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-rw-r--r--src/cpu/x86/16bit/entry16.inc15
1 files changed, 8 insertions, 7 deletions
diff --git a/src/cpu/x86/16bit/entry16.inc b/src/cpu/x86/16bit/entry16.inc
index 0fa8c11524..e4613bf986 100644
--- a/src/cpu/x86/16bit/entry16.inc
+++ b/src/cpu/x86/16bit/entry16.inc
@@ -57,13 +57,6 @@ _start:
* entry16.inc.
*/
- /* Load an IDT with NULL limit to prevent the 16bit IDT being used
- * in protected mode before c_start.S sets up a 32bit IDT when entering
- * ram stage.
- */
- movw $nullidt_offset, %bx
- lidt %cs:(%bx)
-
/* Note: gas handles memory addresses in 16 bit code very poorly.
* In particular it doesn't appear to have a directive allowing you
* associate a section or even an absolute offset with a segment register.
@@ -98,10 +91,18 @@ _start:
* the low 16 bits. This means that the intial segment used
* when start is called must be 64K aligned. This should not
* restrict the address as the ip address can be anything.
+ *
+ * Also load an IDT with NULL limit to prevent the 16bit IDT being used
+ * in protected mode before c_start.S sets up a 32bit IDT when entering
+ * ram stage. In practise: CPU will shutdown on any exception.
+ * See IA32 manual Vol 3A 19.26 Interrupts.
*/
movw %cs, %ax
shlw $4, %ax
+ movw $nullidt_offset, %bx
+ subw %ax, %bx
+ lidt %cs:(%bx)
movw $gdtptr16_offset, %bx
subw %ax, %bx
data32 lgdt %cs:(%bx)