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From: DJ Delorie <dj@redhat.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: tunables vs osxsave vs checkpointing vs _dl_runtime_resolve
In-Reply-To: <87mtv0qr8v.fsf@oldenburg.str.redhat.com> (message from Florian
 Weimer on Thu, 18 Mar 2021 18:57:36 +0100)
Date: Thu, 18 Mar 2021 14:19:28 -0400
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Florian Weimer <fweimer@redhat.com> writes:
> The layout matters only if the process is captured at a very unlucky
> time.

Unlucky?  Ha!  I *plan* on that kind of bad luck!

Call sleep(10).  Checkpoint during that call.  Crash on return.

>> In this case, they just want to disable xsave completely, so it's as
>> portable as possible.
>
> But I don't think it actually is.  Disabling XSAVE won't play nicely
> with the AVX2 and later calling conventions.

That's the YMMV caveat - they have to ensure that they're not using
extended registers *at all*.  I don't recommend it.  It's bad practice.
But we still have a tunable that's ignored, for people who want it
anyway.