(S) RFR: 8139300: Internal Error (vm/utilities/debug.cpp:399), # Error: ShouldNotReachHere()

[David Holmes]

Ping! Could I get a runtime reviewer as well please.

Thanks,
David

On 12/11/2015 4:33 PM, David Holmes wrote:
> webrev: http://cr.openjdk.java.net/~dholmes/8139300/webrev/
>
> Bug report is not public sorry.
>
> In the crash handler test logic in the VM we have:
>
> static void crash_with_sigfpe() {
>     // generate a native synchronous SIGFPE where possible;
>     // if that did not cause a signal (e.g. on ppc), just
>     // raise the signal.
>     volatile int x = 0;
>     volatile int y = 1/x;
>   #ifndef _WIN32
>     raise(SIGFPE);
>   #endif
>   } // end: crash_with_sigfpe
>
> and it is used here:
>
>   402     case 15: crash_with_sigfpe(); break;
>   403
>   404     default: tty->print_cr("ERROR: %d: unexpected test_num
> value.", how);
>   405   }
>   406   ShouldNotReachHere();
>
> We recently updated the compiler on OSX and started seeing occasional
> failures of the test exercising this code, the failure mode being that
> we hit the ShouldNotReachHere() at line #406.
>
> It seems the new compiler may not be generating code for the "y=1/x;"**
> so we don't get the SIGFPE and so proceed to raise it directly. That
> then hits an apparent bug on OSX where raise always sends the signal to
> the main thread not the current thread as required by POSIX in a
> multi-threaded app. Consequently raise() could return and we'd hit the
> ShouldNotReachHere().
>
> Whether the test failed or appeared to pass depended on which thread got
> into the error handler first (though I'm still unclear on the finer
> details of that potential interaction - the other thread should have
> seen error reporting was already in progress by the recursively failing
> thread!)
>
> The solution I chose is to simply convert raise(sig) into its POSIX
> specified equivalent: pthread_kill(pthreead_self(), sig);
>
> I'm a little reluctant having pthread functions in a shared file, but
> AFAIK all our platforms supports pthreads. This also doesn't seem any
> worse than assuming raise() exists on all platforms. But I could add
> some ifdef _POSIX_C_SOURCE if there is concern (and even have a #error
> for unknown platforms) ?
>
> ** I'm not surprised a compiler might elide the attempted division by
> zero. I don't think volatile on a local has any meaning and so could
> easily be optimized out completely. I overlooked that in the original
> commit of this logic, and it worked so ...
>
> Thanks,
> David