diff options
Diffstat (limited to 'src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16BitV86.asm')
| -rw-r--r-- | src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16BitV86.asm | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16BitV86.asm b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16BitV86.asm new file mode 100644 index 00000000..636e6184 --- /dev/null +++ b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16BitV86.asm @@ -0,0 +1,133 @@ +; $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 + |