find-cbaseentity-use

name	find-CBaseEntity_Use
description	Find and identify the CBaseEntity_Use virtual function in CS2 binary using IDA Pro MCP. Use this skill when reverse engineering CS2 server.dll or server.so to locate the Use function. CBaseEntity_Use is a virtual function on CBaseEntity, resolved via vtable offset found in the function that references both "Radio.YouTakeThePoint" and "#Cstrike_TitlesTXT_Game_afk_bomb_drop". Trigger: CBaseEntity_Use, Use
disable-model-invocation	true

Find CBaseEntity_Use

Locate the CBaseEntity_Use virtual function in CS2 server binary using IDA Pro MCP tools.

Overview

CBaseEntity_Use is a virtual function on CBaseEntity. It is identified by finding the function that references both Radio.YouTakeThePoint and #Cstrike_TitlesTXT_Game_afk_bomb_drop, then locating the vtable call at the bottom of that function.

Prerequisites

• CBaseEntity vtable must already be identified (vtable YAML must exist)

If missing, run /write-vtable-as-yaml with class_name=CBaseEntity first.

Method

1. Search for Signature Strings

Use find_regex to search for both strings:

mcp__ida-pro-mcp__find_regex(pattern="Radio\\.YouTakeThePoint")
mcp__ida-pro-mcp__find_regex(pattern="#Cstrike_TitlesTXT_Game_afk_bomb_drop")

2. Find Cross-References and Identify Common Function

Use xrefs_to on both string addresses:

mcp__ida-pro-mcp__xrefs_to(addrs="<string_addr_1>")
mcp__ida-pro-mcp__xrefs_to(addrs="<string_addr_2>")

Find the function that appears in both xref results. This is the containing function (the AFK bomb drop / player use handler).

3. Decompile and Locate CBaseEntity_Use Call

Decompile the common function and look for the following code pattern near the bottom:

Windows binary:

  if ( v74 && ((*(__int64 (__fastcall **)(_QWORD *))(*v17 + <USE_OFFSET_WIN>))(v17) & 4) != 0 )
  {
    v28 = sub_XXXXXXXX(a1);
    *(_QWORD *)&v70 = sub_XXXXXXXX(a1);
    v71 = 0LL;
LABEL_117:
    v66 = *v17;
    *((_QWORD *)&v70 + 1) = v28;
    (*(void (__fastcall **)(_QWORD *, __int128 *))(v66 + <USE_OFFSET_WIN>))(v17, &v70); // CBaseEntity_Use
  }

Linux binary:

  if ( v74 && ((*(__int64 (__fastcall **)(_QWORD *))(*v17 + <USE_OFFSET_LIN>))(v17) & 4) != 0 )
  {
    v28 = sub_XXXXXXXX(a1);
    *(_QWORD *)&v70 = sub_XXXXXXXX(a1);
    v71 = 0LL;
LABEL_117:
    v66 = *v17;
    *((_QWORD *)&v70 + 1) = v28;
    (*(void (__fastcall **)(_QWORD *, __int128 *))(v66 + <USE_OFFSET_LIN>))(v17, &v70); // CBaseEntity_Use
  }

Key identification:

• The vtable call at LABEL_117 is CBaseEntity_Use
• Record the vtable offset from the call instruction (e.g. 1152 = 0x480)
• Calculate vtable index: offset / 8

4. Generate VFunc-Offset Signature

ALWAYS Use SKILL /generate-signature-for-vfuncoffset to generate a robust and unique signature for CBaseEntity_Use.

Use the instruction address of the (*(v66 + <USE_OFFSET>))(v17, &v70) call as the target instruction, and the vtable offset as the expected vfunc offset.

5. Get CBaseEntity VTable Info and Resolve Address

ALWAYS Use SKILL /get-vtable-from-yaml with class_name=CBaseEntity.

If the skill returns an error, stop and report to user. Otherwise, use vtable_entries to look up the entry at the calculated vtable index from step 3. The address at that index is CBaseEntity_Use.

6. Rename CBaseEntity_Use

Verify the function name at the resolved address. If not already renamed:

mcp__ida-pro-mcp__rename(batch={"func": {"addr": "<resolved_addr>", "name": "CBaseEntity_Use"}})

7. Write IDA Analysis Output as YAML

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

Required parameters:

• func_name: CBaseEntity_Use
• func_addr: The resolved function address from step 5
• func_sig: None (function body is too small for a unique signature)
• vfunc_sig: The validated signature from step 4

VTable parameters:

• vtable_name: CBaseEntity
• vfunc_offset: The offset from step 3
• vfunc_index: The index from step 3

Function Characteristics

• VTable Class: CBaseEntity
• Parameters: (CBaseEntity* this, CBaseEntity* activator, CBaseEntity* caller, USE_TYPE useType)
• Purpose: Called when an entity is "used" (e.g. player pressing +use on a door, button, or other interactive entity)
• Identified via: The function containing both Radio.YouTakeThePoint and #Cstrike_TitlesTXT_Game_afk_bomb_drop strings

The containing function also references:

• weapon_c4 - C4 bomb detection
• CCSPlayer_ItemServices_DropPlayerWeapon - Dropping the bomb
• Radio.YouTakeThePoint / #Cstrike_TitlesTXT_Game_afk_bomb_drop - AFK bomb drop notification

VTable Information

• VTable Name: CBaseEntity
• VTable Mangled Name:
  • Windows: ??_7CBaseEntity@@6B@
  • Linux: _ZTV11CBaseEntity
• VTable Offset: 0x480 (Windows) — may change with game updates
• VTable Index: 144 (Windows) — may change with game updates

Output YAML Format

The output YAML filename depends on the platform:

• server.dll -> CBaseEntity_Use.windows.yaml
• server.so / libserver.so -> CBaseEntity_Use.linux.yaml

Troubleshooting

If CBaseEntity vtable YAML not found:

• Run /write-vtable-as-yaml with class_name=CBaseEntity first

If the vtable offset differs from expected:

• The vtable layout may have changed in a game update
• Look for the vtable call at LABEL_117 near the bottom of the containing function
• The pattern is: check flags with & 4, then call through vtable with (v17, &v70) arguments