Re: Updated version of RD/WR FS/GS BASE patchkit

[Andi Kleen]

> So a patchset to enable these asinine new instructions needs to take
> this into account, and the ABI issue needs to be addressed, even if

What's the ABI issue?

AFAIK we're perfectly consistent.

> the answer is that the proposed code is fine.
> 
> (Also, the existing code is fscked up.  Guess what xor %eax, %eax; mov
> %ax, %gs does to the base on AMD?  The existing code is *wrong*, and I
> don't want to see it get wronger.)

I have no idea, but changing it is definitely not in scope for my patches.

> 
> And no, I don't really care about programs detecting context switches.
> I do, however, care about allowing non-determinism in things that
> ought to behave deterministically.  Writing a nonzero value to %gs and
> then doing WRGSBASE is something that user code will be able to do
> whether we like it or not, some shitty threading library is likely to
> do this just to spite us, the the kernel needs to do *something* when
> this happens.

They will quickly notice it if there is a problem, so I don't think
we need to worry about that.

-Andi

-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.