linux-kernel - Re: [PATCH] media: do not use C++ style comments in uapi headers

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Date:   Tue, 4 Jun 2019 22:32:17 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Joe Perches <joe@...ches.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: do not use C++ style comments in uapi headers

On Tue, Jun 4, 2019 at 9:48 PM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
>
> On Tue, Jun 4, 2019 at 8:55 PM Arnd Bergmann <arnd@...db.de> wrote:
> >
> > On Tue, Jun 4, 2019 at 1:23 PM Joe Perches <joe@...ches.com> wrote:
> > >
> > > On Tue, 2019-06-04 at 20:13 +0900, Masahiro Yamada wrote:
> > > > On the other hand, uapi headers are written in more strict C, where
> > > > the C++ comment style is forbidden.
> > >
> > > Is this a real problem for any toolchain?
> >
> > There is likely some code that is built with -Wpedandic -Werror --std=c89
> > or similar. Since glibc allows this combination for its own headers, it seems
> > best to also allow it in kernel headers that may be included by libc headers
> > or by applications, at least where it does not hurt.
> >
> > Realistically though, we probably assume c99 or gnu89 in user space
> > headers anyway, since there is no 'long long' in earlier standards.
> >
> >        Arnd
>
> In fact, I detected this issue by the following patch:
> https://patchwork.kernel.org/patch/10974669/
>
> When I worked on it, I wondered which
> c-dialect flags should be used.
>
> This code:
>
> > # Unlike the kernel space, uapi headers are written in more strict C.
> > #  - Forbid C++ style comments
> > #  - Use '__inline', '__asm__' instead of 'inline', 'asm'
> > #
> > # -std=c90 (equivalent to -ansi) catches the violation of those.
> > # We cannot go as far as adding -Wpedantic since it emits too many warnings.
> > #
> > # REVISIT: re-consider the proper set of compiler flags for uapi compile-test.
> >
> > UAPI_CFLAGS := -std=c90 -Wpedantic -Wall -Werror=implicit-function-declaration


I got rid of -Wpedantic in the submitted patch.
Sorry if I confused you.


--
Best Regards
Masahiro Yamada