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

[Geert Uytterhoeven]

Hi Yamada-san,

On Wed, Jan 24, 2024 at 9:13 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> On Wed, Jan 24, 2024 at 5:56 PM Yoann Congal <yoann.congal@xxxxxxxx> wrote:
> > Le 24/01/2024 à 09:09, Masahiro Yamada a écrit :
> > > On Wed, Jan 24, 2024 at 12:11 AM Yoann Congal <yoann.congal@xxxxxxxx> wrote:
> > >> Le 23/01/2024 à 13:54, Geert Uytterhoeven a écrit :
> > >>> On Sat, Nov 25, 2023 at 5:36 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> 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@xxxxxxxxxx>
> > >>>
> > >>> 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?
> >
> > My first test shows that switching CONFIG_BASE_SMALL to bool type does fix the LOG_CPU_MAX_BUF_SHIFT default value.
> >
> > >> I'll poke around to see if I can understand why a int="0" is true for kconfig.
> >
> > Here's what I understood:
> > To get the default value of LOG_CPU_MAX_BUF_SHIFT, kconfig calls sym_get_default_prop(LOG_CPU_MAX_BUF_SHIFT)
> > -> expr_calc_value("BASE_SMALL" as an expr)
> > -> sym_calc_value(BASE_SMALL as a symbol) and returns sym->curr.tri
> >
> > But, if I understood correctly, sym_calc_value() does not set sym->currtri in case of a int type config.
>
> Right.
>
> The following will restore the original behavior.
>
> --- a/scripts/kconfig/symbol.c
> +++ b/scripts/kconfig/symbol.c
> @@ -349,12 +349,15 @@ void sym_calc_value(struct symbol *sym)
>         switch (sym->type) {
>         case S_INT:
>                 newval.val = "0";
> +               newval.tri = no;
>                 break;
>         case S_HEX:
>                 newval.val = "0x0";
> +               newval.tri = no;
>                 break;
>         case S_STRING:
>                 newval.val = "";
> +               newval.tri = no;
>                 break;
>         case S_BOOLEAN:
>         case S_TRISTATE:

Thank you, that works for me.
Tested-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds