RFR: 8352098: -Xrunjdwp fails on static JDK

[David Holmes]

On Mon, 17 Mar 2025 19:37:48 GMT, Jiangli Zhou <jiangli at openjdk.org> wrote:

> Please review this fix that avoids `JvmtiAgent::convert_xrun_agent` from prematurely exiting VM if `lookup_On_Load_entry_point` cannot load the agent using `JVM_OnLoad` symbol. Thanks
> 
> `lookup_On_Load_entry_point` first tries to load the builtin agent from the executable by checking the requested symbol (`JVM_OnLoad`). If no builtin agent is found, it then tries to load the agent shared library (e.g. `libjdwp.so`) by calling `load_library`. The issue is that `load_library` is called with `vm_exit_on_error` set to `true`, which causes the VM to exit immediately if the agent shared library is not loaded. Therefore, `JvmtiAgent::convert_xrun_agent` has no chance to try loading the agent using `Agent_OnLoad` symbol (https://github.com/openjdk/jdk/blob/19154f7af34bf6f13d61d7a9f05d6277964845d8/src/hotspot/share/prims/jvmtiAgent.cpp#L352). This is a hidden issue on regular JDK, since the `load_library` can successfully find the agent shared library when `JvmtiAgent::convert_xrun_agent` first tries to load the agent using `JVM_OnLoad` symbol. The issue is noticed on static JDK as there is no `libjdwp.so` in static JDK. It can be reproduced with jtreg `runtime/6294277/Sou
 rceDebugExtension.java` test.
> 
> As part of the fix, I cleaned up following in `invoke_JVM_OnLoad` and `invoke_Agent_OnLoad`. If there's an error, the VM should already have exited during `lookup_<JVM|Agent>_OnLoad_entry_point` in those cases.
> 
> 
>   if (on_load_entry == nullptr) {
>     vm_exit_during_initialization("Could not find ... function in -Xrun library", agent->name());
>   }

This seems reasonable to me. A couple of nits.

Thanks

src/hotspot/share/prims/jvmtiAgent.cpp line 360:

> 358:   // to try lookup_Agent_OnLoad_entry_point for Agent_OnLoad as well.
> 359:   OnLoadEntry_t on_load_entry = lookup_JVM_OnLoad_entry_point(
> 360:     this, /* vm exit on error */ false);

Suggestion:

  OnLoadEntry_t on_load_entry = lookup_JVM_OnLoad_entry_point(this, /* vm exit on error */ false);

src/hotspot/share/prims/jvmtiAgent.cpp line 365:

> 363:   if (on_load_entry == nullptr) {
> 364:     on_load_entry = lookup_Agent_OnLoad_entry_point(
> 365:       this, /* vm exit on error */ true);

Suggestion:

    on_load_entry = lookup_Agent_OnLoad_entry_point(this, /* vm exit on error */ true);

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

Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/24086#pullrequestreview-2692846277
PR Review Comment: https://git.openjdk.org/jdk/pull/24086#discussion_r2000148624
PR Review Comment: https://git.openjdk.org/jdk/pull/24086#discussion_r2000148978