diff options
| -rw-r--r-- | src/cpu/x86/16bit/entry16.inc | 15 |
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) |