Field Context

func_sig

Overview

func_sig is the primary function relocation signature used in {symbol}.{platform}.yaml.

Field Context

• Related YAML fields: func_name, func_va, func_rva, func_size, func_sig.
• Typical role: relocate the target function in a new binary version via unique byte-pattern match.

Generation Principle

• Canonical auto-generation is implemented by preprocess_gen_func_sig_via_mcp in ida_analyze_util.py.
• Input is a known function start address (func_va).
• Bytes are collected from the function head instruction-by-instruction.
• Volatile bytes are wildcarded (??), including immediates/displacements and relative branch/call offsets.
• Candidate signatures grow only at instruction boundaries.
• Every candidate is checked by find_bytes(limit=2) for uniqueness.
• A candidate is accepted only if it uniquely matches and the match address equals the target function head.
• The shortest accepted candidate is emitted as func_sig.

Usage Method

• In version-to-version preprocessing (preprocess_func_sig_via_mcp), func_sig is the primary relocation anchor.
• Flow:
  1. Run find_bytes with old func_sig.
  2. Require exactly one match.
  3. Query IDA function info at match address (func_va, func_size).
  4. Recompute func_rva and write new YAML.
• Important behavior: if old YAML already has func_sig, preprocessing chooses this path first and does not auto-fallback to vfunc_sig on failure.

Downstream Use

• Dist gamedata modules mainly consume func_sig (converted to target pattern formats like CSS/VDF/Swiftly variants).

Practical Notes

• Keep uniqueness strict (==1 match); multi-hit signatures are invalid.
• Ensure signature anchors function head, not an interior address.
• Overly short signatures may pass today but become unstable in future updates.