#pair #expressions #getter #generate #function #refer #calls

getfn

A utility crate for generating function pairs to refer to functions via custom expressions

6 releases

0.2.0 Nov 3, 2023
0.1.4 Nov 3, 2023
0.1.1 Jun 1, 2021
0.1.0 Feb 22, 2021

#1777 in Rust patterns

MIT/Apache

15KB
301 lines

Crates.io

getfn

Utilities for referring to functions by pointer.

Using the getfn! macro, you can generate a pair of functions: the first function acts as a "getter" function, and is prefixed with getfn_. The second function simply calls the function normally:

use getfn::getfn;

getfn! {
	(|| { println!("hi!"); })
	fn my_func();
}

my_func(); // hi!
let f = getfn_my_func();
f(); // hi!

You might be wondering why not simply use let f = my_func; instead of having a separate getter. The reason is that the resulting function pointer in f will not have the exact same address as the one passed into getfn!. This is necessary in cases like game modding, where to hook a function, you must have its exact address. To aid these usecases, getfn also offers a get_addr! macro, which is a DSL for getting the address of a function:

// gets the base address of the `MyGame.exe` module using the backend
// specified via features (currently supported are `winapi` and `libc`).
let f = getfn::get_addr!("MyGame.exe" + 0x20bf00);

These can be combined together using the symbol_fn! macro:

use getfn::symbol_fn;
use std::ffi::c_void;

symbol_fn! {
	("MyGame.exe" + 0x20bf00)
	extern "C" fn my_game_func(a: i32) -> bool;
}
println!("{}", my_game_func(5));

let func = getfn_my_game_func();

extern "C" fn detour(a: i32) -> bool { a == 5 }

// .. hook `func` ..
let mut orig = std::ptr::null_mut();
MH_CreateHook(func as *mut c_void, detour, &mut orig as *mut _ as _);

License

Licensed under either of

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Dependencies