hello.c

#include <stdio.h>

void print_hello(void) {
    printf("hello\n");
}

hello.h

void print_hello(void);

Makefile

CC = gcc
RUSTC = rustc
BINDGEN = bindgen

test: test.rs hello.rs libhello.so
	$(RUSTC) $< -L . -o $@

hello.rs: hello.h
	$(BINDGEN) -l hello $< -o $@

libhello.so: hello.c
	$(CC) -fPIC -shared $< -o $@

clean:
	$(RM) -f test hello.rs libhello.so

.PHONY: clean

test.rs

mod hello;

#[fixed_stack_segment]
fn main() {
    unsafe {
        hello::print_hello();
    }
}