linux-kernel - Re: [PATCH v2 2/2] lib.c: skip --param parameters

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Date:	Mon, 30 Jun 2014 11:32:45 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Christopher Li <sparse@...isli.org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux-Sparse <linux-sparse@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] lib.c: skip --param parameters

On Sat, 2014-06-28 at 09:59 -0700, Christopher Li wrote:
> Oops, I just click send before I type up the reply. Here we go again.
> 
> On Tue, Jun 17, 2014 at 2:11 AM, Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> > Very dumb patch to just skip --param allow-store-data-races=0 introduced in
> > newer GCC versions.
> >
> > +static char **handle_param(char *arg, char **next)
> > +{
> > +       const char *value = NULL;
> > +
> > +       /* For now just skip any '--param=*' or '--param *' */
> > +       value = split_value_from_arg(arg, value);
> > +       if (!value)
> > +               ++next;
> > +
> > +       return ++next;
> > +}
> 
> I think this is problematic.There are three possible input
> from args:
> 1) "--parm", you need to ++next skip to next arg, which is the value for parm.
> 2) "--parm=x",  you don't need to skip to next arg.
> 3) "--parm-with-crap", invalid argument. You don't need to skip next arg.
> 
> I think the patch is wrong on case 2) and case 3).
> In case 2), the patch skip two arguments and make next point
> points to out of bound memory.

Hmm... I'd just added test printf to the handle_param() and see if I
print *next, it is either --param or --param=*. So, using return (next +
2) helps, otherwise we end up with the same situation as before patch.

What did I miss?

> 
> The split_value_from_arg function is not a good abstraction for this job.
> Its return value can only indicate 2 possible out come.
> Also, returning the default value force the test against the input
> default value. That make the logic a bit complicate.
> 
> >  struct switches {
> >         const char *name;
> >         char **(*fn)(char *, char **);
> > @@ -686,13 +698,14 @@ struct switches {
> >  static char **handle_long_options(char *arg, char **next)
> >  {
> >         static struct switches cmd[] = {
> > +               { "param", handle_param },
> >                 { "version", handle_version },
> >                 { NULL, NULL }
> >         };
> >         struct switches *s = cmd;
> >
> >         while (s->name) {
> > -               if (!strcmp(s->name, arg))
> > +               if (!strncmp(arg, s->name, strlen(s->name)))
> 
> This will allow "--version-with-crap" as valid arguments.

Which was explicitly mentioned in the commit message.

> 
> I think we can have one extra member in "struct switch"
> to indicate this option is a prefix rather than a whole word.
> For "parm", it need to set that prefix member to non zero.

No objections about this approach.

> Please let me know if there is a V3 coming.

Apparently you did this on weekend.


-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy

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