linux-kernel - Re: [PATCH] kconfig: Warn if choice default is not in choice

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Message-ID: <CAFkk2KRAMu43Y87C+0CrNU3xs63bWuN=+kkVm0wsug95KwOi2A@mail.gmail.com>
Date:   Wed, 4 Oct 2017 02:10:59 +0200
From:   Ulf Magnusson <ulfalizer@...il.com>
To:     yann.morin.1998@...e.fr, linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Ulf Magnusson <ulfalizer@...il.com>
Subject: Re: [PATCH] kconfig: Warn if choice default is not in choice

On Wed, Oct 4, 2017 at 1:25 AM, Ulf Magnusson <ulfalizer@...il.com> wrote:
> This will catch mistakes like in the following real-world example, where
> a "CONFIG_" prefix snuck in, making an undefined symbol the default:
>
>         choice
>                 prompt "Compiler optimization level"
>                 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
>
>         config CC_OPTIMIZE_FOR_PERFORMANCE
>                 ...
>
>         config CC_OPTIMIZE_FOR_SIZE
>                 ...
>
>         endchoice
>
> This now prints the following warning:
>
>         init/Kconfig:1036:warning: choice default symbol 'CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE' is not contained in the choice
>
> Cases where the default symbol belongs to the wrong choice are also
> detected.
>
> (The mistake is harmless here: Since the default symbol is not visible,
> the choice falls back on using the first visible symbol as the default,
> which is CC_OPTIMIZE_FOR_PERFORMANCE, as intended.)
>
> Discovered while playing around with Kconfiglib
> (https://github.com/ulfalizer/Kconfiglib).
>
> Signed-off-by: Ulf Magnusson <ulfalizer@...il.com>
> ---
>  scripts/kconfig/menu.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
> index e935793..ce88de8 100644
> --- a/scripts/kconfig/menu.c
> +++ b/scripts/kconfig/menu.c
> @@ -252,6 +252,16 @@ static void sym_check_prop(struct symbol *sym)
>                                             "'%s': number is invalid",
>                                             sym->name);
>                         }
> +                       if (sym_is_choice(sym)) {
> +                               struct property *choice_prop =
> +                                       sym_get_choice_prop(sym2);
> +
> +                               if (!choice_prop ||
> +                                   prop_get_symbol(choice_prop) != sym)
> +                                       prop_warn(prop,
> +                                                 "choice default symbol '%s' is not contained in the choice",
> +                                                 sym2->name);
> +                       }
>                         break;
>                 case P_SELECT:
>                 case P_IMPLY:
> --
> 2.7.4
>

A patch to fix the compiler optimization level choice has been
submitted as well:
https://lkml.org/lkml/2017/10/3/991

Cheers,
Ulf