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-rw-r--r--arch/x86/boot/bootsect.s32
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"