Re: [patch-2.4.0-test2]Re: Linux-2.4.0-test2

[Horst von Brand]

Urban Widmark <[e-mail]> said:
> On Sat, 24 Jun 2000, Tigran Aivazian wrote:
> > K&R says (page 213, A8.3):
> > 
> >    Adjacent field members of structures are packed into
> >    implementation-dependent storage units in an implementation-dependent
> >    direction. ... The members of a structure have addresses increasing in
> >    the order of their declaration.  
> > 
> > I think Alan Cox is right - there is no guarantee that field members of a
> > structure can be found one after another starting from the first field.

AFAIU, the "implementation dependent direction" here is big vs
little enedian, at most. See that that _addresses_ are guaranteed to be
increasing. Modulo padding (which in the example below isn't applicable
anywhere I know), they are the same anywhere.

> So all drivers (I'm sure there are a few) that use something like
> 
> struct foo {
> 	u32	a;
> 	u32	b;
> 	u32	c;
> 	u32	d;
> }
> 
> to communicate with some hardware (4 32-bit values with addresses in
> sequence) should be fixed not to make assumptions about the layout of a
> struct?

This would break one of the important uses of C (hardware fiddling) big
way.
-- 
Horst von Brand                             [e-mail]
Casilla 9G, Vin~a del Mar, Chile                               [phone]