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

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Date:   Tue, 29 Mar 2022 16:16:02 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.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 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.



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/



-- 
Best Regards
Masahiro Yamada