8330275: Crash in XMark::follow_array

Reviewed-by: stuefe
Backport-of: 42b1d85

Author: Ashutosh Mehra

src/hotspot/cpu/aarch64/gc/x/xGlobals_aarch64.cpp

@@ -142,9 +142,11 @@
 //  * 63-48 Fixed (16-bits, always zero)
 //
 
-// Default value if probing is not implemented for a certain platform: 128TB
-static const size_t DEFAULT_MAX_ADDRESS_BIT = 47;
-// Minimum value returned, if probing fails: 64GB
+// Default value if probing is not implemented for a certain platform
+// Max address bit is restricted by implicit assumptions in the code, for instance
+// the bit layout of XForwardingEntry or Partial array entry (see XMarkStackEntry) in mark stack
+static const size_t DEFAULT_MAX_ADDRESS_BIT = 46;
+// Minimum value returned, if probing fails
 static const size_t MINIMUM_MAX_ADDRESS_BIT = 36;
 
 static size_t probe_valid_max_address_bit() {

src/hotspot/cpu/aarch64/gc/z/zAddress_aarch64.cpp

@@ -36,9 +36,11 @@
 #include <sys/mman.h>
 #endif // LINUX
 
-// Default value if probing is not implemented for a certain platform: 128TB
-static const size_t DEFAULT_MAX_ADDRESS_BIT = 47;
-// Minimum value returned, if probing fails: 64GB
+// Default value if probing is not implemented for a certain platform
+// Max address bit is restricted by implicit assumptions in the code, for instance
+// the bit layout of XForwardingEntry or Partial array entry (see XMarkStackEntry) in mark stack
+static const size_t DEFAULT_MAX_ADDRESS_BIT = 46;
+// Minimum value returned, if probing fail
 static const size_t MINIMUM_MAX_ADDRESS_BIT = 36;
 
 static size_t probe_valid_max_address_bit() {