Thunk16.asm revision 4fd606d1f5abe38e1f42c38de1d2e895166bd0f4
#include "BaseLibInternals.h"
;------------------------------------------------------------------------------
;
; Copyright (c) 2006 - 2011, Intel Corporation. All rights reserved.<BR>
; This program and the accompanying materials
; are licensed and made available under the terms and conditions of the BSD License
; which accompanies this distribution. The full text of the license may be found at
;
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
;
; Module Name:
;
;
; Abstract:
;
; Real mode thunk
;
;------------------------------------------------------------------------------
.686p
.model flat,C
EXTERNDEF C m16Start:BYTE
EXTERNDEF C m16Size:WORD
EXTERNDEF C mThunk16Attr:WORD
EXTERNDEF C m16Gdt:WORD
EXTERNDEF C m16GdtrBase:WORD
EXTERNDEF C mTransition:WORD
;
; Here is the layout of the real mode stack. _ToUserCode() is responsible for
; loading all these registers from real mode stack.
;
IA32_REGS STRUC 4t
_EDI DD ?
_ESI DD ?
_EBP DD ?
_ESP DD ?
_EBX DD ?
_EDX DD ?
_ECX DD ?
_EAX DD ?
_DS DW ?
_ES DW ?
_FS DW ?
_GS DW ?
_EFLAGS DD ?
_EIP DD ?
_CS DW ?
_SS DW ?
IA32_REGS ENDS
.const
;
; These are global constant to convey information to C code.
;
m16Size DW InternalAsmThunk16 - m16Start
mThunk16Attr DW _ThunkAttr - m16Start
m16Gdt DW _NullSegDesc - m16Start
m16GdtrBase DW _16GdtrBase - m16Start
mTransition DW _EntryPoint - m16Start
.code
m16Start LABEL BYTE
SavedGdt LABEL FWORD
DW ?
DD ?
;------------------------------------------------------------------------------
; _BackFromUserCode() takes control in real mode after 'retf' has been executed
; by user code. It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_BackFromUserCode PROC
;
; The order of saved registers on the stack matches the order they appears
; in IA32_REGS structure. This facilitates wrapper function to extract them
; into that structure.
;
push ss
push cs
DB 66h
call @Base ; push eip
@Base:
pushf ; pushfd actually
cli ; disable interrupts
push gs
push fs
push es
push ds
pushaw ; pushad actually
DB 66h, 0bah ; mov edx, imm32
_ThunkAttr DD ?
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
jz @1
mov eax, 15cd2401h ; mov ax, 2401h & int 15h
cli ; disable interrupts
jnc @2
@1:
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
jz @2
in al, 92h
or al, 2
out 92h, al ; deactivate A20M#
@2:
xor ax, ax ; xor eax, eax
mov eax, ss ; mov ax, ss
DB 67h
lea bp, [esp + sizeof (IA32_REGS)]
;
; esi's in the following 2 instructions are indeed bp in 16-bit code. Fact
; is "esi" in 32-bit addressing mode has the same encoding of "bp" in 16-
; bit addressing mode.
;
mov word ptr (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._ESP, bp
mov ebx, (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._EIP
shl ax, 4 ; shl eax, 4
add bp, ax ; add ebp, eax
DB 66h, 0b8h ; mov eax, imm32
SavedCr4 DD ?
mov cr4, eax
DB 66h
lgdt fword ptr cs:[edi + (SavedGdt - @Base)]
DB 66h, 0b8h ; mov eax, imm32
SavedCr0 DD ?
mov cr0, eax
DB 0b8h ; mov ax, imm16
SavedSs DW ?
mov ss, eax
DB 66h, 0bch ; mov esp, imm32
SavedEsp DD ?
DB 66h
retf ; return to protected mode
_BackFromUserCode ENDP
_EntryPoint DD _ToUserCode - m16Start
DW 8h
_16Idtr FWORD (1 SHL 10) - 1
_16Gdtr LABEL FWORD
DW GdtEnd - _NullSegDesc - 1
_16GdtrBase DD _NullSegDesc
;------------------------------------------------------------------------------
; _ToUserCode() takes control in real mode before passing control to user code.
; It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_ToUserCode PROC
mov edx, ss
mov ss, ecx ; set new segment selectors
mov ds, ecx
mov es, ecx
mov fs, ecx
mov gs, ecx
mov cr0, eax
mov cr4, ebp ; real mode starts at next instruction
mov ss, esi ; set up 16-bit stack segment
xchg sp, bx ; set up 16-bit stack pointer
DB 66h
call @Base ; push eip
@Base:
pop bp ; ebp <- address of @Base
DB 67h ; address size override
push [esp + sizeof (IA32_REGS) + 2]
lea eax, [esi + (@RealMode - @Base)]
push eax
retf
@RealMode:
mov cs:[esi + (SavedSs - @Base)], edx
mov cs:[esi + (SavedEsp - @Base)], bx
DB 66h
lidt fword ptr cs:[esi + (_16Idtr - @Base)]
popaw ; popad actually
pop ds
pop es
pop fs
pop gs
popf ; popfd
DB 66h ; Use 32-bit addressing for "retf" below
retf ; transfer control to user code
_ToUserCode ENDP
_NullSegDesc DQ 0
_16CsDesc LABEL QWORD
DW -1
DW 0
DB 0
DB 9bh
DB 8fh ; 16-bit segment, 4GB limit
DB 0
_16DsDesc LABEL QWORD
DW -1
DW 0
DB 0
DB 93h
DB 8fh ; 16-bit segment, 4GB limit
DB 0
GdtEnd LABEL QWORD
;------------------------------------------------------------------------------
; IA32_REGISTER_SET *
; EFIAPI
; InternalAsmThunk16 (
; IN IA32_REGISTER_SET *RegisterSet,
; IN OUT VOID *Transition
; );
;------------------------------------------------------------------------------
InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs
mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter
movzx edx, (IA32_REGS ptr [esi])._SS
mov edi, (IA32_REGS ptr [esi])._ESP
add edi, - (sizeof (IA32_REGS) + 4) ; reserve stack space
mov ebx, edi ; ebx <- stack offset
imul eax, edx, 16 ; eax <- edx * 16
push sizeof (IA32_REGS) / 4
add edi, eax ; edi <- linear address of 16-bit stack
pop ecx
rep movsd ; copy RegSet
mov eax, [esp + 40] ; eax <- address of transition code
mov esi, edx ; esi <- 16-bit stack segment
lea edx, [eax + (SavedCr0 - m16Start)]
mov ecx, eax
and ecx, 0fh
shl eax, 12
lea ecx, [ecx + (_BackFromUserCode - m16Start)]
mov ax, cx
stosd ; [edi] <- return address of user code
sgdt fword ptr [edx + (SavedGdt - SavedCr0)]
sidt fword ptr [esp + 36] ; save IDT stack in argument space
mov eax, cr0
mov [edx], eax ; save CR0 in SavedCr0
and eax, 7ffffffeh ; clear PE, PG bits
mov ebp, cr4
mov [edx + (SavedCr4 - SavedCr0)], ebp
and ebp, 300h ; clear all but PCE and OSFXSR bits
push 10h
pop ecx ; ecx <- selector for data segments
lgdt fword ptr [edx + (_16Gdtr - SavedCr0)]
pushfd ; Save df/if indeed
call fword ptr [edx + (_EntryPoint - SavedCr0)]
popfd
lidt fword ptr [esp + 36] ; restore protected mode IDTR
lea eax, [ebp - sizeof (IA32_REGS)] ; eax <- the address of IA32_REGS
ret
InternalAsmThunk16 ENDP
END