Re: [patch 2.6.22-rc2-git] spidev compiler warning gone

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

On Tuesday 29 May 2007, Andrew Morton wrote:
> On Fri, 25 May 2007 10:35:07 -0700
> David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org> wrote:
> 
> > Get rid of annoying GCC warning on 32-bit platforms.  The trick is to
> > add an extra cast using "ptrdiff_t" to convert the u64 to the correct
> > size integer, and only then casting it into a "void *" pointer.
> > 
> >	...
> > -			if (__copy_to_user((u8 __user *)u_tmp->rx_buf, buf,
> > +			if (__copy_to_user((u8 __user *)
> > +					(ptrdiff_t) u_tmp->rx_buf, buf,
> > 	...
> 
> This seems overly tricky.  The way we normally squish that warning is
> via a (long) cast.

Well, "ptrdiff_t" seems equivalent to "long" in common cases.

Presumably C99 guarantees pointer-to-long conversions work in
both directions?  It seemed there must necessarily be such a
guarantee for "ptrdiff_t", even if it weren't true for "long".
I didn't have a copy of a C spec to consult.  ;)

- Dave

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/