RFR: 8359472: JVM crashes when attaching a dynamic agent before JVMTI_PHASE_LIVE [v2]

[David Holmes]

On Tue, 14 Oct 2025 08:17:19 GMT, Francesco Andreuzzi <fandreuzzi at openjdk.org> wrote:

>> In this PR I add a check to prevent debug builds to crash when an agent tries to attach while the JVM is not in live phase.
>> 
>> Passes tier1 and tier2 (fastdebug).
>
> Francesco Andreuzzi has updated the pull request incrementally with one additional commit since the last revision:
> 
>   summary

Generally looks good. Not 100% sure on the test structure but serviceability folk can chime in there if needed.

Suggestion:

diff --git a/src/jdk.jcmd/share/man/jcmd.md b/src/jdk.jcmd/share/man/jcmd.md
index 4e67e7a4502..69784050984 100644
--- a/src/jdk.jcmd/share/man/jcmd.md
+++ b/src/jdk.jcmd/share/man/jcmd.md
@@ -551,7 +551,7 @@ ## Commands for jcmd
     events, use `JFR.view all-events`.
 
 `JVMTI.agent_load` [*arguments*]
-:   Loads JVMTI native agent.
+:   Loads JVMTI native agent. (Live phase only)
 
     Impact: Low

src/hotspot/share/prims/jvmtiAgentList.cpp line 200:

> 198:                                 const char* options, outputStream* st) {
> 199:   if (JvmtiEnvBase::get_phase() != JVMTI_PHASE_LIVE) {
> 200:     st->print_cr("Not in live phase");

Suggestion:

    st->print_cr("Dynamic agent loading is only permitted in the live phase");

test/hotspot/jtreg/serviceability/EarlyDynamicLoad/TestEarlyDynamicLoadJcmd.java line 45:

> 43:                 "-agentpath:" + Utils.TEST_NATIVE_PATH + File.separator + System.mapLibraryName("EarlyDynamicLoad"),
> 44:                 "-version");
> 45:         pb.environment().put("MODE", "jcmd");

This env-var seems unused

test/hotspot/jtreg/serviceability/EarlyDynamicLoad/TestEarlyDynamicLoadJcmd.java line 50:

> 48: 
> 49:         OutputAnalyzer output = new OutputAnalyzer(pb.start());
> 50:         output.shouldHaveExitValue(0);

Yes but more importantly we should be checking for the "not in live phase" error message.

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

Changes requested by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27766#pullrequestreview-3343557488
PR Review Comment: https://git.openjdk.org/jdk/pull/27766#discussion_r2434967688
PR Review Comment: https://git.openjdk.org/jdk/pull/27766#discussion_r2435031512
PR Review Comment: https://git.openjdk.org/jdk/pull/27766#discussion_r2435035321