RFR: 8361487: [ubsan] test_committed_virtualmemory.cpp check_covered_pages shows overflow [v3]

[Afshin Zafari]

> In the test,  page-numbers to be checked are passed to a checker function in which they will be changed to `-1` if they are as expected.
> Use of these `-1` values for page-numbers in consequent checks result in overflow in pointer arithmetic of `base + (-1) * page_size` which is certainly less than `base`.
> 
> The fix is to skip cases where page-number under checking is `-1`.
> Tested under UBSAN build.

Afshin Zafari has updated the pull request incrementally with one additional commit since the last revision:

  better comment

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28151/files
  - new: https://git.openjdk.org/jdk/pull/28151/files/d45208dc..f3f3fe0e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28151&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28151&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/28151.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28151/head:pull/28151

PR: https://git.openjdk.org/jdk/pull/28151