RFR: 8292695: SIGQUIT and jcmd attaching mechanism does not work with signal chaining library

[David Holmes]

On Sat, 20 Aug 2022 22:43:03 GMT, Man Cao <manc at openjdk.org> wrote:

> Hi all,
> 
> Could anyone review this bug fix? See https://bugs.openjdk.org/browse/JDK-8292695 for details.
> 
> I changed the temporary handler for SIGQUIT to use a dummy function, and use `os::signal()` to set it up, just as `os::initialize_jdk_signal_support()` does.
> It is possible that just moving the `set_signal_handler(BREAK_SIGNAL, false);` in `install_signal_handlers()` outside of the window bounded by `JVM_{begin|end}_signal_setting()` could also fix this bug. However, `set_signal_handler()` and `JVM_HANDLE_XXX_SIGNAL()` are currently used for signals that support chaining and periodically check, which do not apply to SIGQUIT. I think it is cleaner to use different functions for SIGQUIT.
> 
> I also added a test to check that sending SIGQUIT should produce a thread dump on stdout, with and without using libjsig.so.
> 
> -Man

src/hotspot/os/posix/signals_posix.cpp line 1345:

> 1343:     // JVM_begin_signal_setting and JVM_end_signal_setting above, because the
> 1344:     // window is intended for signals that support chaining. Otherwise libjsig
> 1345:     // would prevent us from overwriting BREAK_SIGNAL's handler to UserHandler.

Okay but doesn't that also mean that libjsig will now allow application code to install its own BREAK_SIGNAL handler, when it should be prevented from doing so???

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PR: https://git.openjdk.org/jdk/pull/9955