This example project demonstrates the dynamic linkage behavior of override static variable in some situation:

How to run

cargo run

Output (In Ubuntu 16.04)

Calling some_staticlib::get_global_direct()
[some_staticlib/src/lib.rs:5] p_global_var = 0x00007f977c43695c
Calling some_dy::get_global_var_from_dy)
[some_staticlib/src/lib.rs:11] p_global_var = 0x00007f977b1c16c0
Calling some_dy::cget_global_var_direct)
[some_staticlib/src/lib.rs:5] p_global_var = 0x00007f977c43695c

The "meat" of the code

dy_panic/src/main.rs

Lines 22 to 55 in 98e399a

	fn main() -> Result<(), std::io::Error> {
	println!("Calling some_staticlib::get_global_direct()");
	some_staticlib::get_global_direct();
	let dy_path = find_some_dy()?;
	let lib = DynamicLibrary::open(Some(&dy_path)).expect("Cannot open dynamic library!");
	let call_from_dy = unsafe {
	match lib.symbol("get_global_var_from_dy") {
	Err(e) => {
	panic!("{:#?}", e);
	}
	Ok(f) => std::mem::transmute::<*mut u8, fn() -> u32>(f),
	}
	};
	let call_from_direct = unsafe {
	match lib.symbol("get_global_var_direct") {
	Err(e) => {
	panic!("{:#?}", e);
	}
	Ok(f) => std::mem::transmute::<*mut u8, fn() -> u32>(f),
	}
	};
	println!("Calling some_dy::get_global_var_from_dy)");
	call_from_dy();
	println!("Calling some_dy::cget_global_var_direct)");
	call_from_direct();
	Ok(())
	}

dy_panic/some_dy/src/lib.rs

Lines 1 to 9 in 98e399a

	#[no_mangle]
	pub extern "C" fn get_global_var_from_dy() -> u32 {
	some_staticlib::get_global_from_dy()
	}
	#[no_mangle]
	pub extern "C" fn get_global_var_direct() -> u32 {
	some_staticlib::get_global_direct()
	}

https://github.com/edwin0cheng/dy_panic/blob/98e399a70d26eb754cc09d320090d098ac25980c/some_staticlib/src/lib.rs#L1-L15

Explanation

In src/main.rs:

• call some_staticlib::get_global_direct() (static linkage)
• call some_dy::get_global_var_from_dy (dynamic linkgage)
  • in some_dy , call some_staticlib::get_global_var_from_dy() (static linkage with some_dy)
• call some_dy::get_global_var_direct (dynamic linkgage)
  • in some_dy , call some_staticlib::get_global_var_direct() (static linkage with some_dy)

Note that although some_dy::get_global_var_from_dy and some_dy::get_global_var_direct are wrapped in dynamic library, the dynamic linker is smart enough to know that the underneath some_staticlib::get_global_var_direct() can be shared.