linux-kernel - Re: [PATCH v2 04/21] kconfig: reference environments directly and remove 'option env=' syntax

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Date:   Fri, 30 Mar 2018 14:30:49 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Ulf Magnusson <ulfalizer@...il.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Nicolas Pitre <nico@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v2 04/21] kconfig: reference environments directly and
 remove 'option env=' syntax

2018-03-29 11:19 GMT+09:00 Ulf Magnusson <ulfalizer@...il.com>:.

>>  %%
>> +static void expand_string(const char *in)
>> +{
>> +       char *p, *q;
>> +
>> +       p = expand_string_value(in);
>> +
>> +       q = p + strlen(p);
>> +       while (q > p)
>> +               unput(*--q);
>> +
>> +       free(p);
>> +}
>> +
>
> I like the simplicity of this approach, but I suspect it might be too simple.
>
> For example, the following breaks with a syntax error if $ENV has any
> double quotes in its value:
>
>     config FOO
>         string "foo"
>         default "$ENV"
>
> The following will only work as expected if $ENV expands to a valid
> Kconfig symbol name. If it doesn't, random stuff will happen (most
> likely a syntax error).
>
>     config FOO
>         string "foo"
>         default $ENV
>
> The reason it works if $ENV expands to a valid symbol name is that
> undefined symbols get their name as their (string) value. If the
> symbol happens to be defined, it will be referenced, which seems
> confusing too.
>
> In general, that reinterpretation of expanded values feels a bit icky
> to me, and as something that might add complexity to Kconfig for
> little value. If $ENV outside of quotes absolutely must be supported,
> I think it should be a shorthand for "$ENV" (which means "constant
> value" in Kconfig speak).
>

You are right.  This implementation is too lazy, and bad.
I will change the implementation.

Thanks.




-- 
Best Regards
Masahiro Yamada