Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

[Florian Weimer]

* Dave Hansen via Libc-alpha:

> Our system calls are *REALLY* fast.  We can even do a vsyscall for this
> if we want to get the overhead down near zero.  Userspace can also cache
> the "I did the prctl()" state in thread-local storage if it wants to
> avoid the syscall.

Why can't userspace look at XCR0 to make the decision?

And we added an interface for querying x86 CPU features to glibc 2.33
which is completely incompatible with this because it assumes that CPU
features do not change during the lifetime of a process. 8-(

Thanks,
Florian