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

[Andrew Haley]

On Wed, 12 Oct 2022 20:35:09 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> Isn't it an illustration of a more general problem we have with native code where it can mess with FP environment at any time?

Yes.

> We already have similar problems with MXCSR register and provide verification logic (part of `-Xcheck:jni`) to catch modifications and support conditional restoration of MXCSR register on x86_64. x86_32 validates x87 control word when `-Xcheck:jni` is enabled.
> 
> Should we do something similar here instead?

The problem is that this bug is very insidious: the user probably doesn't know that there's anything wrong, and almost certainly has no idea that it's anything to do with JNI.

Saving and restoring the floating-point environment across dlopen() is a compromise between adding extra code at JNI callouts, which can be expensive, and shifting the burden to the user.

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