linux-kernel - Re: Kconfig: '+config' valid syntax?

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Date:	Thu, 02 Jul 2015 14:10:05 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Andreas Ruprecht <andreas.ruprecht@....de>,
	Valentin Rothberg <valentinrothberg@...il.com>
Cc:	rafael.j.wysocki@...el.com, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	hengelein Stefan <stefan.hengelein@....de>,
	linux@...inikbrodowski.net
Subject: Re: Kconfig: '+config' valid syntax?

[Spoiler: please start at the end of my reply.]

On do, 2015-07-02 at 13:57 +0200, Andreas Ruprecht wrote:
> On 07/02/2015 11:01, Paul Bolle wrote:
> > On Thu, 2015-07-02 at 10:08 +0200, Valentin Rothberg wrote:
> > 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.
> 
> This is _almost_ true (which I think is the problem). The rule for "."
> is empty, and not the same rule as for \n.

I see. That's nice to know.

>  So what happens here, is that
> any unknown characters are simply ignored until something in {n}+ 
> shows up.

How can unknown characters be part of {n}+?

> If I add something like the following instead:
> +	. {
> +		fprintf(stderr, "something else: %s\n", yytext);
> +		BEGIN(INITIAL);
> +	}
> 
> then Kconfig prints the message for the "+", but unfortunately also 
> lots
> of "-" (which come from the occasional "---help---" instead of "help".
> As it looks to me, they are only ignored one step later inside the
> <PARAM> case.

(Years ago I submitted a few trivial cleanups for typos regarding "--
-help---". I should have followed up on those cleanups with a patch to
remove the silly lex rule that just ignores "---".

Perhaps we should add an actual definition for "---help---". On the
other hand: last time I checked nothing actually cares about the "---"
markers so adding them achieves nothing. Cleaning all Kconfig files to
get rid of these markers is probably not worth it. Add a checkpatch rule
to warn about their uselessness?)

> So changing it like the above is not the solution, but at least we 
> know
> where the silent ignore is coming from...
> 
> Any idea how to properly fix this?

As I said in my follow up: see commit 2e0d737fc76f ("kconfig: don't
silently ignore unhandled characters").

Thanks,


Paul Bolle
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