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 <d21298d9-fed6-4e08-9780-dbcb388b9ccc@smile.fr>
In-Reply-To: <d21298d9-fed6-4e08-9780-dbcb388b9ccc@smile.fr>
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Wed, 24 Jan 2024 17:09:52 +0900
Message-ID: <CAK7LNASaG4DpHTb3YHMd8d8DJ5H3z0aiUcSqX+=7CZb99kRU8A@mail.gmail.com>
Subject: Re: [PATCH 1/2] kconfig: remove unneeded symbol_empty variable
To: Yoann Congal <yoann.congal@smile.fr>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>, linux-kbuild@vger.kernel.org, 
	linux-kernel@vger.kernel.org, 
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>, 
	Vegard Nossum <vegard.nossum@oracle.com>
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On Wed, Jan 24, 2024 at 12:11=E2=80=AFAM Yoann Congal <yoann.congal@smile.f=
r> wrote:
>
> Le 23/01/2024 =C3=A0 13:54, Geert Uytterhoeven a =C3=A9crit :
> > Hi Yamada-san,
>
> Hello,
>
> > On Sat, Nov 25, 2023 at 5:36=E2=80=AFPM Masahiro Yamada <masahiroy@kern=
el.org> wrote:
> >> This is used only for initializing other variables.
> >>
> >> Use the empty string "".
> >>
> >> Please note newval.tri is unused for S_INT/HEX/STRING.
> >>
> >> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> >
> > Thanks for your patch, which is now commit 4e244c10eab345a7
> > ("kconfig: remove unneeded symbol_empty variable") in v6.8-rc1.
> >
> > When running "make <foo>_defconfig" with <foo>_defconfig an SMP
> > defconfig without explicit configuration of CONFIG_LOG_CPU_MAX_BUF_SHIF=
T,
> > the aforementioned commit causes a change in the generated .config:
> >
> > -CONFIG_LOG_CPU_MAX_BUF_SHIFT=3D12
> > +CONFIG_LOG_CPU_MAX_BUF_SHIFT=3D0
> >
> > It looks like CONFIG_BASE_SMALL=3D0 is treated as a string instead of
> > the integer number zero?
> >
> > init/Kconfig=3Dconfig LOG_CPU_MAX_BUF_SHIFT
> > init/Kconfig-   int "CPU kernel log buffer size contribution (13 =3D> 8
> > KB, 17 =3D> 128KB)"
> > init/Kconfig-   depends on SMP
> > init/Kconfig-   range 0 21
> > init/Kconfig:   default 12 if !BASE_SMALL
> > init/Kconfig:   default 0 if BASE_SMALL
> >
> > Note that reverting 4e244c10eab345a7 is not sufficient to fix the issue=
.
> > Also reverting commit 6262afa10ef7cc8f ("kconfig: default to zero if
> > int/hex symbol lacks default property") does fix it.
>
> (Since I'd really like 6262afa10ef7cc8f ("kconfig: default to zero if int=
/hex symbol lacks default property") to stay, allow me to try to help)
>
> The problem is quite easy to reproduce:
>   $ make x86_64_defconfig
>   $ grep 'LOG_CPU_MAX_BUF_SHIFT\|BASE_SMALL\|BASE_FULL' .config
>   CONFIG_LOG_CPU_MAX_BUF_SHIFT=3D0
>   CONFIG_BASE_FULL=3Dy
>   CONFIG_BASE_SMALL=3D0
> Here, CONFIG_LOG_CPU_MAX_BUF_SHIFT should be 12 not 0.


I could not produce it in this way.
I ran the same commands as yours.

CONFIG_LOG_CPU_MAX_BUF_SHIFT=3D12 for me.


masahiro@zoe:~/ref/linux(master)$ git describe
v6.8-rc1-29-g615d30064886
masahiro@zoe:~/ref/linux(master)$ git diff
masahiro@zoe:~/ref/linux(master)$ make  x86_64_defconfig
#
# No change to .config
#
masahiro@zoe:~/ref/linux(master)$ grep
'LOG_CPU_MAX_BUF_SHIFT\|BASE_SMALL\|BASE_FULL' .config
CONFIG_LOG_CPU_MAX_BUF_SHIFT=3D12
CONFIG_BASE_FULL=3Dy
CONFIG_BASE_SMALL=3D0


>
> For what it is worth, CONFIG_BASE_SMALL is defined as an int but is only =
used as a bool :
>    $ git grep BASE_SMALL
>   arch/x86/include/asm/mpspec.h:#if CONFIG_BASE_SMALL =3D=3D 0
>   drivers/tty/vt/vc_screen.c:#define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 25=
6 : PAGE_SIZE)
>   include/linux/threads.h:#define PID_MAX_DEFAULT (CONFIG_BASE_SMALL ? 0x=
1000 : 0x8000)
>   include/linux/threads.h:#define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE=
_SIZE * 8 : \
>   include/linux/udp.h:#define UDP_HTABLE_SIZE_MIN         (CONFIG_BASE_SM=
ALL ? 128 : 256)
>   include/linux/xarray.h:#define XA_CHUNK_SHIFT           (CONFIG_BASE_SM=
ALL ? 4 : 6)
>   init/Kconfig:   default 12 if !BASE_SMALL
>   init/Kconfig:   default 0 if BASE_SMALL
>   init/Kconfig:config BASE_SMALL
>   kernel/futex/core.c:#if CONFIG_BASE_SMALL
>   kernel/user.c:#define UIDHASH_BITS      (CONFIG_BASE_SMALL ? 3 : 7)
>
> Maybe we should change CONFIG_BASE_SMALL to the bool type?
>
> I'll poke around to see if I can understand why a int=3D"0" is true for k=
config.
>
> Regards,
> --
> Yoann Congal
> Smile ECS - Tech Expert
>


--=20
Best Regards
Masahiro Yamada