linux-kernel - Re: [PATCH] staging: greybus: Replace zero-length array with flexible-array

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Message-ID: <20200513154807.GA25962@localhost>
Date:   Wed, 13 May 2020 17:48:07 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johan Hovold <johan@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Alex Elder <elder@...nel.org>, greybus-dev@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: greybus: Replace zero-length array with
 flexible-array

On Wed, May 13, 2020 at 05:39:18PM +0200, Greg Kroah-Hartman wrote:
> On Wed, May 13, 2020 at 05:03:43PM +0200, Johan Hovold wrote:
> > On Thu, May 07, 2020 at 01:53:18PM -0500, Gustavo A. R. Silva wrote:
> > > The current codebase makes use of the zero-length array language
> > > extension to the C90 standard, but the preferred mechanism to declare
> > > variable-length types such as these ones is a flexible array member[1][2],
> > > introduced in C99:
> > > 
> > > struct foo {
> > >         int stuff;
> > >         struct boo array[];
> > > };

> > >  drivers/greybus/arpc.h                    |    2 -
> > >  include/linux/greybus/greybus_protocols.h |   44 +++++++++++++++---------------
> > 
> > I noticed Greg just applied this one to his -testing branch, but do we
> > really want this in greybus_protocols.h, which is meant to be shared
> > with the firmware side? Perhaps not an issue, just figured I'd point
> > this out.
> 
> Why not, it should be the same thing, right?  No logic has changed that
> I see.

Yes, the structure's the same, but the firmware toolchain may not
expect flexible arrays. I believe we're holding back on these changes
for uapi headers as well for that reason?

Again, perhaps not an issue. We can just mandate fw toolchains that
support C99 if you want to use an unmodified header, I guess.

Johan