Windows debugging

Unity provides several options for debugging on Windows for forensic or live debugging of game and Editor processes. Unity allows two types of debugging: native C++ debugging and C# managed debugging.

• Native Debugging stores symbols in Program Database (PDB) for the associated binary files, such as exe and dll.
• On Windows, the standard .NET managed symbols are stored in PDB files with a .pdb extension.

Symbols

You can use Unity’s Symbol Store for accessing the Unity server URL in Windows Debugger (WinDbg), or Visual Studio 2019 and later for automatic symbol resolution and downloading.

Windows Debugger (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

To configure Visual Studio for debugging, follow these steps: 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, such as Unity’s Symbol Store.

Live debugging

Live debugging is the scenario of attaching a debugger to a process that’s already running, or to a process where an exception has been caught. For the debugger to spot the issue, you must include the symbols in the build using the steps described in the Visual Studio setup section. In addtion, if the game executable has the same name as your game name, the debugger might have issues finding the correct .pdb file, espectially if it doesn’t have access to the renamed executable.

Setting up automatic exception debugging

On Windows, Microsoft automatically sets up application crashes to send 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.

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 promptly 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 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 easy to use, WinDbg provids additional features, which makes it a preferred debugging tool.

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  

Managed stack frames

Managed stack frames typically resemble 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  

The lines without any information are managed frames. You can get the managed stack information in mono using its built-in 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 for debugging.

?(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, an application doesn’t crash despite having the debugger attached, or it crashes on a remote device where the debugger isn’t available. In such cases, you can get useful information from the dump file using the following steps:

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

1. Open the Windows 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 Platform 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 your preferred debugging tool, such as Visual Studio or WinDbg.