chkstk_stub

A minimal Rust build helper crate that provides a stub implementation of the macOS/iOS runtime function __chkstk_darwin.

Why this crate exists

When building C/C++ code for iOS or macOS using Rust, you may encounter linker errors like:

Undefined symbols for architecture arm64:
  "___chkstk_darwin", referenced from:
      ...

This happens when your code (or a dependency) uses large stack allocations, and the platform would normally insert a call to __chkstk_darwin — but the symbol is missing in your build environment. On some targets, especially when cross-compiling static libraries, the function isn’t automatically provided.

chkstk_stub solves this by compiling and linking a no-op version of the function:

void __chkstk_darwin(void) {}

This is safe if:

You control all code that might hit this call site.

You are certain that large stack allocations are safe in your environment.

You just need to bypass the missing symbol to get a successful build.

How it works

The build.rs file in this crate:

1. Writes chkstk_stub.c into the Cargo build output directory (OUT_DIR).

2. Compiles it into a static library using the cc crate.

3. Ensures Cargo links the resulting libchkstk_stub.a into your build.

Usage

[build-dependencies]
chkstk_stub = { version = "0.1.0" }

Notes & Warnings

• This is not a full implementation of __chkstk_darwin — it’s a no-op.

• In most cases, stack probing is only needed for large stack frames; skipping it may be safe for your use case, but you should verify.

• This is intended for linker unblocking in controlled build environments, not as a general-purpose solution for production code.