Make "iretq" instruction return to rust function

[proxin187]

Hi!

I am currently in the process of implementing a round robin scheduler for my kernel in rust, i found a nice and simple example of scheduling at EliaOnceAgain/edu-x86-bootloader-kernel and i started implementing my scheduler in a similar fashion as the example, it all went smooth until i had to return to my "next_process" function with the iretq instruction.

asm!(
    // we want to make iretq return to the next_process function.
    "push next_process",
    "iretq",
);

#[no_mangle]
pub extern "C" fn next_process() {
    // here we are restoring the register state but it doesnt matter for this post.
}

When i try to compile this i get the following linker error:

  = note: rust-lld: error: relocation R_X86_64_32S cannot be used against symbol 'next_process'; recompile with -fPIC
          >>> defined in /home/proxin/Rust/lios/kernel/target/x86_64-unknown-none/debug/deps/lios-c028c9a0db928179.58u4cutpp6ltkxvokpvh3beeg.rcgu.o
          >>> referenced by mod.rs:73 (src/interrupt/mod.rs:73)
          >>>               /home/proxin/Rust/lios/kernel/target/x86_64-unknown-none/debug/deps/lios-c028c9a0db928179.4uvqmwk2pnqtk3sygjmer33y5.rcgu.o:(lios::interrupt::timer_interrupt::hc490168c73fff0b9)

To sum up i am looking for a way to make the iretq instruction call next_process when returning from a interrupt.

If anyone knows how to achieve this i would greatly appreciate some help!

[bjorn3]

Try push [rip + next_process] for pc-relative addressing. Rust generates PIC executables by default, which requires using pc-relative rather than absolute addressing.