linux-kernel - Re: [PATCH 2/2] kbuild: forbid exported headers from including <stdint.h>, <stdbool.h>

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Message-ID: <YkLhDMlImRBQuPWx@kroah.com>
Date:   Tue, 29 Mar 2022 12:35:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Elliot Berman <quic_eberman@...cinc.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 2/2] kbuild: forbid exported headers from including
 <stdint.h>, <stdbool.h>

On Tue, Mar 29, 2022 at 04:16:02PM +0900, Masahiro Yamada wrote:
> On Tue, Mar 29, 2022 at 3:04 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Tue, Mar 29, 2022 at 02:21:30AM +0900, Masahiro Yamada wrote:
> > > Some UAPI headers included <stdlib.h>, like this:
> > >
> > >   #ifndef __KERNEL__
> > >   #include <stdlib.h>
> > >   #endif
> > >
> > > As it turned out, they just included it for no good reason.
> > >
> > > After some fixes, now I can compile-test UAPI headers
> > > (CONFIG_UAPI_HEADER_TEST=y) without <stdlib.h> included.
> > >
> > > To avoid somebody getting it back again, this commit adds the dummy
> > > header, usr/dummy-include/stdlib.h
> > >
> > > I added $(srctree)/usr/dummy-include to the header search paths.
> > > Because it is searched before the system directories, if someone
> > > tries to include <stdlib.h>, they will see the error message.
> > >
> > > While I am here, I also replaced $(objtree)/usr/include with $(obj), but
> > > it is just a small refactoring.
> > >
> > > If we achieve the situation where none of system headers is included
> > > from exported kernel headers (i.e. kernel headers become self-contained),
> > > we might be able to add -nostdinc, but that is much far from where we
> > > stand now. (see many no-header-test lines in usr/include/Makefile)
> > >
> > > As a realistic solution, you can forbid header inclusion individually by
> > > putting a dummy header into usr/dummy-include/.
> > >
> > > Currently, no header include <stdbool.h>. I put it as well before somebody
> > > attempts to use it.
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> >
> > Nice work!
> >
> > Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> 
> I made a mistake in the patch subject.
> 
> The correct title should be:
> 
>     kbuild: forbid exported headers from including <stdlib.h>, <stdbool.h>
> 
> I will fix it in v2.

Ah, missed that, yes.

> We cannot ban <stdint.h> for now because there are still some users.
> 
> A fix-up patch exists, but the fuse maintainer was opposed to it.
> https://lore.kernel.org/lkml/20220318171405.2728855-1-cmllamas@google.com/

It's not ok for one lone file to break the rules that all other uapi
header files follow.  I think that needs to be fixed, there is NOTHING
special about that one subsystem to justify this.

Uniformity is good, and should be followed, and I strongly think that
change needs to be accepted.

thanks,

greg k-h