linux-kernel - Re: [PATCH 1/2] kconfig: remove unneeded symbol

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Date: Wed, 24 Jan 2024 17:09:52 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Yoann Congal <yoann.congal@...le.fr>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.org>, 
	Vegard Nossum <vegard.nossum@...cle.com>
Subject: Re: [PATCH 1/2] kconfig: remove unneeded symbol_empty variable

On Wed, Jan 24, 2024 at 12:11 AM Yoann Congal <yoann.congal@...le.fr> wrote:
>
> Le 23/01/2024 à 13:54, Geert Uytterhoeven a écrit :
> > Hi Yamada-san,
>
> Hello,
>
> > On Sat, Nov 25, 2023 at 5:36 PM Masahiro Yamada <masahiroy@...nel.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@...nel.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_SHIFT,
> > the aforementioned commit causes a change in the generated .config:
> >
> > -CONFIG_LOG_CPU_MAX_BUF_SHIFT=12
> > +CONFIG_LOG_CPU_MAX_BUF_SHIFT=0
> >
> > It looks like CONFIG_BASE_SMALL=0 is treated as a string instead of
> > the integer number zero?
> >
> > init/Kconfig=config LOG_CPU_MAX_BUF_SHIFT
> > init/Kconfig-   int "CPU kernel log buffer size contribution (13 => 8
> > KB, 17 => 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=0
>   CONFIG_BASE_FULL=y
>   CONFIG_BASE_SMALL=0
> 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=12 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=12
CONFIG_BASE_FULL=y
CONFIG_BASE_SMALL=0
















>
> 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 == 0
>   drivers/tty/vt/vc_screen.c:#define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)
>   include/linux/threads.h:#define PID_MAX_DEFAULT (CONFIG_BASE_SMALL ? 0x1000 : 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_SMALL ? 128 : 256)
>   include/linux/xarray.h:#define XA_CHUNK_SHIFT           (CONFIG_BASE_SMALL ? 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="0" is true for kconfig.
>
> Regards,
> --
> Yoann Congal
> Smile ECS - Tech Expert
>


-- 
Best Regards
Masahiro Yamada