Ffi design

FFI Design Skill

Overview

Expert skill for designing and implementing foreign function interfaces to native code.

Capabilities

• Design FFI declaration syntax
• Implement type marshaling between languages
• Handle C calling conventions (cdecl, stdcall, fastcall)
• Implement callback support (native calling managed)
• Handle string encoding conversions
• Implement struct layout matching (padding, alignment)
• Design memory ownership transfer rules
• Support dynamic library loading

Target Processes

• ffi-implementation.js
• interpreter-implementation.js
• bytecode-vm-implementation.js
• code-generation-llvm.js

Dependencies

• libffi
• Platform ABI documentation

Usage Guidelines

1. Safety: Design safe wrappers around unsafe FFI calls
2. Marshaling: Document type marshaling rules explicitly
3. Ownership: Make memory ownership clear at FFI boundaries
4. Callbacks: Handle callback lifetimes carefully
5. Strings: Handle string encoding conversions correctly (UTF-8, UTF-16)

Output Schema

{
  "type": "object",
  "properties": {
    "callingConventions": {
      "type": "array",
      "items": { "type": "string" }
    },
    "marshalingRules": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "sourceType": { "type": "string" },
          "targetType": { "type": "string" }
        }
      }
    },
    "callbackSupport": { "type": "boolean" },
    "generatedFiles": {
      "type": "array",
      "items": { "type": "string" }
    }
  }
}