gdb and OpenJDK

[Volker Simonis]

Hi Jeremy,

nice to see that somebody is working on this topic.

Can you please detail a little bit on how this would work?
As far as I understand you extend gdb to support "frame undwinder"
plugins written in Python.

One of these plugins, which you want to contribute to the OpenJDK, can
be used to unwind native Java/HotSpot stack frames by calling out to
the serviceability agent. Can you please explain how this could work?
If you debug a Java process with gdb, gdb attaches to that process
using "ptrace". The SA agent uses "ptrace" as well but as far as I
know, only once process can attach to another process at the same
time. So how is this callback from gdb to the SA agent supposed to
work?

Regards,
Volker


On Wed, Feb 11, 2015 at 11:27 PM, Jeremy Manson <jeremymanson at google.com> wrote:
> Hey folks,
>
> I think I've mentioned to some of the people on this list that we (and by
> we, I mean Sasha Smundak) have been working on interoperability between gdb
> and Java.  Basically, what we have now allows us to get a backtrace in gdb
> that includes Java frames with parameter values (no local variables yet).
>
> Needless to say, this has been terribly, terribly helpful in our JVM and JNI
> debugging.
>
> Support for this feature is basically two parts:
>
> First, gdb needed to be extended to support the ability to plug in a frame
> unwinder.  The process of submitting this to gdb (which has been ongoing for
> quite a while) is finally starting to make reasonable progress.
>
> Next, we need a plugin for OpenJDK.  We have a plugin written that calls out
> to the serviceability agent.  (It's written in Python, per gdb's
> requirements).
>
> Pending the gdb support being finalized, we'd love to contribute the plugin
> to OpenJDK.    What should we do make that happen?  Write a JEP and submit
> it to this list?  Technically, neither of us are committers (which you need
> to be to submit a JEP), but I imagine we can work around that.
>
> Here's the gdb patch, for anyone interested:
>
> https://sourceware.org/ml/gdb-patches/2014-12/msg00408.html
>
> Thanks!
>
> Jeremy