diff options
Diffstat (limited to 'arch/x86/lib/realmode_switch.S')
| -rw-r--r-- | arch/x86/lib/realmode_switch.S | 61 |
1 files changed, 36 insertions, 25 deletions
diff --git a/arch/x86/lib/realmode_switch.S b/arch/x86/lib/realmode_switch.S index 7ee709a..c4c4c43 100644 --- a/arch/x86/lib/realmode_switch.S +++ b/arch/x86/lib/realmode_switch.S @@ -44,12 +44,13 @@ * e40 ss; */ -#define a32 .byte 0x67; /* address size prefix 32 */ -#define o32 .byte 0x66; /* operand size prefix 32 */ +#define a32 .byte 0x67; /* address size prefix 32 */ +#define o32 .byte 0x66; /* operand size prefix 32 */ .section .realmode, "ax" .code16 - /* 16bit protected mode code here */ + + /* 16bit protected mode code here */ .globl realmode_enter realmode_enter: o32 pusha @@ -69,20 +70,23 @@ o32 pushf movw %ax, %gs lidt realmode_idt_ptr - movl %cr0, %eax /* Go back into real mode by */ - andl $0x7ffffffe, %eax /* clearing PE to 0 */ + /* Go back into real mode by clearing PE to 0 */ + movl %cr0, %eax + andl $0x7ffffffe, %eax movl %eax, %cr0 - ljmp $0x0,$do_realmode /* switch to real mode */ -do_realmode: /* realmode code from here */ + /* switch to real mode */ + ljmp $0x0,$do_realmode + +do_realmode: + /* realmode code from here */ movw %cs,%ax movw %ax,%ds movw %ax,%es movw %ax,%fs movw %ax,%gs - /* create a temporary stack */ - + /* create a temporary stack */ movw $0xc0, %ax movw %ax, %ss movw $0x200, %ax @@ -114,26 +118,29 @@ o32 popf popw %ss movl %eax, %esp cs movl temp_eax, %eax - wbinvd /* self-modifying code, - * better flush the cache */ + + /* self-modifying code, better flush the cache */ + wbinvd .byte 0x9a /* lcall */ temp_ip: .word 0 /* new ip */ temp_cs: .word 0 /* new cs */ + realmode_ret: - /* save eax, esp and ss */ + /* save eax, esp and ss */ cs movl %eax, saved_eax movl %esp, %eax cs movl %eax, saved_esp movw %ss, %ax cs movw %ax, saved_ss - /* restore the stack, note that we set sp to 0x244; + /* + * restore the stack, note that we set sp to 0x244; * pt_regs is 0x44 bytes long and we push the structure - * backwards on to the stack, bottom first */ - + * backwards on to the stack, bottom first + */ movw $0xc0, %ax movw %ax, %ss movw $0x244, %ax @@ -169,12 +176,15 @@ cs movw temp_ip, %ax pushl %ebx o32 cs lidt saved_idt -o32 cs lgdt saved_gdt /* Set GDTR */ +o32 cs lgdt saved_gdt - movl %cr0, %eax /* Go back into protected mode */ - orl $1,%eax /* reset PE to 1 */ + /* Go back into protected mode reset PE to 1 */ + movl %cr0, %eax + orl $1,%eax movl %eax, %cr0 - jmp next_line /* flush prefetch queue */ + + /* flush prefetch queue */ + jmp next_line next_line: movw $return_ptr, %ax movw %ax,%bp @@ -182,12 +192,13 @@ o32 cs ljmp *(%bp) .code32 protected_mode: - movl $0x18,%eax /* reload GDT[3] */ - movw %ax,%fs /* reset FS */ - movw %ax,%ds /* reset DS */ - movw %ax,%gs /* reset GS */ - movw %ax,%es /* reset ES */ - movw %ax,%ss /* reset SS */ + /* Reload segment registers */ + movl $0x18, %eax + movw %ax, %fs + movw %ax, %ds + movw %ax, %gs + movw %ax, %es + movw %ax, %ss movl saved_protected_mode_esp, %eax movl %eax, %esp popf |