8366154: Validate thread type requirements in debug commands #27033

krk · 2025-09-01T11:36:21Z

Prevents segmentation faults during gdb sessions. The crashes were caused by the ResourceMark constructor being called on a native thread, which is not supported. This happened when invoking debug commands that require a Thread or JavaThread context from an incorrect thread type.

Solution

This change introduces onThread() and onJavaThread() helper methods to the Command class. These methods validate the thread context and ensure ResourceMark is only created when on a valid VM thread. All thread-dependent debug commands now use these guards to validate the context, printing a clear error and exiting gracefully upon failure.

Testing

Manually verified using gdb by calling the modified commands (ps, universe, pns, etc.) from different thread contexts (native, Java, and non-java threads) to ensure they fail gracefully with an error message instead of crashing the debug session.

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-8366154: Validate thread type requirements in debug commands (Bug - P4)

Reviewers

David Holmes (@dholmes-ora - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/27033/head:pull/27033
$ git checkout pull/27033

Update a local copy of the PR:
$ git checkout pull/27033
$ git pull https://git.openjdk.org/jdk.git pull/27033/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 27033

View PR using the GUI difftool:
$ git pr show -t 27033

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/27033.diff

Using Webrev

Link to Webrev Comment

Prevent crashes when calling interactive debug commands from native or non-java threads. Add onThread() and onJavaThread() methods to the Command class to validate the current thread type. Update debug commands to use these checks, printing an error and exiting gracefully upon failure.

bridgekeeper · 2025-09-01T11:37:07Z

👋 Welcome back krk! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-09-01T11:37:53Z

@krk 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:

8366154: Validate thread type requirements in debug commands

Reviewed-by: 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 74 new commits pushed to the master branch:

a03302d: 8366434: THP not working properly with G1 after JDK-8345655
62bc7b7: 8300080: offset_of for GCC/Clang exhibits undefined behavior and is not always a compile-time constant
90a2db1: 8366474: Rename MetaspaceObj::is_shared() to MetaspaceObj::in_aot_cache()
... and 71 more: https://git.openjdk.org/jdk/compare/849570a94a3178da7899e5cd36400ef03ad9ae29...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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@dholmes-ora) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

openjdk · 2025-09-01T11:38:43Z

@krk The following label will be automatically applied to this pull request:

hotspot

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

src/hotspot/share/utilities/debug.cpp

Co-authored-by: Francesco Andreuzzi <[email protected]>

mlbridge · 2025-09-01T11:42:16Z

Webrevs

01: Full - Incremental (0d3ded95)
00: Full (74d1e08b)

dholmes-ora

We typically assume the user knows what they are doing at this level, but I suppose making it a little more robust doesn't hurt. I don't think we quite need everything though.

Thanks

dholmes-ora · 2025-09-01T21:47:27Z

src/hotspot/share/utilities/debug.cpp

+    }
+
+    if (!_has_rm) {
+      ::new (&_rm) ResourceMark();


There should be #include <new> to use global placement-new.

added, thanks.

dholmes-ora · 2025-09-01T21:54:13Z

src/hotspot/share/utilities/debug.cpp

+  bool onJavaThread() {
+    if (!onThread()) return false;
+
+    if (JavaThread::active() == nullptr) {
+      tty->print_cr("Failed: Current thread is not a java thread or the vm thread");
+      return false;
+    }
+    return true;
+  }


I don't think we need this. The commands that require a JavaThread should be checking that directly themselves. Typically we assume/expect the person debugging to know what they are dealing with and use the appropriate commands.

I will remove this function and do the check in the 3 call sites of it.

@dholmes-ora, are you sure you want this level of code duplication? As is it, the latest version duplicates the following 3 times

if (!c.onThread()) return; JavaThread* p = JavaThread::active(); if (p == nullptr) { tty->print_cr("Failed: JavaThread::active is null"); return; } tty->print(" for thread: "); p->print(); tty->cr();

dholmes-ora · 2025-09-01T21:58:02Z

src/hotspot/share/utilities/debug.cpp

+      return false;
+    }
+
+    if (!_has_rm) {


Is it even possible for this not to be false with correct usage?

No, onThread would have to be called at least twice.

dholmes-ora

This seems okay to me.

Note you need two reviews before integrating.

openjdk bot added the hotspot [email protected] label Sep 1, 2025

fandreuz reviewed Sep 1, 2025

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src/hotspot/share/utilities/debug.cpp Outdated Show resolved Hide resolved

openjdk bot added the rfr Pull request is ready for review label Sep 1, 2025

Update src/hotspot/share/utilities/debug.cpp

74d1e08

Co-authored-by: Francesco Andreuzzi <[email protected]>

dholmes-ora suggested changes Sep 1, 2025

View reviewed changes

krk added 2 commits September 2, 2025 11:05

remove onJavaThread and check JavaThread::active null where needed

0f627f9

add include for global placement new

0d3ded9

dholmes-ora approved these changes Sep 4, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Sep 4, 2025

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