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

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Message-ID: <YkKhc2BbkmdVwKex@kroah.com>
Date:   Tue, 29 Mar 2022 08:04:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        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 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>