Windows Debugging

Unity provides several options for debugging on Windows for forensic or live debugging of game and editor processes.

Native vs. Managed Debugging

Unity allows two types of debugging: the native C++ debugging and the C# managed debugging.

Native Debugging

Native Debugging stores symbols in pdb files for the associated binary files, such as exe and dll.

Managed Debugging

On Windows, the standard .NET managed symbols are stored in pdb files.

Symbols

Unity provides a symbol store at http://symbolserver.unity3d.com/. Much like the Microsoft’s symbol store, you can use the Unity server URL in Windows Debugger (WinDbg), or Visual Studio 2019 and later for automatic symbol resolution and downloading.

WinDbg Setup

To add a symbol store on WinDbg, use the .sympath command:

.sympath+ SRV*c:\symbols-cache*http://symbolserver.unity3d.com/

Where:

.sympath+
The + addition, leaves the existing symbol path alone, and appends this symbol store lookup.

SRV*c:\symbols-cache
The SRV indicates a remote server to fetch from, while the c:\symbols is a local path to cache the downloaded symbols and to look there first before downloading again.

*http://symbolserver.unity3d.com/
The path to the symbol store to fetch from.

Visual Studio Setup

1. Go to Tools > Options.
2. Expand the Debugging section and then select Symbols.
3. Specify a cache directory if not already specified.
4. Add a Symbol file (.pdb) location (http://symbolserver.unity3d.com/).

Live Debugging

Live Debugging is the scenario of attaching a debugger to a process that’s running normal, or to a process where an exception has been caught. For the debugger to know what’s going on, the symbols must be included in the build using the steps above. Additionally, the game executable is named according to your game name, so the debugger may have issues finding the correct pdb if it doesn’t have access to the renamed executable.

Setting up automatic exception debugging

On Windows, Microsoft sets up automatically on application crashes to go to Dr Watson/Error Reporting to Microsoft. However, if you have Visual Studio or WinDbg installed, Microsoft provides an option to instead opt to debug the crashes.
For ease of installing, follow this registry file contents to install:

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug]
"Auto"="1"
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\AeDebug]
 "Auto"="1"

Additional content for Editor debugging:

Unity.exe -dbgbreak
Will launch Unity and immediately offer a debugger to connect if the automatic crash handling is set up.

Post-Mortem/Forensic Debugging

Windows provides facilities to investigate crash dump files (.dmp or .mdmp). Depending on the type of crash dump, you might either see stack information or the entire process memory. The contents of the dump file determine the cause of the crash, which typically has at least a stack to investigate (as long as it’s a valid stack).

To investigate a dump file, you can load it up via Visual Studio or WinDbg. While Visual Studio is a more friendly tool to use, it’s slightly limited than WinDbg.

Debugging Hints and Tricks

When running Visual Studio, you can use the UnityMixedCallstack extension for VS Code by Unity that makes debugging even easier.

Managed exceptions in native land

A NullReferenceException typically looks like this:

    1b45558c()  
>   mono-2.0-bdwgc.dll!malloc(unsigned int size=12)  Line 163 + 0x5f bytes  C  
    mono-2.0-bdwgc.dll!g_hash_table_insert_replace(_GHashTable * hash=0x065c3960, void * key=0x0018cba4, void * value=0x0018cb8c, int replace=457528232)  Line 204 + 0x7 bytes  C  
    mono-2.0-bdwgc.dll!mono_jit_runtime_invoke(_MonoMethod * method=0x242bf8b0, void * obj=0x065c3960, void ** params=0x0018cba4, MonoObject * * exc=0x0018cb8c)  Line 4889 + 0xc bytes C  

Viewing managed stack frames

With the previous example again:

    1b45558c()  
>   mono-2.0-bdwgc.dll!malloc(unsigned int size=12)  Line 163 + 0x5f bytes  C  
    mono-2.0-bdwgc.dll!g_hash_table_insert_replace(_GHashTable * hash=0x065c3960, void * key=0x0018cba4, void * value=0x0018cb8c, int replace=457528232)  Line 204 + 0x7 bytes  C  
    mono-2.0-bdwgc.dll!mono_jit_runtime_invoke(_MonoMethod * method=0x242bf8b0, void * obj=0x065c3960, void ** params=0x0018cba4, MonoObject * * exc=0x0018cb8c)  Line 4889 + 0xc bytes C  

The lines without any information are managed frames. There is, however, a way to get the managed stack information: mono has a builtin function called mono_pmip, which accepts the address of a stack frame and returns a char* with information. You can invoke mono_pmip in the Visual Studio immediate window:

?(char*){,,mono-2.0-bdwgc.dll}mono_pmip((void*)0x1b45558c)
0x26a296c0 “ Tiles:OnPostRender () + 0x1e4 (1B4553A8 1B4555DC) [065C6BD0 - Unity Child Domain]”`

Note: This only works where mono-2.0-bdwgc.dll symbols are loaded properly.

Force Applications to Create Dumps

Ocassionally, the application doesn’t crash with the debugger attached, or an application crashes on a remote device where the debugger isn’t available. However, you can still get useful information if you can get the dump file - follow the below steps to do so.

Note: These instructions apply to both Windows Standalone and Universal Windows platforms when running on desktop.

1. Open the registry.
2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Windows Error Reporting.
3. Create LocalDumps folder if it’s not there.
4. Add following keys:
   • “DumpFolder”=<FolderPath goes here> , e.g., C:\Temp
   • “DumpCount”=dword:00000010
   • “DumpType”=dword:00000002
5. Launch the application via the Universal Windows PlatformAn IAP feature that supports Microsoft’s In App Purchase simulator, which allows you to test IAP purchase flows on devices before publishing your application. More info
   See in Glossary
   or Windows Standalone executable.
6. Reproduce the crash. The dump file is created in the folder you specified earlier. You can open the dump file with Visual Studio or WinDbg.