find-csource2gameentities-checktransmit-and-cchecktransmitinfo

name	find-CSource2GameEntities_CheckTransmit-AND-CCheckTransmitInfo
description	Find and identify the CSource2GameEntities::CheckTransmit (virtual function) and CCheckTransmitInfo (struct) in CS2 binary using IDA Pro MCP. Use this skill when reverse engineering CS2 server.dll or server.so to locate the CSource2GameEntities::CheckTransmit function by searching for the assertion string pattern and analyzing xrefs.

Find CSource2GameEntities::CheckTransmit

Locate CSource2GameEntities::CheckTransmit in CS2 server.dll or server.so using IDA Pro MCP tools.

Method

1. Search for Assertion String

Search for the function name string in the binary:

mcp__ida-pro-mcp__find_regex pattern="CSource2GameEntities::CheckTransmit"

Expected result: A string like "CSource2GameEntities::CheckTransmit(), C:\buildworker\csgo_rel_win64\build\src\game\server\gameinterface.cpp:XXXX"

2. Find Cross-References to String

Get xrefs to the string address found in step 1:

mcp__ida-pro-mcp__xrefs_to addrs="<string_address>"

The xref should point to a function - this is CSource2GameEntities::CheckTransmit.

3. Verify Function Pattern (Optional)

Decompile the function to verify it matches the expected pattern:

mcp__ida-pro-mcp__decompile addr="<function_addr>"

Cross-Platform Identification Pattern

The function is a virtual function that handles entity transmission/visibility checks. Key characteristics:

Platform	Characteristics
Windows	References assertion string directly, complex visibility logic
Linux	Same pattern, string path differs (/build/src/game/server/gameinterface.cpp)

Common identifying features:

• References "CSource2GameEntities::CheckTransmit()" assertion string
• Part of CSource2GameEntities vtable
• Handles entity transmission/visibility checking

4. Rename the Function

mcp__ida-pro-mcp__rename batch={"func": [{"addr": "<function_addr>", "name": "CSource2GameEntities::CheckTransmit"}]}

5. Find VTable Offset and Index

ALWAYS Use SKILL /get-vtable-index to get vtable offset and index for the function.

VTable class name: CSource2GameEntities

6. Generate and Validate Unique Signature

ALWAYS Use SKILL /generate-signature-for-function to generate a robust and unique signature for the function.

7. Write IDA Analysis Output as YAML

ALWAYS Use SKILL /write-vfunc-as-yaml to write the analysis results.

Required parameters:

• func_name: CSource2GameEntities_CheckTransmit
• func_addr: The function address
• func_sig: The validated signature from step 6

VTable parameters:

• vtable_name: CSource2GameEntities
• vfunc_offset: The offset from step 5
• vfunc_index: The index from step 5

8. Look for code pattern that access CCheckTransmitInfo::m_nPlayerSlot

Look for following code pattern in CSource2GameEntities_CheckTransmit

Windows:

    do
    {
        pInfo = a2[v24];
        v36 = sub_180BC3D60(*(_DWORD *)(pInfo + 576));
        if ( !v36 || v36 != v31 )
        {
            v37 = 0LL;
            if ( v34 > 0 )
            {
            do
            {
                v38 = *(_QWORD *)pInfo;
                sub_1811957A0(*(_QWORD *)&v77[8 * v37++], &v85);
                *(_DWORD *)(v38 + 4 * ((__int64)v85 >> 5)) &= ~(1 << (v85 & 0x1F));
            }
            while ( v37 < v34 );
            v31 = v68;
            }
        }
        ++v24;
    }
    while ( v24 < v7 );

Linux:

  do
  {
    v20 = *(_QWORD *)(a2 + 8 * v19);
    v21 = sub_15CC080(*(unsigned int *)(v20 + 576));
    LOWORD(v22) = v147 & 0x7FFF;
    if ( !v21 )
      goto LABEL_33;
    v23 = (int)v162;

where a2 is CCheckTransmitInfo** ppInfoList, a3 is int infoCount

the *(int *)(v20 + 576) is CCheckTransmitInfo::m_nPlayerSlot

• The offset 576 (0x240) can change on game update.

9. Generate Struct Offset Signature and Write Struct Member YAML

For each struct member, ALWAYS generate a dedicated offset_sig first, then write a dedicated YAML file for that member.

For CCheckTransmitInfo::m_nPlayerSlot:

• Offset: 0x240 (size 4)
• Typical instruction pattern from step 8: *(unsigned int *)(v20 + 576) or *(_DWORD *)(pInfo + 576) (576 = 0x240)
• Use SKILL /generate-signature-for-structoffset with:
  • inst_addr: address of the instruction containing offset 0x240
  • struct_offset: 0x240
• Use SKILL /write-structoffset-as-yaml with:
  • struct_name: CCheckTransmitInfo
  • member_name: m_nPlayerSlot
  • offset: 0x240
  • size: 4
  • offset_sig: validated signature from /generate-signature-for-structoffset

Function Characteristics

• VTable Index: ~12 (may vary by platform and game version)
• VTable Offset: ~0x60 (may vary by platform and game version)
• Parameters: (this, ...) - handles entity transmission checks
• Purpose: Determines which entities should be transmitted to clients based on visibility and other criteria

Platform Differences

Aspect	Windows	Linux
String path	C:\buildworker\csgo_rel_win64\...	/build/src/game/server/...
VTable index	~12	May differ slightly

Output YAML Format

The output YAML filename depends on the platform:

• server.dll → CSource2GameEntities_CheckTransmit.windows.yaml, CCheckTransmitInfo_m_nPlayerSlot.windows.yaml
• server.so → CSource2GameEntities_CheckTransmit.linux.yaml, CCheckTransmitInfo_m_nPlayerSlot.linux.yaml