8345273: Fix -Wzero-as-null-pointer-constant warnings in s390 code

[kimbarrett]

Please review this change to remove -Wzero-as-null-pointer-constant warnings
in s390 code.

Most places involve just changing literal 0 to nullptr.

Removed a dead return after ShouldNotReachHere() that is no longer needed.

Testing:
GHA sanity test build, with and without -Wzero-as-null-pointer-constant enabled.
I don't have the capability to run tests for this platform, so hoping someone
from the aix-ppc maintainers can do more testing.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8345273: Fix -Wzero-as-null-pointer-constant warnings in s390 code (Enhancement - P4)

Reviewers

• Julian Waters (@TheShermanTanker - Committer)
• Andrew Haley (@theRealAph - Reviewer)
• Amit Kumar (@offamitkumar - Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/22469/head:pull/22469
$ git checkout pull/22469

Update a local copy of the PR:
$ git checkout pull/22469
$ git pull https://git.openjdk.org/jdk.git pull/22469/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 22469

View PR using the GUI difftool:
$ git pr show -t 22469

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Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/22469.diff

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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:

8345273: Fix -Wzero-as-null-pointer-constant warnings in s390 code

Reviewed-by: jwaters, aph, amitkumar

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At the time when this comment was updated there had been 8 new commits pushed to the master branch:

• abcd23f: 8334756: javac crashed on call to non-existent generic method with explicit annotated type arg
• 2ddaa46: 8305010: Test vmTestbase/nsk/jvmti/scenarios/sampling/SP05/sp05t003/TestDescription.java timed out: thread not suspended
• c631719: 8343170: java/awt/Cursor/JPanelCursorTest/JPanelCursorTest.java does not show the default cursor
• 29d648c: 8341781: Improve Min/Max node identities
• 4c39e9f: 8344924: Default CA certificates loaded despite request to use custom keystore
• 0f03554: 8342469: Improve API documentation for java.lang.classfile.instruction
• 9bd70ec: 8345888: Broken links in the JDK 24 JavaDoc API documentation, build 27
• 1def2d8: 8345700: tier{1,2,3}_compiler don't cover all compiler tests

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
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[openjdk]

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[mlbridge]

Webrevs

• 02: Full - Incremental (22374e45)
• 01: Full - Incremental (dc4985cd)
• 00: Full (14501652)

[offamitkumar]

hi @kimbarrett,

I tried to build it on s390x with these changes:

diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
index 57654514eb6..ce3077e7d38 100644
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4
@@ -448,7 +448,7 @@ AC_DEFUN([FLAGS_SETUP_CFLAGS],
   CC="$CC_OLD"
   CXX="$CXX_OLD"
   CFLAGS="$CFLAGS_OLD"
-  CXXFLAGS="$CXXFLAGS_OLD"
+  CXXFLAGS="$CXXFLAGS_OLD  -Wzero-as-null-pointer-constant"
 ])

is that correct way to test it ?

I got couple of build warnings, good thing is that none of them are in s390x code. I am attaching build.log file.

build.log

[kimbarrett]

hi @kimbarrett,

I tried to build it on s390x with these changes:

diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
index 57654514eb6..ce3077e7d38 100644
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4

[snip]

is that correct way to test it ?

That's too general, affecting the entire JDK. The rule we're trying to enforce
(don't use literal 0 as a null pointer constant) is specific to HotSpot.

For testing, I've been adding the warning to the list here:

jdk/make/autoconf/flags-cflags.m4

Line 785 in e13206d

$1_WARNING_CFLAGS_JVM="-Wno-format-zero-length -Wtype-limits -Wuninitialized"

I've not verified with the build team that this is the right place ultimately.
And I suspect it's not, since your log listed warnings in adlc. I'm not seeing
any warnings there, even though (looking at the code) there clearly should be.

[TheShermanTanker]

Looks good

[TheShermanTanker]

hi @kimbarrett,
I tried to build it on s390x with these changes:

diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
index 57654514eb6..ce3077e7d38 100644
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4

[snip]

is that correct way to test it ?

That's too general, affecting the entire JDK. The rule we're trying to enforce (don't use literal 0 as a null pointer constant) is specific to HotSpot.

For testing, I've been adding the warning to the list here:

jdk/make/autoconf/flags-cflags.m4

Line 785 in e13206d

$1_WARNING_CFLAGS_JVM="-Wno-format-zero-length -Wtype-limits -Wuninitialized"

I've not verified with the build team that this is the right place ultimately. And I suspect it's not, since your log listed warnings in adlc. I'm not seeing any warnings there, even though (looking at the code) there clearly should be.

Do we also want ADLC to have nulls cleaned up? I thought it was just HotSpot that the cleanups were aimed at, not including the tools used while building it

[kimbarrett]

I've not verified with the build team that this is the right place ultimately. And I suspect it's not, since your log listed warnings in adlc. I'm not seeing any warnings there, even though (looking at the code) there clearly should be.

Do we also want ADLC to have nulls cleaned up? I thought it was just HotSpot that the cleanups were aimed at, not including the tools used while building it

That depends on whether one thinks the HotSpot Style Guide should apply to
adlc. I think it should (though I know there are violations, such as C++
Standard Library usage, that perhaps should be documented). But I'm probably
not the right person to make that call. I'll try to remember to discuss with
@vnkozlov.

I think avoiding literal 0 as a null pointer constant is generally good for
readability. Avoidance of NULL in adlc (which is not addressed here)
simplifies the proposed prevention mechanism (JDK-8343802). Otherwise we would
need to exclude the adlc source directory from the scan, and probably ensure
the adlc-generated code didn't include it either.

[kimbarrett]

I'd like a review from an s390 porter. But it's a simple enough change that I'm not going to wait indefinitely.
I'll give it another day.

[offamitkumar]

Sorry for kept you waiting. LGTM

[kimbarrett]

Thanks for reviews @theRealAph , @TheShermanTanker , and @offamitkumar

[kimbarrett]

/integrate

[openjdk]

Going to push as commit 1e9204f.
Since your change was applied there have been 10 commits pushed to the master branch:

• c40140e: 8334581: Remove no-arg constructor BasicSliderUI()
• 8de0622: 8345767: javax/swing/JSplitPane/4164779/JSplitPaneKeyboardNavigationTest.java fails in ubuntu22.04
• abcd23f: 8334756: javac crashed on call to non-existent generic method with explicit annotated type arg
• 2ddaa46: 8305010: Test vmTestbase/nsk/jvmti/scenarios/sampling/SP05/sp05t003/TestDescription.java timed out: thread not suspended
• c631719: 8343170: java/awt/Cursor/JPanelCursorTest/JPanelCursorTest.java does not show the default cursor
• 29d648c: 8341781: Improve Min/Max node identities
• 4c39e9f: 8344924: Default CA certificates loaded despite request to use custom keystore
• 0f03554: 8342469: Improve API documentation for java.lang.classfile.instruction
• 9bd70ec: 8345888: Broken links in the JDK 24 JavaDoc API documentation, build 27
• 1def2d8: 8345700: tier{1,2,3}_compiler don't cover all compiler tests

Your commit was automatically rebased without conflicts.

[openjdk]

@kimbarrett Pushed as commit 1e9204f.

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