Xtonlsab bug

[Ondrej Zajicek]

On Thu, Apr 29, 2010 at 11:57:32PM +0200, Joakim Tjernlund wrote:
> 
> Ondrej Zajicek <santiago at crfreenet.org> wrote on 2010/04/29 23:15:22:
> >
> > On Thu, Apr 29, 2010 at 11:03:32PM +0200, Joakim Tjernlund wrote:
> > >
> > > Ondrej, this looks buggy:
> > >
> > > +static inline void htonlsab(void *h, void *n, u16 len) { memcpy(n, h, len); };
> > > +static inline void ntohlsab(void *n, void *h, u16 len) { memcpy(h, n, len); };
> > >
> > > memcpy is not defined to handle overlapping memory. Best to add:
> > > if (n != h)
> > >   memcpy(...)
> >
> > Yes, but all usages of htonlsab()/ntohlsab() are non-overlapping.
> > (overlapping/on place usage was replaced with htonlsab1()/ntohlsab1()).
> 
> I see, but it would be safer to have that check in case you
> used them in the wrong way?

I think this is no issue. Even if someone used them in a wrong way
(which is improbable, as these functions are used just in a few
places), memcpy() would probably do nothing when src==dst (although
it is unspecified).

> > > Might as well do that for these too:
> > > +static inline void htonlsah(struct ospf_lsa_header *h, struct
> > ospf_lsa_header *n) { *n = *h; };
> > > +static inline void ntohlsah(struct ospf_lsa_header *n, struct
> > ospf_lsa_header *h) { *h = *n; };
> >
> > *n = *h should be OK even if n == h, AFAIK.
> 
> Hopyfully, but isn't gcc allowed to use memcpy to do that
> assignment?

Definitely isn't allowed to do something that breaks the specified
behavior of C operators.

> If you add that if (h!=n) test, doesn't the need for Xlasb1() go away as well?

I think it is cleaner to have Xlsab1() for that purpose.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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