Debugging JVM

[Aditya Mandaleeka]

Hi Manavjeet,

Like Roman, I mostly just use GDB from a terminal, but since you mentioned
that you're using VS Code as your editor and are looking for a GUI debugger,
I thought I'd mention that you can configure VS Code to debug the VM.

These links might be useful:
  https://code.visualstudio.com/docs/cpp/launch-json-reference
  https://code.visualstudio.com/docs/cpp/cpp-debug

A high-level explanation of how this works is that it will use GDB to interact
with the running process and provide views/controls that you can see in 
VS Code (so you'll get familiar GUI debugging abilities like the ability to step 
through source in your editor, set breakpoints, see local variables, see the call
stacks for each thread, etc.). And while doing this, you can also use
the integrated terminal to access any other GDB functionality that you want
to use while debugging.

I haven't used it extensively, but when I have, it has worked well (even when
used in conjunction with the Remote-SSH extension!).

Setting it up should be straightforward. Your launch.json will have your java
executable as "program", so something like 

    "program": "/home/foo/path/to/jdk/build/linux-x86_64-server-fastdebug/jdk/bin/java"

and the "args" will be a json array of whatever you want to pass to the
executable. The other settings should be self-explanatory (with the aid of
the above links). Once you have that set up, hitting the green arrow labeled
"Start Debugging" should launch your program under the debugger.

I hope that's useful and does what you're looking for.

-Aditya

-----Original Message-----
From: hotspot-gc-dev <hotspot-gc-dev-retn at openjdk.java.net> On Behalf Of Roman Kennke
Sent: Tuesday, September 22, 2020 3:06 AM
To: Manavjeet Singh <manavjeet18295 at iiitd.ac.in>; hotspot-gc-dev at openjdk.java.net
Subject: Re: Debugging JVM

Hi Manavjeet Singh,

I am using gdb to debug Hotspot. It is important to build with debug
symbols (e.g. configure with --with-native-debug-symbols=internal).
Also, it is very useful to also compile with asserts and other checks
turned on (--with-debug-level=fastdebug). If you need to step through
code, it's usually a good idea to build without optimizations too (
--with-debug-level=slowdebug).

There are GUI debuggers that may or may not be useful (e.g. I know
people who use Emacs with GDB, I am using CLion - but not for
debugging, but I think it is possible, and uses GDB as 'backend' for
that).

I hope that helps!

Best regards,
Roman

> Hi!
> I am currently learning the working of G1GC by making little changes
> in the
> code. Initially, I used GDB to add breakpoints in the code and
> understand
> its working. But I was wondering if there are any advanced GUI
> debuggers
> that can be used for this purpose? I am using VS Code as my primary
> editor.
> Can someone put light on the debugging setups they are using?
> Thanks and regards
> Manavjeet Singh
>