Learn unsafe Rust: Provide initial content for the chapter "ABI and FFI"

[darkwisebear]

Todo

Provide initial content for the ABI and FFI chapter of the Learn unsafe Rust book.

Proposed content

• Explain ABI and what "C ABI/FFI" actually means
  • What aspects of the ABI are defined by C and which aren't
  • How compilers and compiler settings influence the ABI
  • What aspects are influenced by the ABI
  • Mismatching calling conventions / padding (aka ABI)
  • Note on different calling conventions, esp. on x86
• Explain unsafety categories in FFI
  • Explain main building blocks of the Rust FFI
  • Mismatching function signatures
  • Mismatching type declarations
  • Unsafe actions beyond the FFI boundary
  • Moveability/self-reference, especially with C++ move constructors
  • Ownership
  • C++ topics
    • Dealing with standard library data structures
    • Exceptions thrown from C++ code
• Mitigations for FFI unsafety
  • Existing FFI tooling (bindgen, cbindgen, cxx)
  • Checks that can be done on FFI and Rust side
  • cRABI (?)

[darkwisebear]

I started writing stuff and uploaded that to my personal repo fork: https://github.com/darkwisebear/learn_unsafe_rust/blob/initial_content_abi_ffi/src/core_unsafety/abi_and_ffi.md. Feel free to create PRs to that or comment here on what's there already.

[PLeVasseur]

Hey @darkwisebear, thanks for kicking this off for ABI and FFI :)

I'd like to keep our merges back to the repo consistent. Consider opening a PR based on your branch to here to raise awareness. I'm very happy to merge even partially completed sections as @iglesias has been doing.

[darkwisebear]

I can open a draft PR; I don't want to merge it as-is, it's really half-baked still, but people can anyway already start commenting if they want to.

[PLeVasseur]

Hey sorry I probably was not clear! I meant to open a PR to this repo, not the Learn unsafe Rust, with any intermediate work. That way we can have a chance to collaborate and merge pieces. I agree that for contributing back to Learn unsafe Rust we'd want one comprehensive package of work.

[darkwisebear]

@PLeVasseur Understood, yeah, I can do that. I will just put the file into a subdir of this repo, keeping the structure of the original repo.

[PLeVasseur]

@PLeVasseur Understood, yeah, I can do that. I will just put the file into a subdir of this repo, keeping the structure of the original repo.

Great, sounds like a good plan! Thanks for starting it.