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; $Id: bs3-cmn-SwitchTo16BitV86.asm $
;; @file
; BS3Kit - Bs3SwitchTo16BitV86
;
;
; Copyright (C) 2007-2023 Oracle and/or its affiliates.
;
; This file is part of VirtualBox base platform packages, as
; available from https://www.virtualbox.org.
;
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License
; as published by the Free Software Foundation, in version 3 of the
; License.
;
; This program is distributed in the hope that it will be useful, but
; WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
; General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program; if not, see <https://www.gnu.org/licenses>.
;
; The contents of this file may alternatively be used under the terms
; of the Common Development and Distribution License Version 1.0
; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
; in the VirtualBox distribution, in which case the provisions of the
; CDDL are applicable instead of those of the GPL.
;
; You may elect to license modified versions of this file under the
; terms and conditions of either the GPL or the CDDL or both.
;
; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
;
%include "bs3kit-template-header.mac"
%if TMPL_BITS != 64
BS3_EXTERN_DATA16 g_bBs3CurrentMode
BS3_EXTERN_CMN Bs3SwitchToRing0
BS3_EXTERN_CMN Bs3SelProtFar32ToFlat32
TMPL_BEGIN_TEXT
;;
; @cproto BS3_DECL(void) Bs3SwitchTo16BitV86(void);
; @uses No general registers modified. Regment registers loaded with specific
; values and the stack register converted to real mode (not ebp).
;
BS3_PROC_BEGIN_CMN Bs3SwitchTo16BitV86, BS3_PBC_NEAR
; Construct basic v8086 return frame.
BONLY16 movzx esp, sp
push dword 0 ; +0x20: GS
push dword 0 ; +0x1c: FS
push dword BS3_SEL_DATA16 ; +0x18: ES
push dword BS3_SEL_DATA16 ; +0x14: DS
push dword 0 ; +0x10: SS - later
push dword 0 ; +0x0c: return ESP, later.
pushfd
or dword [esp], X86_EFL_VM | X86_EFL_IOPL ; +0x08: Set IOPL=3 and the VM flag (EFLAGS).
push dword BS3_SEL_TEXT16 ; +0x04
push word 0
push word [esp + 24h - 2] ; +0x00
; Save registers and stuff.
push eax
push edx
push ecx
push ebx
%if TMPL_BITS == 16
push ds
; Check g_bBs3CurrentMode whether we're in v8086 mode or not.
mov ax, seg g_bBs3CurrentMode
mov ds, ax
mov al, [BS3_DATA16_WRT(g_bBs3CurrentMode)]
test al, BS3_MODE_CODE_V86
jz .not_v8086
pop ds
pop ebx
pop ecx
pop edx
pop eax
add xSP, 0x24
ret
.not_v8086:
pop ax ; Drop the push ds so the stacks are identical. Keep DS = BS3KIT_GRPNM_DATA16 though.
%endif
; Ensure that we're in ring-0.
mov ax, ss
test ax, 3
jz .is_ring0
call Bs3SwitchToRing0
%if TMPL_BITS == 16
mov ax, seg g_bBs3CurrentMode
mov ds, ax ; parnoia
%endif
.is_ring0:
; Update globals.
and byte [BS3_DATA16_WRT(g_bBs3CurrentMode)], ~BS3_MODE_CODE_MASK
or byte [BS3_DATA16_WRT(g_bBs3CurrentMode)], BS3_MODE_CODE_V86
; Thunk return SS:ESP to real-mode address via 32-bit flat.
lea eax, [esp + 4*4 + 24h + xCB]
push ss
push eax
BS3_CALL Bs3SelProtFar32ToFlat32, 2
add esp, sCB + xCB
mov [esp + 4*4 + 0ch], ax ; high word is already zero
%if TMPL_BITS == 16
mov [esp + 4*4 + 10h], dx
%else
shr eax, 16
mov [esp + 4*4 + 10h], ax
%endif
; Return to v8086 mode.
pop ebx
pop ecx
pop edx
pop eax
iretd
BS3_PROC_END_CMN Bs3SwitchTo16BitV86
;; @todo far 16-bit variant.
%endif ; ! 64-bit
|
