Re: [PATCH 4/11] use ether_addr_equal_64bits

Julia Lawall
2013-12-31T16:09:36Z

On Tue, 31 Dec 2013, Ben Greear wrote:

> On 12/30/2013 10:32 PM, Julia Lawall wrote:
> > > > > > I'm just thinking of a programmer, e.g. changing a struct like this:
> > > > > >
> > > > > > struct foo {
> > > > > > u8 addr[ETH_ALEN];
> > > > > > - u16 dummy;
> > > > > > };
> > >
> > > I don't know of a way to catch that.
> > > Anyone else?
> >
> > Well, one could have a semantic patch that checks for that. But the
> > problem is that it is very slow, and it only covers the cases that I can
> > transform automatically, which currently means no pointers, only explicit
> > arrays.
> >
> > On the other hand, I am finding the structure definition, so I can easily
> > update the structure definition with an appropriate comment.
> >
> > struct foo {
> > u8 addr[ETH_ALEN]; /* must be followed by two bytes in the structure */
> > u16 dummy;
> > };
> >
> > Unfortunately it is kind of verbose. Could there be an attribute? That
> > could even easily be checked.
>
> Can you not just add a build-time macro to check that sizeof(foo) >= 8
> for each of these struct foos? Or, is it required that the dummy field
> be there and be not used by anything else?

It doesn't matter what the field is used for. The problem is that is it
necessary to ensure a property of the position of addr within the
structure. It has to have at least 16 bytes after it.

But maybe something with sizeof(foo) and offset_of would do?

Could the macro be put near the declaration of the structure somehow?

julia