Re: Hammer on snapshot cd's

[Joerg Sonnenberger <joerg@xxxxxxxxxxxxxxxxx>]

On Wed, Jul 16, 2008 at 05:12:02PM +0800, Sepherosa Ziehau wrote:
> > There seems to be a traditional, irrational fear of -O2 in the FreeBSD
> > community, which I can't explain.  I've heard something about -O2 and inline
> > assembly, but that's probably old as well.

Like the horrible mess they do for the ip checksumming...
Frankly, I believe most of that is due to bad inline assembly specs...

> I think it something about accessing (or dereferencing) unaligned
> fields in a union.

-O2 turns on -fstrict-aliasing by default, which means that two types
can only overlap, if they one is char or share definition. That's a bit
simplified. It is something you really want to explicitly turn off for a
kernel...

Joerg