RFR: 8247201: Print potential pointer value of readable stack memory in hs_err file

[Stefan Karlsson]

Hi all,

Please review this patch to print potential pointer value of readable 
stack memory in hs_err files.

https://cr.openjdk.java.net/~stefank/8247201/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8247201

I often see these lines in hs_err file:
stack at sp + 2 slots: 0x00007000042e6930 points into unknown readable 
memory: 7c cb b3 05 01 00 00 00

and have to manually transpose the bytes to see if they match an 
important pointer value.

I'd like to always print the full pointer value, if possible:
stack at sp + 2 slots: 0x00007000042e6930 points into unknown readable 
memory: 0x0000000105b3cb7c | 7c cb b3 05 01 00 00 00

The suggested patch only prints this value if the dereferenced address 
is aligned, otherwise it skips it.

Side-note: the code that determines if the memory is readable only 
checks 4 bytes. So if we have a pointer at the end last few bytes of a 
page, and an inaccessible page after that, it seems like the 
pre-existing code will crash.

Thanks,
StefanK