linux-kernel - Re: [PATCH] pinctrl: renesas: no need to initialise global statics

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Message-ID: <CAMuHMdWPSofFJcSQHwvGy=E-T74QK2v3L60+feLJ-kEfB3GY5A@mail.gmail.com>
Date:   Tue, 7 Sep 2021 13:01:58 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jason Wang <wangborong@...rlc.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: renesas: no need to initialise global statics

On Mon, Sep 6, 2021 at 5:18 PM Arnd Bergmann <arnd@...db.de> wrote:
> On Mon, Sep 6, 2021 at 4:36 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > --- a/drivers/pinctrl/renesas/core.c
> > > +++ b/drivers/pinctrl/renesas/core.c
> > > @@ -741,12 +741,12 @@ static int sh_pfc_suspend_init(struct sh_pfc *pfc) { return 0; }
> > >  #define SH_PFC_MAX_REGS                300
> > >  #define SH_PFC_MAX_ENUMS       3000
> > >
> > > -static unsigned int sh_pfc_errors __initdata = 0;
> > > -static unsigned int sh_pfc_warnings __initdata = 0;
> > > -static u32 *sh_pfc_regs __initdata = NULL;
> > > -static u32 sh_pfc_num_regs __initdata = 0;
> > > -static u16 *sh_pfc_enums __initdata = NULL;
> > > -static u32 sh_pfc_num_enums __initdata = 0;
> > > +static unsigned int sh_pfc_errors __initdata;
> > > +static unsigned int sh_pfc_warnings __initdata;
> > > +static u32 *sh_pfc_regs __initdata;
> > > +static u32 sh_pfc_num_regs __initdata;
> > > +static u16 *sh_pfc_enums __initdata;
> > > +static u32 sh_pfc_num_enums __initdata;
> >
> > These are special, as they use __initdata.
> > While dropping the initializers seems to work fine with e.g. gcc 9,
> > I'm quite sure that would fail with older compiler versions, where
> > the variable would be put in bss instead of initdata.
> >
> > See the example in include/linux/init.h, which explicitly
> > initializes a variable with zero:
> >
> >     static int init_variable __initdata = 0;
> >
> > Arnd: do you know in which version of gcc this was fixed?
> > It seems at least 6.5.0 and later are fine (I don't have all required
> > shared libs to run e.g. 5.5.0).
>
> I think you mixed up what happens: As far as I know, older compilers
> would put variables without the =0 into .bss, but those with the explicit
> =0 would end up in .data. Newer compilers treat them exactly the
> same, and these variables all get put into .bss by default. This seems
> to already be the case with gcc-4.1, which is the oldest one I could
> easily try.
>
> I'm rather sure that regardless of the compiler version, adding an
> explicit section attribute like the __initdata would force the section
> even on the pre-4.1 compilers.

I must be misremembering...

Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
i.e. will queue in renesas-pinctrl-for-v5.16.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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