> x86-64 long mode does not support many of the things
> you listed, save for variable length instructions.
Actually I think it supports all of them!
Well you got me there. I read some more of the manuals, and you are mostly right. Some of the things I assumed were defunct or changed in x86-64 long mode (like the top-half-of-register stuff), are still alive and kicking. I guess changing some of these behaviors would have caused drastic compiler changes, so it was decided not to do it. They took the easy route, which is sort of a shame, but I can't blame them too much. Stirring up the pot too much might have resulted in more resistance in adoption.
By the way, some of old instructions, including the two you listed, are no longer valid in long mode. That is of little consequence compared to some of the other stuff that is still in there.
So x86 sucks. I hate to even play a side to it, but I do because I'm investing in AMD. The thing is, it doesn't really matter that it sucks, because it has such a foothold, and even with all the legacy crud, processors based on it still manage to churn out excellent performance. This may not hold true forever, and I recognize that.
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