
> >
> > There is currently a local structure `f` that is using a flexible
> > `struct file_handle` as header for an on-stack place-holder for the
> > flexible-array member `unsigned char f_handle[];`.
> >
> > struct {
> >       struct file_handle handle;
> >       u8 pad[MAX_HANDLE_SZ];
> > } f;
>
> This code pattern is "put a flex array struct on the stack", but we have
> a macro for this now:
>
> DEFINE_FLEX(struct file_handle, handle, f_handle, MAX_HANDLE_SZ);
>
> And you can even include the initializer:
>
> _DEFINE_FLEX(struct file_handle, handle, f_handle, MAX_HANDLE_SZ,
>              =3D { .handle_bytes =3D MAX_HANDLE_SZ });
>

Indeed that looks much nicer.

Thanks,
Amir.