RFR: 8295159: DSO created with -ffast-math breaks Java floating-point arithmetic [v8]

[Magnus Ihse Bursie]

On Wed, 11 Oct 2023 13:31:22 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 with a new target base due to a merge or a rebase. The pull request now contains 28 commits:
> 
>  - Merge branch 'JDK-8295159' of https://github.com/theRealAph/jdk into JDK-8295159
>  - Fix LLVM
>  - Give x32 bug its own ID.
>  - cleanup
>  - Fix conditional compilation
>  - Remove x32 handling
>  - Stash x86-32 changes
>  - MacOS
>  - AArch64
>  - x86-32 changes
>  - ... and 18 more: https://git.openjdk.org/jdk/compare/cef9fff0...c56adbd9

make/autoconf/flags-cflags.m4 line 577:

> 575:   # CXXFLAGS C++ language level for all of JDK, including Hotspot.
> 576:   if test "x$TOOLCHAIN_TYPE" = xgcc || test "x$TOOLCHAIN_TYPE" = xclang || test "x$TOOLCHAIN_TYPE" = xxlc; then
> 577:     LANGSTD_CXXFLAGS="-std=gnu++14"

Uhhh, is this really okay? I thought the idea was that we should standardize on official C++, not use vendor-specific extensions. 

@kimbarrett Opinions on this?

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PR Review Comment: https://git.openjdk.org/jdk/pull/10661#discussion_r1338190849