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