To diagnose which DLL is unable to be loaded by a subject DLL, especially in a .NET context, you can utilize several tools and methods:
Dependency Walker
**Tool**: Dependency Walker (depends.exe)
**Usage**: This tool analyzes the dependencies of a DLL and can help you see which DLLs are missing or failing to load. It provides a detailed tree view of all dependencies, showing the status of each one.
**Steps**:
Download Dependency Walker from [dependencywalker.com](http://www.dependencywalker.com/).
Open your subject DLL with Dependency Walker.
Check for any missing or red-colored entries in the tree.
Process Monitor (ProcMon)
**Tool**: Process Monitor (part of Sysinternals Suite)
**Usage**: ProcMon allows you to capture real-time file system, registry, and process/thread activity. This can help you see which DLLs are being accessed and which ones are failing to load.
**Steps**:
Download and run Process Monitor from [Microsoft Sysinternals](https://docs.microsoft.com/en-us/sysinternals/downloads/procmon).
Set a filter for your application (use the process name).
Look for "NAME NOT FOUND" or "DLL NOT FOUND" events, which indicate that a specific DLL could not be loaded.
3. **Fusion Log Viewer**
**Tool**: Fusion Log Viewer (Fuslogvw.exe)
**Usage**: This tool logs assembly binding failures, which can be particularly useful for .NET applications to determine why a specific assembly (DLL) failed to load.
**Steps**:
Open the Developer Command Prompt for Visual Studio.
Run `fuslogvw.exe`.
Enable logging and reproduce the issue.
Check the logs for any binding errors or issues related to your subject DLL.
4. **.NET Assembly Binding Logging**
If the subject DLL is a .NET assembly, you can enable assembly binding logging in the registry:
**Steps**:
Open `regedit`.
Navigate to `HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fusion`.
Create a new DWORD value named `ForceLog` and set it to `1`.
Create a new DWORD value named `LogPath` and set it to a directory where you want the logs saved.
Reproduce the issue, and check the logs in the specified directory.
5. **Debugging with Visual Studio**
If you have the source code for the .NET application, you can attach the debugger to your application and set breakpoints around the P/Invoke calls.
Check for exceptions thrown during the load process. The exception messages can often provide insight into what went wrong.
*Using LoadLibraryE
