Merge pull request #328 from Stary2001/fix-stage2

Correctness fixes for stage2

Author: phil-opp

bios/stage-2/src/main.rs

@@ -39,10 +39,11 @@ pub extern "C" fn _start(disk_number: u16, partition_table_start: *const u8) ->
 }
 
 fn start(disk_number: u16, partition_table_start: *const u8) -> ! {
-    screen::Writer.write_str(" -> SECOND STAGE\n").unwrap();
-
+    // Enter unreal mode before doing anything else.
     enter_unreal_mode();
 
+    screen::Writer.write_str(" -> SECOND STAGE\n").unwrap();
+
     // parse partition table
     let partitions = {
         const MAX_ENTRIES: usize = 4;

bios/stage-2/src/protected_mode.rs

@@ -59,8 +59,10 @@ unsafe impl Sync for GdtPointer {}
 
 pub fn enter_unreal_mode() {
     let ds: u16;
+    let ss: u16;
     unsafe {
         asm!("mov {0:x}, ds", out(reg) ds, options(nomem, nostack, preserves_flags));
+        asm!("mov {0:x}, ss", out(reg) ss, options(nomem, nostack, preserves_flags));
     }
 
     GDT.clear_interrupts_and_load();
@@ -70,14 +72,15 @@ pub fn enter_unreal_mode() {
 
     // load GDT
     unsafe {
-        asm!("mov {0}, 0x10", "mov ds, {0}", out(reg) _);
+        asm!("mov {0}, 0x10", "mov ds, {0}", "mov ss, {0}", out(reg) _);
     }
 
     // unset protected mode bit again
     write_cr0(cr0);
 
     unsafe {
         asm!("mov ds, {0:x}", in(reg) ds, options(nostack, preserves_flags));
+        asm!("mov ss, {0:x}", in(reg) ss, options(nostack, preserves_flags));
         asm!("sti");
     }
 }