RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v9]

[Florian Weimer]

On Wed, 11 Oct 2023 17:29:11 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:
> 
>   Add TestDenormalDouble.java

test/hotspot/jtreg/compiler/floatingpoint/libfast-math.c line 37:

> 35: 
> 36: #if defined(__GNUC__)
> 37: static void __attribute__((constructor)) set_flush_to_zero(void) {

Maybe add a comment that the ELF constructor is there to mimic historic GCC `-ffast-math` behavior on compilers that have been fixed not to do this for `-shared`?

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PR Review Comment: https://git.openjdk.org/jdk/pull/10661#discussion_r1356543707