fixup! Allow the guest to manage its own stack

Add more comments on new architecture-specific code

Signed-off-by: Lucy Menon <168595099+syntactically@users.noreply.github.com>

Author: syntactically

src/hyperlight_guest_bin/src/arch/amd64/init.rs

@@ -104,6 +104,8 @@ unsafe fn init_tss(pc: *mut ProcCtrl) {
     }
 }
 
+/// To initialise the main stack, we just pre-emptively map the first
+/// page of it.
 unsafe fn init_stack() -> u64 {
     use hyperlight_guest::layout::MAIN_STACK_TOP_GVA;
     let stack_top_page_base = (MAIN_STACK_TOP_GVA - 1) & !0xfff;
@@ -122,11 +124,18 @@ unsafe fn init_stack() -> u64 {
 #[unsafe(no_mangle)]
 pub extern "C" fn entrypoint(peb_address: u64, seed: u64, ops: u64, max_log_level: u64) {
     unsafe {
+        // Allocate a VA for processor control structures which must
+        // survive snapshotting at the same VA.
         let pc = ProcCtrl::init();
+
         init_gdt(pc);
         init_tss(pc);
         init_idt(pc);
         let stack_top = init_stack();
+
+        // Architecture early init is complete! We pivot now to
+        // executing on the main stack, and jump into generic
+        // initialisation code in lib.rs
         pivot_stack(peb_address, seed, ops, max_log_level, stack_top);
     }
 }