RFR(S): 8191049: Add alternate version of pns() that is callable from within hotspot source

[Thomas Stüfe]

Hi Chris,

Thank you. Yes, a comment may make sense, and/or restricting this function
to not product. Otherwise the change is fine and useful, I’ll use it
probably before long.

Thanks, Thomas

On Fri 10. Nov 2017 at 21:55, Chris Plummer <chris.plummer at oracle.com>
wrote:

> Hi Thomas,
>
> There's certainly no intent to leave in place any calls someone might add
> to pns2(). It's meant as a temporary debugging aide only. So if it were to
> fail for any reason, IMO that's no different than adding any other sort of
> temporary debugging code that could possibly crash. You fix your mistake
> and resume your debugging. If you want I can add comments that include such
> a warning.
>
> thanks,
>
> Chris
>
>
>
> On 11/10/17 12:11 AM, Thomas Stüfe wrote:
>
> Hi Chris,
>
> looks fine as a debugging aid.
>
> But it occurred to me that it may be a bit dangerous to call this from
> non-errorhandler settings. I recall seeing quite a few secondary crashes in
> VMError::print_native_stack() in hs-err files over time. Especially for
> native non-java threads. Usually this did not matter that much because
> these crashes are handled by secondary error handling when printing the
> hs-err file. But if we call it outside of error handling, we are on our own.
>
> So. IMHO, to use this functions as a debugging aid is fine, if one can
> accept a slight risk of crashing the VM. If this is not acceptable, may we
> need some more tests for this function?
>
> Kind Regards, Thomas
>
>
>
> On Thu, Nov 9, 2017 at 9:29 PM, Chris Plummer <chris.plummer at oracle.com>
> wrote:
>
>> Hi,
>>
>> Please review the following:
>>
>> https://bugs.openjdk.java.net/browse/JDK-8191049
>>
>> diff --git a/src/hotspot/share/utilities/debug.cpp
>> b/src/hotspot/share/utilities/debug.cpp
>> --- a/src/hotspot/share/utilities/debug.cpp
>> +++ b/src/hotspot/share/utilities/debug.cpp
>> @@ -631,6 +631,24 @@
>>    VMError::print_native_stack(tty, fr, t, buf, sizeof(buf));
>>  }
>>
>> +//
>> +// This version of pns() will not work when called from the debugger,
>> but is
>> +// useful when called from within hotspot code. The advantages over pns()
>> +// are not having to pass in any arguments, and it will work on
>> Windows/x64.
>> +//
>> +extern "C" void pns2() { // print native stack
>> +  Command c("pns2");
>> +  static char buf[O_BUFLEN];
>> +  if (os::platform_print_native_stack(tty, NULL, buf, sizeof(buf))) {
>> +    // We have printed the native stack in platform-specific code,
>> +    // so nothing else to do in this case.
>> +  } else {
>> +    Thread* t = Thread::current_or_null();
>> +    frame fr = os::current_frame();
>> +    VMError::print_native_stack(tty, fr, t, buf, sizeof(buf));
>> +  }
>> +}
>> +
>>  #endif // !PRODUCT
>>
>> There is also a pre-existing thread with some discussion:
>>
>>
>> http://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2017-November/025134.html
>>
>> thanks,
>>
>> Chris
>>
>>
>
>