diff options
| -rw-r--r-- | boot/arch/amd64/mbr/mbr.S | 29 |
1 files changed, 24 insertions, 5 deletions
diff --git a/boot/arch/amd64/mbr/mbr.S b/boot/arch/amd64/mbr/mbr.S index 236f9f1..4c8c993 100644 --- a/boot/arch/amd64/mbr/mbr.S +++ b/boot/arch/amd64/mbr/mbr.S @@ -1,19 +1,38 @@ /* Segment constants */ -#define BOOT_SEG 0x7C0 /* Segment we reside on startup */ +#define BOOT_SEG 0x7C0 /* Segment we reside on startup */ +#define BOOT_RELOC_SEG 0x7A0 /* Relocation segment */ .code16 _start: /* Normalize CS + other selectors */ ljmp $BOOT_SEG,$1f 1: xor %ax, %ax - mov %ax, %ds mov %ax, %ss - mov %ax, %es mov %ax, %gs mov %ax, %fs -2: cli + + /* + * The second stage bootloader expects to be loaded to 0x7C00 but since we are + * already executing at this address we'll need to relocate ourselves first before + * we clobber it. + */ + mov $BOOT_SEG, %ax + mov %ax, %ds + mov $BOOT_RELOC_SEG, %ax + mov %ax, %es + xor %si, %si + xor %di, %di + mov $0x200, %cx + cld + rep movsb + + /* Jump to our relocated self */ + ljmp $BOOT_RELOC_SEG,$reloc + +reloc: + cli hlt - jmp 2b + jmp reloc .org 510 .byte 0x55 |