[lkml]   [2015]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 7/8] x86: Add documentation for rd/wr fs/gs base
> If user code programs fs != 0 and fsbase != whatever is implied by fs
> and the GDT/LDT, what happens?

We load the value from the LDT/GDT.

> There's already a minor buglet in that
> area without wrfsbase, but fixing it would be a big performance hit
> because we don't have rdfsbase and rdgsbase to read the state
> efficiently. (Specifically, if we have gs == 0, gsbase == 0, but
> *saved* gsbase != 0, then we corrupt gsbase on context switch.)
> But, with the new instructions, we can do it simply, efficiently, and
> correctly in all cases. Let's do so.

We would need an instruction to write the index without changing the base.
That's not what the new instructions do.


-- -- Speaking for myself only

 \ /
  Last update: 2015-04-10 23:21    [W:0.076 / U:0.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site