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

[David Holmes]

On Wed, 12 Oct 2022 17:00:15 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> A bug in GCC causes shared libraries linked with -ffast-math to disable denormal arithmetic. This breaks Java's floating-point semantics.
>> 
>> The bug is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55522
>> 
>> One solution is to save and restore the floating-point control word around System.loadLibrary(). This isn't perfect, because some shared library might load another shared library at runtime, but it's a lot better than what we do now. 
>> 
>> However, this fix is not complete. `dlopen()` is called from many places in the JDK. I guess the best thing to do is find and wrap them all. I'd like to hear people's opinions.
>
> Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8295159: DSO created with -ffast-math breaks Java floating-point arithmetic

None of this seems adequate. If you guard the dlopen this is a race as the thread doing the dlopen could get switched out leading to corruption in other threads. But we can't just simply save/restore across JNI calls either as we may save the bad env if the dlopen just occurred! The pre-existing "fixes" in this area seem similarly inadequate (and my recollection of issues was that this was an opt-in band-aid while people migrated away from using problematic native libraries, or else got them fixed).

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