RFR: 8306561: Gtests crash with SIGSEGV in print_pointer_information on AIX

[Thomas Obermeier]

MallocTracker::print_pointer_information in src/hotspot/share/services/mallocTracker.cpp is called to check the highest pointer address of the reserved region. To do so it aligns the test pointer down to the next 8 Byte boundary and casts this address to class MallocHeader in order to use this classes eye-catcher member _canary for validation. Method looks_valid() dereferences _canary's content. _canary has an offset of 14 bytes relative to the class. Therefore it resides outside the reserved region for the highest pointer address, which causes a segmentation violation.

We would expect the same error also for other platforms than AIX as memory is read, which is not allocated. Interestingly, Linux seems to allow this access for 5 times 4K above the reserved region.

As a solution, looks_valid() should check _canary's address as being invalid, and return false immediately.

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Commit messages:
 - 8306561: copyright and problem listing
 - JDK-8306561: test canary

Changes: https://git.openjdk.org/jdk/pull/16381/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16381&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306561
  Stats: 9 lines in 2 files changed: 5 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16381.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16381/head:pull/16381

PR: https://git.openjdk.org/jdk/pull/16381