There are a few issues with the signal handler modification check in src/hotspot/os/posix/signals_posix.cpp:

The periodic warning triggers when crash_handler is the handler: should be ignored, as it is in PosixSignals::print_signal_handler().

check_signal_handler(int) prints ALL signal handlers when it finds one that is modified.  When multiple changes are detected, this is very noisy.

Code duplication/inconsistency.  Noted in PR for JDK-8283337, different code uses different guards for checking for changes handlers.