Is there an easier way of calling functions at static addresses?

Question

I am using Rust to write a DLL that is going to be injected into other process and I want to call functions that are located at known addresses from the executable of that process. I use transmute to cast a hardcoded address to a function pointer but I might potentially have many functions and I'd like an easier way of managing that.

Ideally I'd only have extern "C" declarations like when linking with a DLL instead of an implementation with copy-pasted cast for each function.

lib.rs

fn add_one(i: u32) -> u32 {
    let add_one_from_exe_location = 0xd51000;
    let add_one_from_exe: unsafe extern "C" fn(u32) -> u32 =
        unsafe { std::mem::transmute(add_one_from_exe_location as *const ()) };
    unsafe { add_one_from_exe(i) }
}

fn hello() {
    println!("hello from dll");
    println!("1 + 1 = {}", add_one(1));
}

#[no_mangle]
pub extern "stdcall" fn DllMain(
    _: winapi::shared::minwindef::HINSTANCE,
    fdw_reason: winapi::shared::minwindef::DWORD,
    _lpv_reserved: winapi::shared::minwindef::LPVOID,
) -> i32 {
    match fdw_reason {
        winapi::um::winnt::DLL_PROCESS_ATTACH => {
            hello();
        }
        _ => (),
    }
    true as i32
}

Here's an example of an executable

main.rs

#[no_mangle]
extern "C" fn add_one(x: u32) -> u32 {
    x + 1
}
fn main() {
    use std::{thread, time};
    let mut x = 0;
    loop {
        x = add_one(x);
        thread::sleep(time::Duration::from_millis(1000));
        println!("{}", x);
    }
}

When I inject the DLL it outputs

41
hello from dll
1 + 1 = 2
42

`usize -> *const () -> fn pointer` is the only way, as stated in the duplicate. Perhaps you can write a macro to reduce the boilerplate. — Shepmaster, Jan 05 '21 at 18:10
I demonstrate that I am already doing exactly what the "duplicate" suggests, I want an easier way to manage that — vpoverennov, Jan 05 '21 at 18:11
Yes, and if there _were_ an easier way, that answer would belong on the duplicate, which I've now enhanced with an example of a macro. Otherwise, there'd be an infinite chain of questions "is there an easier way of doing X than previous_question_1"... "is there an easier way of doing X than previous_question_2" ... etc. — Shepmaster, Jan 05 '21 at 18:17
And if you find an old question that you want to draw attention to (maybe things _have_ changed since it was answered) then the appropriate Stack Overflow method is to place a bounty on the question. — Shepmaster, Jan 05 '21 at 18:22

Is there an easier way of calling functions at static addresses?

0 Answers0