RFR: 8294594: Fix cast-function-type warnings in signal handling code [v2]

[Kim Barrett]

On Tue, 11 Oct 2022 08:11:02 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> > > Fix looks good as far as it goes (can't believe I didn't see what was going on here!) - but `os::signal` is still broken as it uses `sa_handler` instead of `sa_sigaction`.
> > 
> > 
> > Yikes! I think this change should proceed as is, and `os::signal` should be looked at as a new issue. That looks messy :(
> 
> There is no rush, because we are waiting for another build system change to drop.
> 
> Why can't we do the same thing we did for `SR_handler` in `SR_initialize`?
> 
> ```
> @@ -864,7 +864,7 @@ void* os::signal(int signal_number, void* handler) {
>    remove_error_signals_from_set(&(sigAct.sa_mask));
>  
>    sigAct.sa_flags   = SA_RESTART|SA_SIGINFO;
> -  sigAct.sa_handler = CAST_TO_FN_PTR(sa_handler_t, handler);
> +  sigAct.sa_sigaction = CAST_TO_FN_PTR(sa_sigaction_t, handler);
>  
>    if (sigaction(signal_number, &sigAct, &oldSigAct)) {
>      // -1 means registration failed
> ```
> 
> It matches what we should do for `SIG_INFO` flag, and as Kim said, it is still likely yields the same code as `sa_handler` and `sa_sigaction` are probably the same on currently supported systems.

For POSIX we expect the handler argument for os::signal to be a sigaction handler (taking 3 arguments).  For Windows we expect os::signal to take a 1 argument handler, since Windows seemingly doesn't support the sigaction stuff.  How is that a portability layer?

So all of the calls are going to need their handler functions examined.  In at least one use (in os_windows), the UserHandler function takes 3 arguments though only uses one, and is called with only one.

Looking at where os::signal is called, it's not clear it needs to be in os, and given the inconsistent expectations it probably shouldn't be.  All calls are in posix-specific or windows-specific files.  I'd suggest removing os::signal entirely, and having windows code use ::signal and posix code use ::sigaction.  Maybe with some convenience wrappers around each, but those wrappers are windows-specific or posix-specific and never the twain shall meet.

That all seems to me like it would be better to separate from this change, keeping this one nice and simple.

-------------

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