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debugging.md

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Debugging WSL

Logging

There are multiple sources of logging in WSL. The main one is the ETL trace that is emitted from Windows processes.

To collect an ETL trace, run (link to wsl.wprp):

wpr -start wsl.wprp -filemode

[reproduce the issue]

wpr -stop logs.ETL

The consolidated wsl.wprp file includes multiple profiles for different scenarios:

  • WSL - General WSL tracing (default)
  • WSL-Storage - Enhanced storage tracing
  • WSL-Networking - Comprehensive networking tracing
  • WSL-HvSocket - HvSocket-specific tracing

To use a specific profile, append !ProfileName to the wprp file, e.g., wpr -start wsl.wprp!WSL-Networking -filemode

Once the log file is saved, you can use WPA to view the logs.

Notable ETL providers:

  • Microsoft.Windows.Lxss.Manager: Logs emitted from wslservice.exe Important events:

    • GuestLog: Logs from the vm's dmesg
    • Error: Unexpected errors
    • CreateVmBegin, CreateVmEnd: Virtual machine lifetime
    • CreateNetworkBegin, CreateNetworkEnd: Networking configuration
    • SentMessage, ReceivedMessage: Communication on the hvsocket channels with Linux.

  • Microsoft.Windows.Subsystem.Lxss: Other WSL executables (wsl.exe, wslg.exe, wslconfig.exe, wslrelay.exe, ...) Important events:

    • UserVisibleError: An error was displayed to the user

  • Microsoft.Windows.Plan9.Server: Logs from the Windows plan9 server (used when accessing /mnt/ shares and running Windows)

On the Linux side, the easiest way to access logs is to look at dmesg or use the debug console, which can enabled by writing:

[wsl2]
debugConsole=true

to %USERPROFILE%/.wslconfig and restarting WSL

Attaching debuggers

Usermode can be attached to WSL Windows processes (wsl.exe, wslservice.exe, wslrelay.exe, ...). The symbols are available under the bin/<platform>/<target> folder. You can also use this trick to automatically collect crash dumps when processes crash.

Linux debugging

gdb can be attached to Linux processes (see man gdb).

The simplest way to debug a WSL process with gdb is to use the /mnt mountpoints to access the code from gdb. Once started, just use dir /path/to/wsl/source in gdb to connect the source files.

Root namespace debugging

Some WSL process such as gns or mini_init aren't accessible from within WSL distributions. To attach a debugger to those, use the debug shell via:

wsl --debug-shell

You can then install gdb by running tdnf install gdb and start debugging processes.