linux-kernel - Re: [Linux-fbdev-devel] fb: modedb uses wrong default

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Date:	Mon, 20 Nov 2006 12:05:21 -0800
From:	Andrew Morton <akpm@...l.org>
To:	James Simmons <jsimmons@...radead.org>
Cc:	linux-fbdev-devel@...ts.sourceforge.net,
	Tero Roponen <teanropo@....fi>, linux-kernel@...r.kernel.org
Subject: Re: [Linux-fbdev-devel] fb: modedb uses wrong default_mode

On Mon, 20 Nov 2006 16:48:05 +0000 (GMT)
James Simmons <jsimmons@...radead.org> wrote:

> > > 	    db = modedb;
> > > 	dbsize = ARRAY_SIZE(modedb);
> > > 
> > > 	if (!default_mode)
> > > 	    default_mode = &db[DEFAULT_MODEDB_INDEX];
> > > 	if (!default_bpp)
> > > 	    default_bpp = 8;
> > > 
> > > db will always be set.
> > 
> > I think we do need dbsize, and that the code which I have now:
> 
> I really don't trust dbsize. The driver writer can pass in the wrong 
> number.

That would be a bug.

> Whereas ARRAY_SIZE will always be correct. Lets take the position 
> that we use dbsize then we need to test if dbsize is greater than the 
> really size of the modedb. The dbsize parameter was for the days before we
> had ARRAY_SIZE.
> 
> > int fb_find_mode(struct fb_var_screeninfo *var,
> > 		 struct fb_info *info, const char *mode_option,
> > 		 const struct fb_videomode *db, unsigned int dbsize,
> > 		 const struct fb_videomode *default_mode,
> > 		 unsigned int default_bpp)
> > {
> >     int i;
> > 
> >     /* Set up defaults */
> >     if (!db) {
> > 	db = modedb;
> > 	dbsize = ARRAY_SIZE(modedb);
> >     }
> 
>       if (dbsize > ARRAY_SIZE(db))
> 	dbsize = ARRAY_SIZE(db);

We can't do ARRAY_SIZE on a random pointer like this: the compiler needs to
see the full definition of the array itself, and that is back in the
caller's compilation unit.


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