load_itcm: use zst

src/hardware/setup.rs

@@ -152,9 +152,10 @@ static mut DES_RING: MaybeUninit<
 /// this method is undefined.
 fn load_itcm() {
     extern "C" {
-        static mut __sitcm: u32;
-        static mut __eitcm: u32;
-        static mut __siitcm: u32;
+        // ZST (`()`: not layout-stable. empty/zst struct in `repr(C)``: not "proper" C)
+        static mut __sitcm: [u32; 0];
+        static mut __eitcm: [u32; 0];
+        static mut __siitcm: [u32; 0];
     }
     // NOTE(unsafe): Assuming the address symbols from the linker as well as
     // the source instruction data are all valid, this is safe as it only
@@ -170,9 +171,9 @@ fn load_itcm() {
         // Ensure ITCM is enabled before loading.
         atomic::fence(Ordering::SeqCst);
 
-        let sitcm = core::ptr::addr_of_mut!(__sitcm);
-        let eitcm = core::ptr::addr_of_mut!(__eitcm);
-        let siitcm = core::ptr::addr_of_mut!(__siitcm);
+        let sitcm = core::ptr::addr_of_mut!(__sitcm) as *mut u32;
+        let eitcm = core::ptr::addr_of!(__eitcm) as *const u32;
+        let siitcm = core::ptr::addr_of!(__siitcm) as *const u32;
 
         let len = eitcm.offset_from(sitcm) as usize;
         let dst = slice::from_raw_parts_mut(sitcm, len);