RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v5]

[Andrew Haley]

On Wed, 12 Oct 2022 15:48:25 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Do we need to shuffle^W sort includes in this patch? I presume you'd want this patch to be cleanly backportable, which means it should probably be as point-y as it can get.

OK, I can back that part out.

> src/hotspot/os/linux/os_linux.cpp line 1747:
> 
>> 1745: void * os::Linux::dlopen_helper(const char *filename, char *ebuf,
>> 1746:                                 int ebuflen) {
>> 1747:   // JDK-8295159: Protect floating-point environment.
> 
> We need to be more verbose in these comments. Say something like:
> 
> 
> There are known cases where global library initialization sets the FPU flags
> that affect computation accuracy, for example, enabling Flush-To-Zero and
> Denormals-Are-Zero. Do not let those libraries break the Java arithmetic.
> Unfortunately, this might break the libraries that might depend on these FPU
> features for performance and/or numerical "accuracy", but we need to protect 
> the Java semantics first and foremost. See JDK-8295159.

Thanks, that is elegantly expressed.

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