Crate relative

A type to wrap vtable references such that they can be safely sent between other processes running the same binary.

Crates.io │ Repo

References are adjusted relative to a base when (de)serialised, which is what enables it to work across binaries that are dynamically loaded at different addresses under multiple invocations.

It being the same binary is checked by serialising the build_id alongside the relative pointer, which is validated at deserialisation.

Example

Local process

use std::{fmt::Display, mem::transmute, raw::TraitObject};

let mut x: Box<dyn Display> = Box::new("hello world");
let x_ptr: *mut dyn Display = &mut *x;
let x_ptr: TraitObject = unsafe { transmute(x_ptr) };
let relative = unsafe { Vtable::<dyn Display>::from(&*x_ptr.vtable) };
// send `relative` to remote...

Remote process

// receive `relative`
let x: Box<&str> = Box::new("goodbye world");
let x_ptr = Box::into_raw(x);
let y_ptr = TraitObject { data: x_ptr.cast(), vtable: relative.to() as *const () as *mut () };
let y_ptr: *mut dyn Display = unsafe { transmute(y_ptr) };
let y: Box<dyn Display> = unsafe { Box::from_raw(y_ptr) };
println!("{}", y);
// prints "goodbye world"

Structs

• Vtable
  Wraps &'static references to vtables such that they can be safely sent between other processes running the same binary.