GNATS-1110: in_cksum_hdr error in PC386 BSP

[Ralf Corsepius]

On Wed, 2006-07-05 at 13:47 -0500, Eric Norum wrote:
> I'm beginning to think that we really ought to just switch over to the
> C version which was posted with the original problem report.
I'm inclined to agree. In particular, from my experience, in many cases,
GCC is doing a pretty good job at optimizing byte ops etc., and thereby
rendering things much easier maintenance-wise. 

> > Till Straumann wrote:
> > 
> > 
> > > I just found another problem with
> > > in_cksum_hdr (freebsd mailing list).
> > > 
> > > 
> > > Currently, (i386, ppc) the algorithm is split into several
> > > 'asm' constructs and we assume that the carry bit
> > > is preserved across these. This is not a valid assumption,
> > > however.
This explanation makes sense - I had a gut feeling the explanation might
be along these lines, but didn't dare to pronounce it ;)
 
> > > 
> > Does their code base have a fixed version?
> > 
> > 
> > > We definitively should try harder to eliminate 'asm'
> > > 
> > > 
> > Unfortunately, it is a necessary evel.
Really? Did anybody analyze the asm resulting from using the C version
of these routines?
Unless they perform significantly worse than asm, or unless the asm is
eye-strikingly simple (which it had not been), I would not think using
asm is still worth it.

Ralf