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    SubjectRe: Kconfig: '+config' valid syntax?
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    [Dropped Yann. You already know Yann disappeared.]

    On Thu, 2015-07-02 at 10:08 +0200, Valentin Rothberg wrote:
    > commit ed013214afa7 ("ACPI / init: Make it possible to override _REV")
    > is in today's linux-next tree (i.e., next-20150702) adding the
    > following hunk to drivers/acpi/Kconfig:
    >
    > --- a/drivers/acpi/Kconfig
    > +++ b/drivers/acpi/Kconfig
    > @@ -428,6 +428,26 @@ config XPOWER_PMIC_OPREGION
    > help
    > This config adds ACPI operation region support for XPower
    > AXP288 PMIC.
    >
    > ++config ACPI_REV_OVERRIDE_POSSIBLE

    (Odd. Botched conflict resolution?)

    > + bool "Allow supported ACPI revision to be overriden"
    > + depends on X86
    > + default y
    > [...]
    >
    > By having a close look at the first added line, we can see that
    > '+config ACPI_...' is added. To my great surprise, it's valid Kconfig
    > syntax.

    I played a bit with this. It seems you can basically add a '+' anywhere
    you like and kconfig will just ignore it.

    > How is that possible? IMHO it's an invalid token, such that
    > Kconfig should complain about it. Or do I miss something?

    Welcome to the wonders of lex and yacc!

    I try to spend as little time as possible looking at the lex rules, so
    I'm just guessing here. Anyhow, you might start by looking at this
    snippet in zconf.l:
    . {
    unput(yytext[0]);
    BEGIN(COMMAND);
    }


    <COMMAND>{
    {n}+ {
    [...]
    }
    .
    \n {
    BEGIN(INITIAL);
    current_file->lineno++;
    return T_EOL;
    }
    }

    Which perhaps translates to:
    - ignore unknown stuff for now and go in COMMAND state;
    - do something if we encounter some text ({n} = [A-Za-z0-9_]);
    - go in INITIAL state if we encounter newlines or unknown stuff.

    At the end of which we're back where we started before encountering
    the'+'. But there are more references to '.' in the lex rules so it's
    probably more complicated.

    Hope this helps,


    Paul Bolle


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