RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v15]

[Thomas Stuefe]

On Thu, 26 Oct 2023 14:17:02 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:
> 
>   Duh

One more thought, it would be good to add the FTZ_mode_enabled check to `os::run_periodic_checks()`. 

We already do signal handler checks there, and it is the right place to check for "global things third party native code may mess up". It runs when one uses `-XX:CheckJNICalls`. If a native library messes with fenv, one will get a delayed assertion, with a hs-err file that lists all the shared objects.

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PR Comment: https://git.openjdk.org/jdk/pull/10661#issuecomment-1781408815