8346160: Fix -Wzero-as-null-pointer-constant warnings from explicit casts

[kimbarrett]

Please review this change that removes -Wzero-as-null-pointer-constant
warnings from explicit casts of a literal 0 to a pointer type. Different
versions of gcc seem to warn about different cases changed here, but all of
these showed up as a warning in some testing, whether Oracle CI, GHA sanity
tests, or local cross-builds using Oracle's devkits for that.

Some of the changes simply replace a cast of 0 with nullptr.

The UNIX_PATH_MAX macro definitions in attachListener_{aix,posix}.cpp is
changed to use a C++11 feature for obtaining the size of a non-static data
member without requiring an instance.
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2253.html
I guess I need to propose an update to the style guide to mention this feature.

In CompressedKlassPointers::initialize, casting
CompressedClassSpaceBaseAddress to a pointer type was triggering the warning
in release builds for some reason. That's not a literal 0, even though it is
a constant 0 in a release build. Changed to avoid that cast rather than trying
to argue with some versions of the compiler.

Although different gcc versions on different platforms seemed to vary whether
warning about each of these, this actually seems to be all of the explict
casts of a literal 0 to a pointer in HotSpot. Though because of the varied
behaviors, new ones might slip in later.

Testing: mach5 tier1, GHA sanity tests, both with and without the warning enabled.

---

Progress

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Issue

• JDK-8346160: Fix -Wzero-as-null-pointer-constant warnings from explicit casts (Enhancement - P4)

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• David Holmes (@dholmes-ora - Reviewer)

Reviewing

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$ git pull https://git.openjdk.org/jdk.git pull/22740/head

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[bridgekeeper]

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[openjdk]

@kimbarrett This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8346160: Fix -Wzero-as-null-pointer-constant warnings from explicit casts

Reviewed-by: stefank, dholmes

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 16 new commits pushed to the master branch:

• ab1dbd4: 8346202: Correct typo in SQLPermission
• 6b022bb: 8344453: Test jdk/jfr/event/oldobject/TestSanityDefault.java timed out
• 3b9de11: 8319875: Add macOS implementation for jcmd System.map
• ebb27c2: 8346139: test_memset_with_concurrent_readers.cpp should not use
• c2f0ef5: 8346159: Disable CDS AOTClassLinking tests for JVMCI due to JDK-8345635
• 4b21fb9: 8343467: Remove unnecessary @SuppressWarnings annotations (security)
• e7fc0eb: 8345987: java.management has two Util.newObjectName methods (remove one)
• f647d4d: 8345936: Call ClassLoader.getResourceAsByteArray only for multi-release jar
• cfa04d3: 8346051: MemoryTest fails when Shenandoah's generational mode is enabled
• 2ce53e8: 8345970: pthread_getcpuclockid related crashes in shenandoah tests
• ... and 6 more: https://git.openjdk.org/jdk/compare/28e49e978a40f3fdff08c5e309cea739ecc870dc...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[openjdk]

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[mlbridge]

Webrevs

• 00: Full (0d6fa1c1)

[dholmes-ora]

That all seem fine. Thanks

[kimbarrett]

Thanks for reviews @stefank and @dholmes-ora

[kimbarrett]

/integrate

[openjdk]

Going to push as commit c88e081.
Since your change was applied there have been 16 commits pushed to the master branch:

• ab1dbd4: 8346202: Correct typo in SQLPermission
• 6b022bb: 8344453: Test jdk/jfr/event/oldobject/TestSanityDefault.java timed out
• 3b9de11: 8319875: Add macOS implementation for jcmd System.map
• ebb27c2: 8346139: test_memset_with_concurrent_readers.cpp should not use
• c2f0ef5: 8346159: Disable CDS AOTClassLinking tests for JVMCI due to JDK-8345635
• 4b21fb9: 8343467: Remove unnecessary @SuppressWarnings annotations (security)
• e7fc0eb: 8345987: java.management has two Util.newObjectName methods (remove one)
• f647d4d: 8345936: Call ClassLoader.getResourceAsByteArray only for multi-release jar
• cfa04d3: 8346051: MemoryTest fails when Shenandoah's generational mode is enabled
• 2ce53e8: 8345970: pthread_getcpuclockid related crashes in shenandoah tests
• ... and 6 more: https://git.openjdk.org/jdk/compare/28e49e978a40f3fdff08c5e309cea739ecc870dc...master

Your commit was automatically rebased without conflicts.

[openjdk]

@kimbarrett Pushed as commit c88e081.

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