Re: [PATCH 1/2] kconfig: remove unneeded symbol_empty variable

Yoann Congal
2024-01-23T15:11:07Z

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@kernel.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_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.

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