Patched everything for aarch64, aside from scheduler, add more linker

points to aarch64 ld, add aarch64 heap, init, page tables and usermode,
make hhdm_offset a global atomic, aarch64 uses semihosting for output,
add generic PageTable type, add a function that creates and maps pages,
use allow to remove warnings, add a bufwriter so kernel panic always
works

kernel/src/task/context.rs

@@ -1,5 +1,6 @@
 use crate::task::scheduler::{SCHEDULER, current_pid};
 
+#[cfg(target_arch = "x86_64")]
 #[repr(C)]
 #[derive(Clone, Copy)]
 pub struct UserContext {
@@ -22,6 +23,11 @@ pub struct UserContext {
     pub rsp: u64, // user rsp
 }
 
+#[cfg(target_arch = "aarch64")]
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub struct UserContext {}
+
 #[unsafe(no_mangle)]
 pub extern "C" fn ctx_save(regs: *const UserContext) {
     if let Some(pid) = current_pid() {