expand on safety requirements

Author: Restioson

src/structures/gdt.rs

@@ -450,7 +450,8 @@ impl Descriptor {
     /// # Safety
     ///
     /// There must be a valid IO map at `(tss as *const u8).offset(tss.iomap_base)`
-    /// of length `iomap_size`
+    /// of length `iomap_size`, with the terminating `0xFF` byte. Additionally, `iomap_base` must
+    /// not exceed `0xDFFF`.
     pub unsafe fn tss_segment_with_iomap(
         tss: &'static TaskStateSegment,
         iomap_size: u16,

src/structures/tss.rs

@@ -19,7 +19,8 @@ pub struct TaskStateSegment {
     pub interrupt_stack_table: [VirtAddr; 7],
     reserved_3: u64,
     reserved_4: u16,
-    /// The 16-bit offset to the I/O permission bit map from the 64-bit TSS base.
+    /// The 16-bit offset to the I/O permission bit map from the 64-bit TSS base. It must not
+    /// exceed `0xDFFF`.
     pub iomap_base: u16,
 }