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

* Andi Kleen <andi@firstfloor.org> 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.

No, it does not assume it: if a particular usecase cares *so* little
about updates that it won't ever update their userland and kernel
then they have no problem: they'll have what they had before.

If they are willing to update the *kernel* then they will have to
consider what every kernel update brings with itself: legacy
facilities are de-emphasised all the time (while the ABI is still
fully guaranteed) so user-space should not assume that newer kernels
will offer the exact same performance tradeoffs as before.

Nor do i think have you cited any *real* example - you are just
talking hypotheticals with very little specifics. ABI does not mean
'executes the same instructions', guaranteeing that would be crazy.

Thanks,

Ingo


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