Tracking Issue for RFC 3543 patchable-function-entry

This is a tracking issue for the RFC 3543 patchable-function-entry (rust-lang/rfcs#3543).

The feature gate for the issue is #![feature(patchable_function_entry)].

This is support for patchable-function-entry as present in clang and gcc. This feature is generally used to allow hotpatching and instrumentation of code.

About tracking issues

Tracking issues are used to record the overall progress of implementation. They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions. A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature. Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Implement the RFC: https://github.com/rust-lang/rust/pull/124741
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• Should we use LLVM or gcc/clang style for a per-function attribute? Should we support both styles?
• Should we support a more explicit command line argument style?
• Should we reject linking crates with different default padding configurations?