Hook ProcessEvent

[rkr35]

I believe the following is the beginning of ProcessEvent:

0115D9F0 | 55 | push ebp |
0115D9F1 | 8BEC | mov ebp,esp |
0115D9F3 | 6A FF | push FFFFFFFF |
0115D9F5 | 68 B8E4FD01 | push borderlandspresequel.1FDE4B8 |  
0115D9FA | 64:A1 00000000 | mov eax,dword ptr fs:[0] |  
0115DA00 | 50 | push eax |  
0115DA01 | 83EC 50 | sub esp,50 |  
0115DA04 | A1 E0834902 | mov eax,dword ptr ds:[24983E0] |  
0115DA09 | 33C5 | xor eax,ebp |  
0115DA0B | 8945 F0 | mov dword ptr ss:[ebp-10],eax |  
0115DA0E | 53 | push ebx |  
0115DA0F | 56 | push esi |  
0115DA10 | 57 | push edi |  
0115DA11 | 50 | push eax |  
0115DA12 | 8D45 F4 | lea eax,dword ptr ss:[ebp-C] |  
0115DA15 | 64:A3 00000000 | mov dword ptr fs:[0],eax |  
0115DA1B | 8BF1 | mov esi,ecx |  
0115DA1D | 8975 EC | mov dword ptr ss:[ebp-14],esi |  
0115DA20 | 8B7D 08 | mov edi,dword ptr ss:[ebp+8] |  
0115DA23 | F787 80000000 02040000 | test dword ptr ds:[edi+80],402 |  

And here's one of the call sites:

mov esi,dword ptr ds:[ebx] ; Get pointer to first vtable entry of UObject.
push 0
lea edx,dword ptr ss:[ebp+8]
push edx
push 0
push eax
push ecx
mov ecx,ebx
movss dword ptr ss:[ebp+8],xmm0
call borderlandspresequel.10A0920
mov edx,dword ptr ds:[esi+E8] ; Index into vtable to get address of ProcessEvent
push eax
mov ecx,ebx ; ecx = ebx = this pointer = UObject we're calling ProcessEvent on
call edx ; Call ProcessEvent

The [esi+E8] suggests that the vtable index for ProcessEvent is 0xE8 / 4 = 58.

I'm assuming our detoured function will need to use the fastcall calling convention and ignore edx as the second parameter since Rust doesn't have a stable thiscall calling convention I could use in this scenario. Otherwise, I'm not sure how we would access the this pointer (which is the UObject that is calling ProcessEvent as a member function) that the game will store in ecx.