# Write Vtable As YAML

> Write vtable analysis results as YAML file beside the binary using IDA Pro MCP. Use this skill after locating a vtable to persist the results in a standardized YAML format.

- Skill: `hlnd2t/write-vtable-as-yaml` (Agent Skill)
- Install (CLI): `npx skillmds@latest add hlnd2t/write-vtable-as-yaml`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hlnd2t/write-vtable-as-yaml/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: HLND2T (https://skillmd.com/u/hlnd2t)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/hlnd2t/write-vtable-as-yaml

---


# Write VTable as YAML

Persist vtable analysis results to a YAML file beside the binary using IDA Pro MCP.

## Prerequisites

Before using this skill, you should have:
1. Located the target vtable address
2. Identified the class name for the vtable

## Required Parameters

| Parameter | Description | Example |
|-----------|-------------|---------|
| `vtable_class` | Class name for the vtable | `CSource2Server` |
| `vtable_va` | Virtual address of the vtable | `0x182B8D9D8` |

## Optional Parameters

| Parameter | Description | Example |
|-----------|-------------|---------|
| `vtable_symbol` | The IDA symbol name for the vtable | "??_7CBaseEntity@@6B@" |

## Method

```python
mcp__ida-pro-mcp__py_eval code="""
import idaapi
import ida_bytes
import ida_name
import os
import yaml

# === REQUIRED: Replace these values ===
vtable_class = "<vtable_class>"     # e.g., "CBaseEntity"
vtable_va = <vtable_va>             # e.g., 0x182B8D9D8
# ======================================

# === OPTIONAL: Replace these values ===
vtable_symbol = "<vtable_symbol>"     # e.g., "??_7CBaseEntity@@6B@" or "_ZTV11CBaseEntity + 0x10" or "off_180XXXXXX"
# ======================================

input_file = idaapi.get_input_file_path()
dir_path = os.environ.get('CS2VIBE_ARTIFACT_DIR') or os.path.dirname(input_file)

if input_file.endswith('.dll'):
    platform = 'windows'
    image_base = idaapi.get_imagebase()
else:
    platform = 'linux'
    image_base = 0x0

vtable_rva = vtable_va - image_base

# Handle Linux vtables (skip RTTI metadata)
vtable_name = ida_name.get_name(vtable_va) or ""
if vtable_name.startswith("_ZTV"):
    vtable_va = vtable_va + 0x10
    vtable_rva = vtable_va - image_base

# Determine pointer size and count virtual functions
ptr_size = 8 if idaapi.inf_is_64bit() else 4
vtable_entries = []

for i in range(1000):
    if ptr_size == 8:
        ptr_value = ida_bytes.get_qword(vtable_va + i * ptr_size)
    else:
        ptr_value = ida_bytes.get_dword(vtable_va + i * ptr_size)

    if ptr_value == 0 or ptr_value == 0xFFFFFFFFFFFFFFFF:
        break

    func = idaapi.get_func(ptr_value)
    if func is None:
        flags = ida_bytes.get_full_flags(ptr_value)
        if not ida_bytes.is_code(flags):
            break

    vtable_entries.append(ptr_value)

count = len(vtable_entries)
vtable_size = count * ptr_size

# Build YAML data structure
yaml_data = {
    'vtable_class': vtable_class,
    'vtable_symbol': vtable_symbol,
    'vtable_va': hex(vtable_va),
    'vtable_rva': hex(vtable_rva),
    'vtable_size': hex(vtable_size),
    'vtable_numvfunc': count,
    'vtable_entries': {i: hex(entry) for i, entry in enumerate(vtable_entries)}
}

yaml_path = os.path.join(dir_path, f"{vtable_class}_vtable.{platform}.yaml")
with open(yaml_path, 'w', encoding='utf-8') as f:
    yaml.dump(yaml_data, f, default_flow_style=False, sort_keys=False, allow_unicode=True)
print(f"Written to: {yaml_path}")
"""
```

## Output File Naming Convention

The output YAML filename follows this pattern:
- `<vtable_class>_vtable.<platform>.yaml`

Examples:
- `server.dll` → `CSource2Server_vtable.windows.yaml`
- `libserver.so` / `libserver.so` → `CSource2Server_vtable.linux.yaml`

## Output YAML Format

`CSource2Server_vtable.windows.yaml` - Example for CSource2Server vtable on Windows:

```yaml
vtable_class: CSource2Server
vtable_symbol: off_180XXXXXX # Symbol in IDA to CSource2Server's vtable
vtable_va: 0x182B8D9D8       # Virtual address - changes with game updates
vtable_rva: 0x2B8D9D8        # Relative virtual address (VA - image base) - changes with game updates
vtable_size: 0x2D8           # VTable size in bytes - changes with game updates
vtable_numvfunc: 97          # Number of virtual functions - changes with game updates
vtable_entries:              # Every virtual functions starting from vtable[0]
  0: 0x180C87B20             # vtable[0] - changes with game updates
  1: 0x180C87FA0             # vtable[1] - changes with game updates
  2: 0x180C87FF0             # vtable[2] - changes with game updates
```

`CSource2Server_vtable.linux.yaml` - Example for CSource2Server vtable on linux:

```yaml
vtable_class: CSource2Server
vtable_symbol: _ZTV14CSource2Server + 0x10 # Symbol in IDA to CSource2Server's vtable
vtable_va: '0x2261dd8'       # Virtual address - changes with game updates
vtable_rva: '0x2261dd8'      # Relative virtual address (VA - image base) - changes with game updates
vtable_size: '0x310'         # VTable size in bytes - changes with game updates
vtable_numvfunc: 98          # Number of virtual functions - changes with game updates
vtable_entries:              # Every virtual functions starting from vtable[0]
  0: '0x16ea780'             # vtable[0] - changes with game updates
  1: '0x16e9b50'             # vtable[1] - changes with game updates
  2: '0x16e3270'             # vtable[2] - changes with game updates
```

## Platform Detection

The skill automatically detects the platform based on file extension:
- `.dll` → Windows (uses `idaapi.get_imagebase()` for image base)
- `.so` → Linux (uses `0x0` as image base, skips RTTI metadata for `_ZTV` prefixed vtables)

## Linux VTable Handling

For Linux binaries, vtables with `_ZTV` prefix (mangled vtable names) have RTTI metadata at the beginning:
- Offset 0x00: offset to top
- Offset 0x08: RTTI pointer
- Offset 0x10: First virtual function pointer

The skill automatically skips this metadata when counting virtual functions.

## Trusted finalization

This writer produces a semantic YAML payload at the caller-provided expected artifact path. It does not own final field ordering, scalar spelling, encoding, or line endings. After runtime validation, the trusted analyzer rewrites every successful preprocessor or Agent output through the Source2 central canonicalizer; that canonical rewrite is the only byte-level trust boundary.

## Notes

- All values marked "changes with game updates" should be regenerated when analyzing new binary versions
- The YAML file is written to the same directory as the input binary
- vtable_size is automatically calculated as `vtable_numvfunc * pointer_size`
- vtable_rva is automatically calculated as `vtable_va - image_base`