linux-kernel - Re: [PATCH] sparc: mdesc: Fix compile error seen with gcc 11.x

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Message-ID: <CAK8P3a1mrZHHfN0dK6nV3jpBmnYm+jG=M8j2u=1=ZPkLuf2DXQ@mail.gmail.com>
Date:   Tue, 14 Sep 2021 16:53:35 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     David Laight <David.Laight@...lab.com>,
        Sam Ravnborg <sam@...nborg.org>,
        "David S . Miller" <davem@...emloft.net>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sparc: mdesc: Fix compile error seen with gcc 11.x

On Tue, Sep 14, 2021 at 4:24 PM Guenter Roeck <linux@...ck-us.net> wrote:
> On 9/14/21 7:17 AM, David Laight wrote:
> >> Sorry, I didn't realize that a field of size 0 increases the structure size
> >> on sparc. I had checked the size of the old and the new structure with gcc
> >> on x86_64 and didn't see a field size increase.
> >
> > clang output doesn't change:
> >
> > https://godbolt.org/z/bTeeq19j1
> >
> > gcc ought to generate the same size.
> >
> > It ought to be 'char data[];' though.
> >
>
> I am never sure if [] or [0] is "correct". Anyway, is there agreement that this
> is an acceptable solution ? I'll be happy to resend if that is the case.

Yes, looks good to me, in the [] version. I think the [0] version can be
interpreted as a zero-length array that may not be accessed, while the
[] flexible array syntax clearly means that extra data follows, and it's
part of the C standard now, while [0] is a gcc extension.

        Arnd