Request for reviews (S): 6973308: Missing zero length check before repne scas in check_klass_subtype_slow_path()

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6973308/webrev

Fixed 6973308: Missing zero length check before repne scas in check_klass_subtype_slow_path()

Z flag value will not be set by repne_scan(); if RCX == 0 since
'repne' instruction does not change flags (only scas instruction
which is repeated sets flags).

Setting Z = 1 before repne_scan() in check_klass_subtype_slow_path()
will cause exception java.lang.IncompatibleClassChangeError:

      // pointer were to sneak in here.  Note that we have already loaded the
      // Klass::super_check_offset from the super_klass in the fast path,
      // so if there is a null in that register, we are already in the afterlife.
+    push(rax);
+    xorq(rax,rax); // Set Z = 1
+    pop(rax);
      repne_scanl();

% java -Xmx128M -jar GCBasher.jar -time:300
Exception in thread "main" java.lang.IncompatibleClassChangeError
         at java.lang.StringCoding$StringDecoder.decode(StringCoding.java:153)

Solution:
Instead of checking RCX for zero set Z = 0 (not equal) before 'repne'
to indicate that class was not found when RCX == 0.

Also fixed printed free stack size in hs_err files.
Added ability to abort VM only on the exception with specific message.

Tested with failed case.