RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v7]

[Andrew Haley]

On Mon, 31 Oct 2022 18:25:57 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> > Anyway, I plan to
> > a. Restore the FPU CR after calls to dlopen(3).
> > b. Detect FPU CR corruption at safepoints, and print a warning. At least
> > the user might find out that something is wrong.
> 
> Doing (a) seems good. I can't say for sure whether (b) is a good idea. I guess you just have some call to verify the FPU, e.g. in `ParallelCleanupTask`? I assume you don't mean to change the code for polling safepoints.

My intention is only to do the FPU CR  check when there is an expensive operation such as moving to s safepoint. That we we won't see a significant slowdown. But we are pretty much guaranteed that the user won't get incorrect results without some sort of diagnostic.

> CSR seems like a good idea, since it could be a change in observable behavior. (nice to leave a paper trail I think)

Yep.

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PR: https://git.openjdk.org/jdk/pull/10661