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Diffstat (limited to 'src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToLM16.asm')
| -rw-r--r-- | src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToLM16.asm | 126 |
1 files changed, 126 insertions, 0 deletions
diff --git a/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToLM16.asm b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToLM16.asm new file mode 100644 index 00000000..51da27ce --- /dev/null +++ b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToLM16.asm @@ -0,0 +1,126 @@ +; $Id: bs3-mode-SwitchToLM16.asm $ +;; @file +; BS3Kit - Bs3SwitchToLM16 +; + +; +; Copyright (C) 2007-2019 Oracle Corporation +; +; This file is part of VirtualBox Open Source Edition (OSE), as +; available from http://www.virtualbox.org. This file is free software; +; you can redistribute it and/or modify it under the terms of the GNU +; General Public License (GPL) as published by the Free Software +; Foundation, in version 2 as it comes in the "COPYING" file of the +; VirtualBox OSE distribution. VirtualBox OSE is distributed in the +; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind. +; +; The contents of this file may alternatively be used under the terms +; of the Common Development and Distribution License Version 1.0 +; (CDDL) only, as it comes in the "COPYING.CDDL" file of the +; VirtualBox OSE 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. +; + +%include "bs3kit-template-header.mac" + + +;; +; Switch to 16-bit long mode from any other mode. +; +; @cproto BS3_DECL(void) Bs3SwitchToLM16(void); +; +; @uses Nothing (except possibly high 32-bit and/or upper 64-bit register parts). +; +; @remarks Obviously returns to 16-bit mode, even if the caller was in 32-bit +; or 64-bit mode. It doesn't not preserve the callers ring, but +; instead changes to ring-0. +; +; @remarks Does not require 20h of parameter scratch space in 64-bit mode. +; +%if TMPL_BITS == 16 +BS3_GLOBAL_NAME_EX TMPL_NM(Bs3SwitchToLM16_Safe), function , 0 +%endif +BS3_PROC_BEGIN_MODE Bs3SwitchToLM16, BS3_PBC_NEAR +%ifdef TMPL_LM16 + extern BS3_CMN_NM(Bs3SwitchToRing0) + call BS3_CMN_NM(Bs3SwitchToRing0) + push ax + mov ax, BS3_SEL_R0_DS16 + mov ds, ax + mov es, ax + pop ax + ret + +%elifdef TMPL_CMN_LM + ; + ; Already in long mode, just switch to 16-bit. + ; + extern BS3_CMN_NM(Bs3SwitchTo16Bit) + jmp BS3_CMN_NM(Bs3SwitchTo16Bit) + +%else + ; + ; Switch to LM32 and then switch to 64-bits (IDT & TSS are the same for + ; LM16, LM32 and LM64, unlike the rest). + ; + ; (The long mode switching code is going via 32-bit protected mode, so + ; Bs3SwitchToLM32 contains the actual code for switching to avoid + ; unnecessary 32-bit -> 64-bit -> 32-bit trips.) + ; + extern TMPL_NM(Bs3SwitchToLM32) + call TMPL_NM(Bs3SwitchToLM32) + BS3_SET_BITS 32 + + extern _Bs3SwitchTo16Bit_c32 + %if TMPL_BITS == 16 + sub esp, 2 + shr dword [esp], 16 + %elif TMPL_BITS == 64 + pop dword [esp + 4] + %endif + jmp _Bs3SwitchTo16Bit_c32 +%endif +BS3_PROC_END_MODE Bs3SwitchToLM16 + + +%if TMPL_BITS == 16 +;; +; Custom far stub. +BS3_BEGIN_TEXT16_FARSTUBS +BS3_PROC_BEGIN_MODE Bs3SwitchToLM16, BS3_PBC_FAR + inc bp + push bp + mov bp, sp + + ; Call the real thing. + call TMPL_NM(Bs3SwitchToLM16) + + %if BS3_MODE_IS_RM_OR_V86(TMPL_MODE) + ; Jmp to common code for the tedious conversion. + BS3_EXTERN_CMN Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn + jmp Bs3SwitchHlpConvRealModeRetfPopBpDecBpAndReturn + %else + pop bp + dec bp + retf + %endif +BS3_PROC_END_MODE Bs3SwitchToLM16 + +%else +;; +; Safe far return to non-BS3TEXT16 code. +BS3_EXTERN_CMN Bs3SwitchHlpConvFlatRetToRetfProtMode +BS3_BEGIN_TEXT16 +BS3_SET_BITS TMPL_BITS +BS3_PROC_BEGIN_MODE Bs3SwitchToLM16_Safe, BS3_PBC_NEAR + call Bs3SwitchHlpConvFlatRetToRetfProtMode ; Special internal function. Uses nothing, but modifies the stack. + call TMPL_NM(Bs3SwitchToLM16) + BS3_SET_BITS 16 + retf +BS3_PROC_END_MODE Bs3SwitchToLM16_Safe + +%endif + |