diff options
| -rw-r--r-- | arch/x86/boot/bootsect.s | 32 |
1 files changed, 31 insertions, 1 deletions
diff --git a/arch/x86/boot/bootsect.s b/arch/x86/boot/bootsect.s index eedf3bd..e2ab91c 100644 --- a/arch/x86/boot/bootsect.s +++ b/arch/x86/boot/bootsect.s @@ -46,12 +46,39 @@ load_kernel: # Load our kernel cmp %al, %al # If AL(sect. read) != <>(sect. expected) jne disk_error # then return disk error - jmp . # TODO: jump into the darkness +switch_to_pm: + BIOS_PRINT $boot_prot_mode_msg + cli # Switch of interrupt until we have set + # up the protected mode interrupt vector + lgdt gdt_descriptor # Load our global descriptor table + + mov %cr0, %eax # Set the first bit of CR0 + or $0x01, %eax # to make the switch to protected mode + mov %eax, %cr0 + + # Make a far jump to our 32-bit code. + # This also forces the CPU to flush its cache of pre-fetched + # and real-mode decoded instructions, which can cause problems + jmp $CODESEG, $init_pm disk_error: BIOS_PRINT $disk_error_msg jmp . +.code32 +init_pm: + mov $DATASEG, %ax # Point segment registers to the + mov %ax, %ds # data selector we defined in our GDT + mov %ax, %es + mov %ax, %ss + mov %ax, %fs + mov %ax, %gs + + mov $0x90000, %ebp # Update stack position so it is right + mov %ebp, %esp # at the top of the free space. + + jmp . # infinite loop + # Global Descriptor Table (contains 8-byte entries) gdt_start: gdt_null: # The mandatory null descriptor @@ -90,6 +117,9 @@ gdt_descriptor: boot_real_mode_msg: .asciz "Started mfsos in 16-bit real mode\r\n" +boot_prot_mode_msg: + .asciz "Entering 32-bit protected mode\r\n" + boot_load_kern_msg: .asciz "Loading kernel into memory\r\n" |