Get method name from delegate with WinDbg

Question

I have the following dump of delegate object:

Name: MyEventHandler   MethodTable: 132648fc   EEClass: 1319e2b4   Size: 32(0x20) bytes   Fields:        MT    Field   Offset                 Type VT     Attr    Value Name   790fd0f0  40000ff        4        System.Object  0 instance 014037a4 _target   7910ebc8  4000100        8 ...ection.MethodBase  0 instance 00000000 _methodBase   791016bc  4000101        c        System.IntPtr  1 instance 2ef38748 _methodPtr   791016bc  4000102       10        System.IntPtr  1 instance        0 _methodPtrAux   790fd0f0  400010c       14        System.Object  0 instance 00000000 _invocationList   791016bc  400010d       18        System.IntPtr  1 instance        0 _invocationCount   

How can I get the name of the method, pointed by the delegate?

Answer 1

In my experience the suggestion offered by hakan doesn't work. Here's what I do.

The output shows that the attached handler is a member of the object pointed to by _target. By dumping that you'll get it's method table.

I have constructed a similar example, to illustrate:

0:000> !do 02844de4  Name: System.EventHandler MethodTable: 0067afa4 EEClass: 0052ef88 Size: 32(0x20) bytes  (C:\windows\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll) Fields:       MT    Field   Offset                 Type VT     Attr    Value Name 002e6d58  40000ff        4        System.Object  0 instance 02842d20 _target 0058df70  4000100        8 ...ection.MethodBase  0 instance 00000000 _methodBase 0058743c  4000101        c        System.IntPtr  1 instance   2cc060 _methodPtr 0058743c  4000102       10        System.IntPtr  1 instance        0 _methodPtrAux 002e6d58  400010c       14        System.Object  0 instance 00000000 _invocationList 0058743c  400010d       18        System.IntPtr  1 instance        0 _invocationCount 

In this case, I'll look at the object at 02842d20.

0:000> !do 02842d20  Name: app.Foo MethodTable: 002c30bc EEClass: 002c13d4 Size: 12(0xc) bytes  (C:\workspaces\TestBench\app\bin\x86\Debug\app.exe) Fields: None 

So the target type is app.Foo. Let's dump the methods for this type.

0:000> !dumpmt -md 002c30bc EEClass: 002c13d4 Module: 002c2c5c Name: app.Foo mdToken: 02000002  (C:\workspaces\TestBench\app\bin\x86\Debug\app.exe) BaseSize: 0xc ComponentSize: 0x0 Number of IFaces in IFaceMap: 0 Slots in VTable: 6 -------------------------------------- MethodDesc Table    Entry MethodDesc      JIT Name 002ec015   002e6cbc     NONE System.Object.ToString() 002ec019   002e6cc4     NONE System.Object.Equals(System.Object) 002ec029   002e6cf4     NONE System.Object.GetHashCode() 005f4930   002e6d1c      JIT System.Object.Finalize() 005f8238   002c30b4      JIT app.Foo..ctor() 005f8270   002c30a8      JIT app.Foo.Bar(System.Object, System.EventArgs) 

Compare the values of the MethodDesc table with the original value of _methodPtr. No apparent match.

_methodPtr points to a piece of code which either does a jmp to the address of the function in question or calls a fix-up routine, so the next step is to use the !u command on the value of _methodPtr. If we see a jmp instruction, we have the address and by using !u on that, we get the method.

If, on the other hand, we see a call to clr!PrecodeFixupThunk we can get the MethodDesc by dumping the memory pointed to by _methodPtr like this

0:000> dd 2cc060  002cc060  7e5d65e8 00005e6e 002c30a8 00000000 002cc070  00000000 00000000 00000000 00000000 002cc080  00000000 00000000 00000000 00000000 

we see something that looks like a method table entry in as the third DWORD. By comparing the value 002c30a8 with the method table above, we see that the name of the method is app.Foo.Bar.

Since this is a constructed example, I know that I have found the method, I was looking for in this case.

Actually it may be bit more complicated that the above example shows, as the fields are used differently depending on the actual usage of the event. However, in my experience the approach above will work in the general publisher/subscriber scenario.

For more details on the implementation details check out the file comdelegate.cpp of the shared source CLI.

Answer 2

I believe you can use !ip2md on the value of the methodPtr. That should give the method description.