Request for review: 7034585 Adjust fillinStackTrace filtering to assist 6998871

[David Holmes]

webrev:

http://cr.openjdk.java.net/~dholmes/7034585/webrev/

When an exception is created, fillInStacktrace is called to populate the 
backtrace information. This is done in 
java_lang_Throwable::fill_in_stack_trace in the VM. Because the 
interesting part of the stacktrace is from the location where the 
exception was created, and upwards, filtering is applied in 
fill_in_stack_trace to remove the entry for fillInStackTrace() itself, 
and the exception constructors.

The current filtering code only expects to find a single frame for the 
fillInStackTrace method, so if an exception class overrides 
fillInStackTrace (and invokes super.fillInStackTrace) this actually 
disables the filtering of the constructors. Eg we see:

Exception in thread "main" MyException
         at MyException.fillInStackTrace(MyException.java:3)
         at java.lang.Throwable.<init>(Throwable.java:260)
         at java.lang.Exception.<init>(Exception.java:54)
         at java.lang.RuntimeException.<init>(RuntimeException.java:51)
         at MyException.<init>(MyException.java:1)
         at MyException.main(MyException.java:7)

instead of:

Exception in thread "main" MyException
         at MyException.main(MyException.java:7)

The changes to Throwable.java for 6998871 effectively introduce an 
additional fillInStackTrace() frame and so this too disables the desired 
filtering of the backtrace.

The proposal is quite simple: to modify fill_in_stack_trace so that it 
expects one or more fillInStackTrace frames, followed by zero or more 
constructor frames. This addresses the needs of 6998871 as well as 
fixing any user-defined overriding of fillInStackTrace.

Thanks,
David