How can I step into JNI .c files from my .java robot code?

[cwm9cwm9]

I have FRC robot code, and I would like to step in to WPILIB .c JNI files (e.g. while simulating the robot code. Is there a way to do this? I am in MS Code on Windows. Thanks.

[ThadHouse]

Vscode does not support mixed mode debugging. The only way to do this is to attach 2 different debuggers, one to the Java code and 1 to the c++ code. The best one for doing that on windows is WinDbg on the windows store. You can then set breakpoints in the native code that can get hit when Java calls into them.

[cwm9cwm9]

Thanks! Can you give me a little hint on how to get there?

I see there are sources available in the various files located at C:\Users\Public\wpilib\2024\maven\edu\wpi\first[component][component]-cpp\2024.3.2[component]-sources.zip

I see that there are debug versions of the libraries in files named [component]-cpp-2024.3.2-windowsx86-64debug.zip

I didn't see an obvious way in the settings.grade file to switch to the debug versions, so I simply extracted the files to [project]\build\jni\debug, then renamed release to realrelease and debug to release.

I tried to do pdbstr.exe -r -p:wpiHaljni.pdb -s:srcsrv in order to figure out what source folder the pdb's are trying to use, but nothing was returned despite using the "debug" versions of the DLLs and PDBs.

In my launch.json I have added:

{
  "name": "C++ Debug (Attach)",
  "type": "cppdbg",
  "request": "attach",
  "program": "C:\\Program Files\\Amazon Corretto\\jdk17.0.1_12\\bin\\java.exe",
  "processId": "${command:pickProcess}",
  "MIMode": "cdb",
  "miDebuggerPath": "C:\\Program Files (x86)\\Windows Kits\\10\\Debuggers\\x64\\cdb.exe",
  "sourceFileMap": {
    "": "D:\\Repos\\wpilibsuite\\hal\\src\\main\\native\\cpp\\jni" 
  }
}

but it's unclear what I should use in the source file map, or where I should put the source files themselves... (Do I need to put them in my project somewhere?)

Alternatively, do I need to completely rebuild the WPILIB files in order to use some other IDE and debugger?

Thanks for anything you can do to point me in the right direction!

[ThadHouse]

You don't want to just rename the debug files. You instead to just add wpi.java.debugJni = true to your build.gradle project, which will make it use the debug JNI files automatically.

And then sources are a real PITA to get working in VS Code. Really recommend you use WinDbg Preview from the windows store. That will actually use a feature in the PDB that lets it load source files from GitHub. VS Code does not support that functionality. You can just attach WinDbg to the java executable, and that should load all the PDBs for the WPILib Libraries when they get loaded.

[cwm9cwm9]

Oh, I see! I didn't realize you meant WinDbg was an actual product. I mean, you said it, it just kind of went over my head. I installed and see there's an option to "Change Use Windbg Preview (From Store) As Windows Debugger", so I'm trying that now. Thank you for the help!