[crac] RFR: 8373027: [CRaC] [CRIU] x86: FPU xsave area present, but host cpu doesn't support it

[Radim Vansa]

On Wed, 3 Dec 2025 15:08:08 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

> In some cases (such as AWS `t3.nano` -> `m1.small`) CRIU refuses to restore:
> 
> x86: FPU xsave area present, but host cpu doesn't support it
> 
> 
> I think (based on information of @rvansa `xsave` is not needed for the safepoint of JDK checkpoint/restore.

I thought that we +- control native threads through `glibc.cpu.hwcaps`, don't we? Except for hand-written assembly and similar. We should not give up on native threads in general.

I think that in order to prove that the test above is efficient, you'd have to verify where are the safepoint injection points (as the executing thread will be stopped on safepoint before proceeding to checkpoint), and that a variable is stored in FPU register (not on stack) across the safepoint/checkpoint. 
(I don't know what are the current rules for safepoint injection, I hope that it will inject some safepoints even to those counted loops when it sees that these have 16M iterations).

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PR Comment: https://git.openjdk.org/crac/pull/279#issuecomment-3657059725