Re: [PATCH][next] fsnotify: Avoid -Wflex-array-member-not-at-end warning

["Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>]

On 3/5/24 17:52, Kees Cook wrote:
> 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,
> 	     = { .handle_bytes = MAX_HANDLE_SZ });
>
> I think this would be a simpler conversion.
>
> Also, this could use a __counted_by tag...
>
> I need to improve the DEFINE_FLEX macro a bit, though, to take advantage
> of __counted_by.

Yep, I like it.

I'll go and hunt down all those on-stack -Wflex-array-member-not-at-end
issues with this helper. :)

Thanks
--
Gustavo