stage1: return sorted memory map

stage1/src/mem.rs

@@ -1,6 +1,7 @@
 use crate::asm::{do_bios_int, BiosIntRegs};
 use core::cmp::Ordering;
 use core::mem::size_of;
+use core::ptr::slice_from_raw_parts_mut;
 
 #[derive(Eq, PartialEq)]
 #[repr(C)]
@@ -14,26 +15,28 @@ pub struct MemMapEntry {
 const SMAP: u32 = 0x534d4150;
 
 /// Use int15/e820 to detect the entire installed system memory.
+/// The entries are sorted by ascending start address.
 ///
 /// ## Safety
 ///
 /// `dest` must be aligned to at least 8 bytes, accessible from real mode,
 /// and have enough capacity to store the entire memory map.  In practice,
 /// we use a 64 K segment, which should be way more than sufficient.
-pub unsafe fn read_bios_mmap(mut dest: *mut MemMapEntry) -> usize {
+pub unsafe fn read_bios_mmap(dest: *mut MemMapEntry) -> usize {
     let mut offset: u32 = 0;
     let mut count: usize = 0;
     debug_assert!((dest as *mut MemMapEntry as usize) < 0x10_0000);
+    let mut pos = dest;
 
     loop {
-        dest.as_mut().unwrap_unchecked().acpi30_ext = 1;
+        pos.as_mut().unwrap_unchecked().acpi30_ext = 1;
         let regs = BiosIntRegs {
             eax: 0xe820,
             ecx: size_of::<MemMapEntry>() as u32,
             edx: SMAP,
             ebx: offset,
-            edi: ((dest as usize) % 0x10) as u32,
-            es: ((dest as usize) / 0x10) as u16,
+            edi: ((pos as usize) % 0x10) as u32,
+            es: ((pos as usize) / 0x10) as u16,
             ..Default::default()
         };
         let result = match do_bios_int(0x15, regs) {
@@ -42,13 +45,13 @@ pub unsafe fn read_bios_mmap(mut dest: *mut MemMapEntry) -> usize {
         };
 
         if result.ecx < size_of::<MemMapEntry>() as u32 {
-            dest.as_mut().unwrap_unchecked().acpi30_ext = 1;
+            pos.as_mut().unwrap_unchecked().acpi30_ext = 1;
         }
         if result.eax != SMAP {
             break;
         }
         count += 1;
-        dest = dest.add(1);
+        pos = pos.add(1);
         if result.ebx == 0 {
             break;
         } else {
@@ -56,6 +59,11 @@ pub unsafe fn read_bios_mmap(mut dest: *mut MemMapEntry) -> usize {
         }
     }
 
+    let mmap_mut = slice_from_raw_parts_mut(dest, count)
+        .as_mut()
+        .unwrap_unchecked();
+    mmap_mut.sort_unstable();
+
     count
 }