Received-SPF: pass (google.com: domain of linux-kernel+bounces-38744-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
References: <20231125163559.824210-1-masahiroy@kernel.org> <CAMuHMdWm6u1wX7efZQf=2XUAHascps76YQac6rdnQGhc8nop_Q@mail.gmail.com>
 <d21298d9-fed6-4e08-9780-dbcb388b9ccc@smile.fr> <CAK7LNASaG4DpHTb3YHMd8d8DJ5H3z0aiUcSqX+=7CZb99kRU8A@mail.gmail.com>
 <b65a68eb-6b96-41ff-bbb9-38cb2dee940e@smile.fr> <CAK7LNARVbjVkP=v7uQDB=Z+Ntcy9MiFa6WowTX9mA47YjS3zTg@mail.gmail.com>
In-Reply-To: <CAK7LNARVbjVkP=v7uQDB=Z+Ntcy9MiFa6WowTX9mA47YjS3zTg@mail.gmail.com>
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Thu, 25 Jan 2024 15:48:09 +0100
Message-ID: <CAMuHMdUkQb6GSC2XmZHCf5hCmQ9XEW+T2r+jyjy92La4gZvGkg@mail.gmail.com>
Subject: Re: [PATCH 1/2] kconfig: remove unneeded symbol_empty variable
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Yoann Congal <yoann.congal@smile.fr>, linux-kbuild@vger.kernel.org, 
	linux-kernel@vger.kernel.org, 
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>, 
	Vegard Nossum <vegard.nossum@oracle.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Yamada-san,

On Wed, Jan 24, 2024 at 9:13=E2=80=AFPM Masahiro Yamada <masahiroy@kernel.o=
rg> wrote:
> On Wed, Jan 24, 2024 at 5:56=E2=80=AFPM Yoann Congal <yoann.congal@smile.=
fr> wrote:
> > Le 24/01/2024 =C3=A0 09:09, Masahiro Yamada a =C3=A9crit :
> > > On Wed, Jan 24, 2024 at 12:11=E2=80=AFAM Yoann Congal <yoann.congal@s=
mile.fr> wrote:
> > >> Le 23/01/2024 =C3=A0 13:54, Geert Uytterhoeven a =C3=A9crit :
> > >>> On Sat, Nov 25, 2023 at 5:36=E2=80=AFPM 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=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 i=
ssue.
> > >>> Also reverting commit 6262afa10ef7cc8f ("kconfig: default to zero i=
f
> > >>> int/hex symbol lacks default property") does fix it.
> > >>
> > >> (Since I'd really like 6262afa10ef7cc8f ("kconfig: default to zero i=
f 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.

> > >> 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=
 ? 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_BA=
SE_SMALL ? 128 : 256)
> > >>   include/linux/xarray.h:#define XA_CHUNK_SHIFT           (CONFIG_BA=
SE_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=3D"0" is true =
for kconfig.
> >
> > Here's what I understood:
> > To get the default value of LOG_CPU_MAX_BUF_SHIFT, kconfig calls sym_ge=
t_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->curr=
tri 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 =3D "0";
> +               newval.tri =3D no;
>                 break;
>         case S_HEX:
>                 newval.val =3D "0x0";
> +               newval.tri =3D no;
>                 break;
>         case S_STRING:
>                 newval.val =3D "";
> +               newval.tri =3D no;
>                 break;
>         case S_BOOLEAN:
>         case S_TRISTATE:

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

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds