RFR: (S): JDK-8200613: SA: jstack throws UnmappedAddressException with a CDS core file

[Jini George]

Hello!

[Including runtime-dev since the changes are in runtime code]

Requesting reviews for:

Webrev: http://cr.openjdk.java.net/~jgeorge/8200613/webrev.01/
BugID: https://bugs.openjdk.java.net/browse/JDK-8200613

Issue: jhsdb jstack would throw an UnmappedAddressException with a core 
file generated from a CDS enabled java process. This is seen only with 
Linux and with G1GC, while trying to read in data from the shared 
strings region (the closed archive heap space). This region (which is a 
file backed private memory region) is not dumped into the corefile for 
Linux. This, being a heap region (and therefore being a read-write 
region) is also not read in from the classes.jsa file in SA since only 
the read only regions are read in while processing the core file. (The 
expectation being that the read write regions are in the core file).

Proposed solution: The proposed solution is to have the coredump_filter 
value corresponding to the CDS process to include bit 2 (file-backed 
private memory), so that the file-backed private memory region also gets 
dumped into the corefile. The proposed fix is in 
src/hotspot/os/linux/os_linux.cpp.

Thanks,
Jini.