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

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Date:	Mon, 20 Nov 2006 20:37:08 +0000 (GMT)
From:	James Simmons <jsimmons@...radead.org>
To:	Andrew Morton <akpm@...l.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


> > I really don't trust dbsize. The driver writer can pass in the wrong 
> > number.
> 
> That would be a bug.

Excuse my paranoia about what driver writers will do :-/

> > 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.

Good point about the pointer being valid. In that case we have to deal 
with dbsize. Still nervous about going out of bounds of the array.

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