[11u] RFR(S): 8223266: PPC64: Check for branch to illegal address before checking for mem serialization

[Gustavo Romero]

Hi,

Could the following small change be reviewed please?

Bug   : https://bugs.openjdk.java.net/browse/JDK-8223266
Webrev: http://cr.openjdk.java.net/~gromero/8223266/v1/

It fixes the JVM signal handler on Linux / PPC64 to
catch properly a SIGSEGV due to a branch to an invalid address (not mapped/not
executable) on 11u.

A similar fix [0] was already downported to 11u but it's not sufficient to cover
that case because UseMemBar feature is not obsoleted on 11u and additional code
exists for checking memory serialization in the signal handler, hence before
calling is_memory_serialization() it's necessary to check if the SIGSEGV is not
caused due to a branch to an invalid address and then only (in case SIGSEGV is
not caused due to a branch to an invalid address) call is_memory_serialization().

Thank you.

Best regards,
Gustavo

[0] https://bugs.openjdk.java.net/browse/JDK-8221834