alduin 0.0.1

WIP: A toy compiler backend
Documentation 
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use crate::{
    backend::ISA,
    compiler::compiled_code::{CallSite, Symbol},
};

use super::X64;

/// A static dispatch call site
pub(super) struct X64StaticCallSite {
    symbol: Symbol,
    offset: usize,
    start: *const u8,
}

unsafe impl Send for X64StaticCallSite {}
unsafe impl Sync for X64StaticCallSite {}

impl X64StaticCallSite {
    pub fn new(symbol: Symbol, offset: usize) -> Self {
        Self {
            symbol,
            offset,
            start: 0 as _,
        }
    }

    pub fn set_start_address(&mut self, start: *const u8) {
        self.start = start;
    }
}

impl CallSite for X64StaticCallSite {
    fn symbol(&self) -> &Symbol {
        &self.symbol
    }

    fn patch(&self, addr: *const u8) {
        unsafe {
            let return_address = self.start.add(self.offset);
            let slot = self.start.add(self.offset - 4) as *mut i32;
            let rel_offset: i32 = addr.offset_from(return_address) as i32;
            std::ptr::write_unaligned(slot, rel_offset);
            X64::flush_cache(slot as *const u8, 4)
        }
    }
}