Re: Makefile: CC_IMPLICIT_FALLTHROUGH passed quoted as argument to gcc

From: Masahiro Yamada <masahiroy@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Salvatore Bonaccorso <carnil@debian.org>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Makefile: CC_IMPLICIT_FALLTHROUGH passed quoted as argument to gcc
Date: Sun, 5 Dec 2021 02:54:05 +0900	[thread overview]
Message-ID: <CAK7LNAR-VXwHFEJqCcrFDZj+_4+Xd6oynbj_0eS8N504_ydmyw@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=whTTWUyL5j5_-UeRT6k9VcJM_VOfjiKuU2NBJkxhbnXpw@mail.gmail.com>

On Sun, Dec 5, 2021 at 1:53 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Sat, Dec 4, 2021 at 5:13 AM Salvatore Bonaccorso <carnil@debian.org> wrote:
> >
> > Andreas suggested to replace the
> >
> > KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
> >
> > with
> >
> > KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(patsubst "%",%,$(CONFIG_CC_IMPLICIT_FALLTHROUGH))
>
> Ugh. I think the external build environment is a bit broken, but
> whatever. The above is ugly but I guess it works.
>
> Another alternative would be to make the Kconfig strings simply not
> have '"' as part of them.
>
> When you do
>
>     a = "hello"
>     print $a
>
> in any normal language, you generally wouldn't expect it to print the
> quotes, it should just print the bare word.
>
> But that's what the Kconfig string language basically does in this
> case. And I guess several users expect and take advantage of that ;(
>
> Masahiro? Comments?

Yes, you get to the point.

In fact, this is in my TODO list for a while
(and this is the reason I was doing prerequisite Kconfig refactoring
in the previous development cycle).
I will try to find some spare time to complete this work.

Kconfig generates two similar files,

 -   .config
 -   include/config/auto.conf

Changing the format of the .config is presumably problematic
since it is the saved user configuration as well.

It is possible (and more reasonable) to change include/config/auto.conf
so strings are not quoted.

In Makefiles, quotations are just normal characters; they have no
special functionality.

So, in Makefile context, it is more handy to do

     CONFIG_X=foo bar

instead of

    CONFIG_X="foo bar"

One problem is include/config/auto.conf is included not only by Makefiles
but also by shell scripts.

In shell context, the right hand side must be quoted
in case the value contains spaces.

   CONFIG_X="foo bar"

My plan is to fix
  scripts/link-vmlinux.sh
  scripts/gen_autoksyms.sh
etc. to not directly include the auto.conf.
Later, change Kconfig to generate the auto.conf without "".

In the meantime,

KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(patsubst
"%",%,$(CONFIG_CC_IMPLICIT_FALLTHROUGH))

 or if you prefer slightly shorter form,

KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH:"%"=%)

will be a workaround.

>
>              Linus

-- 
Best Regards
Masahiro Yamada