FFI and Extern

Scope

This document defines the language-level contract for external bindings. Runtime ownership and syscall policy are specified in docs/execution/runtime/syscalls-and-abi-boundary.md.

18.1 Extern declaration model

Extern bindings are expressed using the Extern attribute.

[Extern(Abi: "C", Library: "libc")]
pub mod LibC {
    pub i64 write(i32 fd, ref u8 buf, i64 count);
}

18.2 Required attribute arguments

• Abi MUST be a compile-time string literal.
• Library MUST be a compile-time string literal.
• Unsupported or malformed values MUST produce source-located diagnostics.

18.3 Type and signature constraints

• Extern function signatures MUST use representable ABI-compatible types.
• Unsupported high-level-only types in extern signatures MUST be rejected.
• Extern declarations define interface contracts; they do not imply runtime ownership policy.

18.4 Language/runtime boundary

• Language spec owns syntax, typing, and diagnostics for extern declarations.
• Execution spec owns symbol resolution/loading/linking behavior and syscall mediation.

18.5 Non-goals

• This document does not define per-platform syscall behavior.
• This document does not define runtime dispatch implementation details.