Re: drivers/block/ub.c

["David S. Miller" <davem@redhat.com>]

On Mon, 28 Jun 2004 22:57:11 +0200
Oliver Neukum <oliver@neukum.org> wrote:

> Am Montag, 28. Juni 2004 22:25 schrieb David S. Miller:
> > That's true.  But if one were to propose such a feature to the gcc
> > guys, I know the first question they would ask.  "If no padding of
> > the structure is needed, why are you specifying this new
> > __nopadding__ attribute?"
> 
> It would replace some uses of __packed__, where the first element
> is aligned.

You have not considered what is supposed to happen when this
structure is embedded within another one.  What kind of alignment
rules apply in that case?  For example:

struct foo {
	u32	x;
	u8	y;
	u16	z;
} __attribute__((__packed__));

struct bar {
	u8		a;
	struct foo 	b;
};

That is why __packed__ can't assume the alignment of any structure
instance whatsoever.  Your __nopadding__ attribute proposal would
lay out struct bar differently in order to meet the alignment guarentees
you say it will be able to meet.