Re: [PATCH 4/11] use ether_addr_equal_64bits

[Ben Greear]

On 12/31/2013 08:09 AM, Julia Lawall wrote:
> 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.

You mean 16 bits?

> But maybe something with sizeof(foo) and offset_of would do?
>
> Could the macro be put near the declaration of the structure somehow?

I think that would work, but do not know all of the details of such
macros, so it's possible there is some catch.

If nothing else, then some run-time code that calculates the offset off
and asserts if it is broken in module initialization or similar might
be good enough.

Thanks,
Ben

--
Ben Greear <greearb@xxxxxxxxxxxxxxx>
Candela Technologies Inc  http://www.candelatech.com

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