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evas_cpu: Avoid SIGILL in evas startup on x86

Authored by ManMower on Jun 18 2018, 1:12 PM.

Description

evas_cpu: Avoid SIGILL in evas startup on x86

Summary:
To determine if a system supports SIMD instructions, the cpuid facility
should be used. However, for 15+ years EFL has been trapping SIGILL,
then attempting to execute these intstructions.

Continuing after SIGILL is explicitly undefined behaviour and can never
safely be relied upon - it is possible the CPU will respond to the
unknown instruction in an upredictable way and the program will not
continue correctly. Even if it hasn't caused problems before, there's
no reason to believe a processor released in the future won't behave
differently.

Lately we've had a couple of bug tickets where SIGILL appears to cause
problems at a system level as well, but there seems little point in
chasing those problems down as we shouldn't even be doing this in the
first place.

ref T6711
ref T6989

We still rely on SIGILL in a few configurations where eina_cpu doesn't
know how to query features properly (powerpc, sparc, and non linux
ARM configurations). Hopefully someone with expertise on those
platforms can follow up and we can remove this entirely.

Note: MMX2 appears to not really be a thing, and is instead provided by
both 3DNow! and SSE. We already conflate it with SSE in other parts of
evas, so I've just used SSE here to test for its presence.
Depends on D6313

Reviewers: devilhorns, zmike

Reviewed By: zmike

Subscribers: cedric, committers, zmike

Tags: efl

Maniphest Tasks: T6989, T6711

Differential Revision: https://phab.enlightenment.org/D6314