Custom debug channel for kernel32.dll

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Julcar
Posts: 164
Joined: Thu Jul 31, 2008 8:19 pm

Custom debug channel for kernel32.dll

Post by Julcar »

Hi guys,

I would like to have a way to filter out debug log messages in kernel32.dll by setting an environment variable, just as DEBUGCHANNEL does with wine/win32ss code. I've been looking in our code but no luck, I don't know how to set the default debug channel for DEBUG_CHANNEL macro, and how they can be filtered out.

Thanks for your help guys
johnwood
Posts: 2
Joined: Mon Jul 17, 2023 4:24 pm

Re: Custom debug channel for kernel32.dll

Post by johnwood »

The ability to filter out debug log messages in `kernel32.dll` by setting an environment variable is not a built-in feature of the Windows operating system. The DEBUGCHANNEL mechanism you mentioned is specific to Wine and Win32 subsystem code, not native Windows code.

In the Windows kernel and `kernel32.dll`, the debug logging and filtering mechanisms are different. The kernel and `kernel32.dll` typically use the Windows Debugging Tools and facilities like ETW (Event Tracing for Windows) for logging and tracing purposes.

To filter debug log messages in the Windows kernel or `kernel32.dll`, you would typically need to use specialized debugging tools and techniques provided by Microsoft. These tools include WinDbg, Event Viewer, and the Windows Performance Toolkit (WPT), among others.

Here are some general steps to filter debug log messages in the Windows kernel and `kernel32.dll` using WinDbg:
  1. Install WinDbg: Download and install the Windows Debugging Tools, which includes WinDbg, from the Microsoft website (https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/).
  2. Launch WinDbg: Start WinDbg and open the target executable (such as `kernel32.dll`) or connect it to a live debugging session.
  3. Set breakpoints and configure symbols: Set breakpoints or configure symbols to allow proper debugging of the target code. This step is optional but may help in analyzing specific scenarios.
  4. Enable debug logging and filtering: Use the appropriate WinDbg commands or settings to enable debug logging and set the desired filters. For example, you can use the `.logopen` command to open a log file, `.logappend` to append to an existing log file, or `.logmask` to specify the logging level or filtering conditions.
  5. Run the target code: Execute the target code or perform the actions that trigger the debug log messages you want to filter.
  6. Analyze the log: After capturing the log, you can analyze it using WinDbg or other tools like Event Viewer or Windows Performance Analyzer. These tools allow you to search, filter, and analyze the logged messages based on various criteria.
It's important to note that debugging Windows kernel code and `kernel32.dll` is an advanced topic that requires knowledge of debugging techniques, symbols, and the Windows internals. It may not be feasible or recommended to modify or filter debug log messages in these components for typical end-user scenarios.

If you are working with a specific Windows kernel driver or a custom version of `kernel32.dll`, the implementation details may vary, and you may need to consult the relevant documentation or resources provided by Microsoft or the specific driver or library vendor.

Please ensure that you have the necessary permissions and legal rights to debug and modify Windows kernel components, as improper debugging or modification can lead to system instability or security issues.
angelaratcliffe
Posts: 3
Joined: Thu Aug 24, 2023 9:22 am

Re: Custom debug channel for kernel32.dll

Post by angelaratcliffe »

Great! This is what I am looking for
Arun1
Posts: 1
Joined: Tue Oct 24, 2023 4:28 pm
Contact:

Re: Custom debug channel for kernel32.dll

Post by Arun1 »

Julcar wrote: Fri Nov 26, 2021 11:31 am Hi guys,

I would like to have a way to filter out debug log messages in kernel32.dll by setting an environment variable, just as DEBUGCHANNEL does with wine/win32ss code. I've been looking in our code but no luck, I don't know how to set the default debug channel for DEBUG_CHANNEL macro, and how they can be filtered out.

Thanks for your help guys
Hi there,

you're on the right track, but setting the default debug channel for the DEBUG_CHANNEL macro may require some deep diving into the code. I hope someone with more expertise can chime in and help you out. Good luck!
johnsmith3321
Posts: 1
Joined: Wed Oct 25, 2023 9:38 am
Location: United States
Contact:

Re: Custom debug channel for kernel32.dll

Post by johnsmith3321 »

To filter out debug log messages in kernel32.dll by setting an environment variable, you can use the following steps:

Create a new environment variable called DEBUGCHANNEL and set its value to the debug channel that you want to filter out. For example, to filter out all debug log messages, you would set DEBUGCHANNEL to -.
Open a command prompt window and run the following command:

Code: Select all

set DEBUGCHANNEL=<debug channel>
Start your application.
All debug log messages from kernel32.dll will now be filtered out.

To set the default debug channel for the DEBUG_CHANNEL macro, you can use the following steps:

Open the kernel32.dll source code.
Find the definition of the DEBUG_CHANNEL macro.
Add the following code to the beginning of the macro definition:

Code: Select all

#ifdef DEBUGCHANNEL
#define DEBUG_CHANNEL <debug channel>
#endif
Save the kernel32.dll source code and rebuild the kernel32.dll library.
All debug log messages from kernel32.dll will now be sent to the specified debug channel.

Here is an example of how to use the DEBUGCHANNEL environment variable to filter out all debug log messages from kernel32.dll:

Code: Select all

set DEBUGCHANNEL=-
start your_application
You can also use the DEBUGCHANNEL environment variable to filter out debug log messages from other modules. For example, to filter out all debug log messages from the ntdll.dll module, you would set DEBUGCHANNEL=-:ntdll

How to filter out debug log messages by setting an environment variable

The DEBUGCHANNEL environment variable is a global variable that can be used to filter out debug log messages from any module. To filter out debug log messages from a specific module, you must set the DEBUGCHANNEL environment variable to the name of the module followed by a colon and a minus sign. For example, to filter out all debug log messages from the kernel32.dll module, you would set DEBUGCHANNEL=kernel32:-

How to set the default debug channel for the DEBUG_CHANNEL macro

The DEBUG_CHANNEL macro is a compiler macro that can be used to specify the debug channel to which debug log messages should be sent. To set the default debug channel for the DEBUG_CHANNEL macro, you must define the DEBUGCHANNEL macro in the source code of the module that is generating the debug log messages. To define the DEBUGCHANNEL macro, you must use the following syntax:

Code: Select all

#define DEBUG_CHANNEL <debug channel>
Example

The following example shows how to filter out all debug log messages from the kernel32.dll module:

Code: Select all

set DEBUGCHANNEL=-
start your_application
This will start the your_application application with all debug log messages from the kernel32.dll module filtered out.
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