Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls

[Ingo Molnar <mingo@elte.hu>]

* pageexec@freemail.hu <pageexec@freemail.hu> wrote:

> On 8 Jun 2011 at 12:06, Andi Kleen wrote:
> 
> > > eventually may even go away as time progresses and linux 
> > > systems begin to fully rely on the vdso instead.
> > 
> > That assumes that everyone uses glibc and also updates their 
> > userland. As pointed out many times that's a deeply flawed 
> > assumption.
> 
> i think the assumption is not that everyone uses glibc but that 
> everyone else (as in, every other libc) can simply take the 
> necessary changes from glibc, provided they need such changes at 
> all (i.e., they're using the vsyscall entry points over the vdso 
> ones).
> 
> i frankly didn't check any of the alternatives myself 
> (uclibc/klibc/bionic/etc) but i can't imagine that it'd be that 
> much harder to patch them than glibc.

Correct. Also, as i pointed it out in the previous mail, ABI does not 
mean 'will execute the same instructions', that would be silly. We 
*do* fix serious wide-scale performance regressions (obviously), but 
if it's about some weird crazy legacy path that we had good security 
reasons to change, and which is trivial to performance-improve in the 
library then we are well within our boundaries to keep the change.

> as i said, this was a compromise solution but then i think you 
> already made it clear that you didn't even think there was a 
> problem here to solve, so i guess we should work that out first, if 
> you want to ;).

Heh, indeed ;-)

Thanks,

	Ingo