diff options
Diffstat (limited to 'src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16Bit.asm')
| -rw-r--r-- | src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16Bit.asm | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16Bit.asm b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16Bit.asm new file mode 100644 index 00000000..1e1d8747 --- /dev/null +++ b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16Bit.asm @@ -0,0 +1,130 @@ +; $Id: bs3-cmn-SwitchTo16Bit.asm $ +;; @file +; BS3Kit - Bs3SwitchTo16Bit +; + +; +; 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" + +BS3_EXTERN_DATA16 g_bBs3CurrentMode +%if TMPL_BITS == 16 +BS3_EXTERN_CMN Bs3Syscall +%endif +TMPL_BEGIN_TEXT + + +;; +; @cproto BS3_DECL(void) Bs3SwitchTo16Bit(void); +; @remarks Does not require 20h of parameter scratch space in 64-bit mode. +; +BS3_PROC_BEGIN_CMN Bs3SwitchTo16Bit, BS3_PBC_NEAR +%if TMPL_BITS == 16 + push ax + push ds + + ; Check g_bBs3CurrentMode whether we're in v8086 mode or not. + mov al, [BS3_DATA16_WRT(g_bBs3CurrentMode)] + test al, BS3_MODE_CODE_V86 + jz .ret_16bit + + ; Switch to ring-0 if v8086 mode. + mov ax, BS3_SYSCALL_TO_RING0 + call Bs3Syscall + +.ret_16bit: + pop ds + pop ax + ret + +%else + push xAX + push xBX + xPUSHF + cli + + ; Calc new CS. + mov ax, cs + and xAX, 3 + shl xAX, BS3_SEL_RING_SHIFT ; ring addend. + add xAX, BS3_SEL_R0_CS16 + + ; Construct a far return for switching to 16-bit code. + push xAX + push .sixteen_bit + xRETF + +BS3_BEGIN_TEXT16 +BS3_GLOBAL_LOCAL_LABEL .sixteen_bit + + ; Load 16-bit segment registers. + add ax, BS3_SEL_R0_SS16 - BS3_SEL_R0_CS16 + mov ss, ax + + add ax, BS3_SEL_R0_DS16 - BS3_SEL_R0_SS16 + mov ds, ax + mov es, ax + + ; Thunk the stack if necessary. + mov ebx, esp + shr ebx, 16 + jz .stack_ok +int3 ; This is for later, just remove this int3 once needed. + test ax, X86_SEL_RPL + jnz .stack_rpl_must_be_0_for_custom_stacks + shl bx, X86_SEL_SHIFT + add bx, BS3_SEL_TILED + mov ss, bx + movzx esp, sp +.stack_ok: + + ; Update globals. + and byte [BS3_DATA16_WRT(g_bBs3CurrentMode)], ~BS3_MODE_CODE_MASK + or byte [BS3_DATA16_WRT(g_bBs3CurrentMode)], BS3_MODE_CODE_16 + + popfd +TONLY64 pop ebx + pop ebx +TONLY64 pop eax + pop eax +TONLY64 add sp, 4 + ret (TMPL_BITS - 16) / 8 ; Return and pop 2 or 6 bytes of "parameters" (unused return value) + +.stack_rpl_must_be_0_for_custom_stacks: + int3 + jmp .stack_rpl_must_be_0_for_custom_stacks +TMPL_BEGIN_TEXT +%endif +BS3_PROC_END_CMN Bs3SwitchTo16Bit + +;; @todo far 16-bit variant. + |