The signal handler modification check is showing a signal handler change when there is none.
jcmd PID VM.info and hs_err reports contain this info. e.g.
$ jdk-19/bin/jcmd 17446 VM.info
...
Signal Handlers:
SIGSEGV: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGBUS: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGFPE: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGPIPE: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGXFSZ: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGILL: javaSignalHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGUSR2: SR_handler in libjvm.so, mask=00000000000000000000000000000000, flags=SA_RESTART|SA_SIGINFO
SIGHUP: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGINT: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGTERM: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
SIGQUIT: UserHandler in libjvm.so, mask=11100100010111111101111111111110, flags=SA_RESTART|SA_SIGINFO
*** Handler was modified!
*** Expected: javaSignalHandler in libjvm.so, mask=11100100110111111111111111111110, flags=SA_RESTART|SA_SIGINFO
SIGTRAP: SIG_DFL, mask=00000000000000000000000000000000, flags=none
NOT in jdk-19-ea+6
IS in jdk-19-ea+7 and later
This is happending after:
8279124: VM does not handle SIGQUIT during initialization
In src/hotspot/os/posix/signals_posix.cpp
PosixSignals::print_signal_handler() prints the "Handler was modified!" text.
It checks if the saved expected action is non-null, not whether we have
do_check_signal_periodically[sig] == true
But although set_signal_handler has a parameter do_check, we always populate the SavedSignalHandlers vm_handlers even when this is false.