RFR(XS) 8210523 runtime/appcds/cacheObject/DifferentHeapSizes.java crash

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8210523
http://cr.openjdk.java.net/~iklam/jdk12/8210523-DifferentHeapSizes-crash.v01/

The bug is here:

    address relocated_strings_bottom = 
start_address_with_archived_oop_encoding_mode(si);
-  if (!is_aligned(relocated_strings_bottom + delta, 
HeapRegion::GrainBytes)) {
+  if (!is_aligned(relocated_strings_bottom, HeapRegion::GrainBytes)) {

relocated_strings_bottom was already relocated, so you don't need the "+ 
delta"
here. The bug was hidden because in all of our test runs, delta had been
a multiple of HeapRegion::GrainBytes, so that didn't affect the result 
of the
is_align() call.

Then, just by chance (probably due to Address Space Layout Randomization
on MacOS), we have a delta / GrainBytes == (29509025792 / 4194304.0) = 
7035.5,
so the bug is uncovered.

Thanks
- Ioi