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; $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
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