RFR: 8294594: Fix cast-function-type warnings in signal handling code

[Kim Barrett]

On Sun, 9 Oct 2022 01:43:26 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> After [JDK-8294314](https://bugs.openjdk.org/browse/JDK-8294314), we would have signals_posix.cpp excluded with cast-function-type warning:
>
> test/hotspot/gtest/runtime/test_signals.cpp line 49:
> 
>> 47:   static void check_handlers() {
>> 48:     struct sigaction act, old_SIGFPE_act, old_SIGILL_act;
>> 49:     act.sa_handler = CAST_FROM_FN_PTR(sa_handler_t, sig_handler);
> 
> This is similarly wrong code that should be fixed instead of doing weird casting dances.  The problem here is that sig_handler has the wrong signature.  It should be just `void sig_handler(int)`.  Fix that and not casts needed.

This one is even worse than the other.  Here we're installing a handler function taking 3 arguments in such a way that it will only be called with one.  Weee!

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PR: https://git.openjdk.org/jdk/pull/10494