RFR(S): 8155105: Enhance guardedMemory to detect accessing released memory

[Zhengyu Gu]

This is a debug-only change that is intended to detect accessing 
released memory, ex. double-release a malloc'd memory.

The approach is to rewrite the memory guards with "released" pattern and 
write the calling stack into user data area during os::free() call.
As the result,  verify_memory() check will result a failure if it sees 
"released" guards.

Double-free is not obvious usually, as the memory can be reallocated 
before the second free().  Most of time, it appears to be a 
wild-pointer, -XX:TraceMemoryDoubleFree flag is intended to help to 
identify such scenario, by only building released guards, but not 
actually free the memory, so it can only help when double-free is caught 
before runs out of memory.

When double-free is caught, the two free() call stacks are provided:

## nof_mallocs = 56722, nof_frees = 9099
## memory stomp:
GuardedMemory(0x00007f85a0a06c30) base_addr=0x00007f859af2f630 
tag=0x0000000000000000 user_size=17 user_data=0x00007f859af2f650
   Header guard @0x00007f859af2f630 is RELASED
   Trailer guard @0x00007f859af2f670 is RELASED
   User data appears to be releasing call stack
From:
[0x00007f859f150dc2] os::free(void*)+0x52
[0x00007f859ec79b5b] GuardedMemory::test_guarded_memory()+0x156b
[0x00007f859ed02e44] InternalVMTests::run()+0x1d4
[0x00007f859ed58c15] JNI_CreateJavaVM+0x3e5
Memory has been released from:
[0x00007f859ec79b53] GuardedMemory::test_guarded_memory()+0x1563
[0x00007f859ed02e44] InternalVMTests::run()+0x1d4
[0x00007f859ed58c15] JNI_CreateJavaVM+0x3e5
[0x00007f85a01ca753] JavaMain+0x83

Also, updated guarded memory tests to test on "base" pointer (returned 
by ::malloc()) vs "user" pointer (os::malloc()) to reflect real runtime 
scenarios.

Bug:https://bugs.openjdk.java.net/browse/JDK-8155105 
<https://bugs.openjdk.java.net/browse/JDK-8155105>
Webrev: http://cr.openjdk.java.net/~zgu/8155105/webrev/index.html 
<http://cr.openjdk.java.net/%7Ezgu/8155105/webrev/index.html>

Thanks,

-Zhengyu
<http://cr.openjdk.java.net/%7Ezgu/8155105/webrev/index.html>