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|
; $Id: bs3-mode-SwitchToPE16.asm $
;; @file
; BS3Kit - Bs3SwitchToPE16
;
;
; 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 unpaged protected mode from any other mode.
;
; @cproto BS3_DECL(void) Bs3SwitchToPE16(void);
;
; @uses Nothing (except high 32-bit register parts).
;
; @remarks Obviously returns to 16-bit mode, even if the caller was
; in 32-bit or 64-bit mode.
;
; @remarks Does not require 20h of parameter scratch space in 64-bit mode.
;
%if TMPL_BITS == 16
BS3_GLOBAL_NAME_EX TMPL_NM(Bs3SwitchToPE16_Safe), function , 0
%endif
BS3_PROC_BEGIN_MODE Bs3SwitchToPE16, BS3_PBC_NEAR
%ifdef TMPL_PE16
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
%elif BS3_MODE_IS_V86(TMPL_MODE)
;
; V8086 - Switch to 16-bit ring-0 and call worker for that mode.
;
extern BS3_CMN_NM(Bs3SwitchToRing0)
call BS3_CMN_NM(Bs3SwitchToRing0)
extern %[BS3_MODE_R0_NM_ %+ TMPL_MODE](Bs3SwitchToPE16)
jmp %[BS3_MODE_R0_NM_ %+ TMPL_MODE](Bs3SwitchToPE16)
%else
;
; Switch to 16-bit mode and prepare for returning in 16-bit mode.
;
%if TMPL_BITS != 16
shl xPRE [xSP], TMPL_BITS - 16 ; Adjust the return address.
add xSP, xCB - 2
; Must be in 16-bit segment when calling Bs3SwitchTo16Bit.
jmp .sixteen_bit_segment
BS3_BEGIN_TEXT16
BS3_SET_BITS TMPL_BITS
BS3_GLOBAL_LOCAL_LABEL .sixteen_bit_segment
%endif
;
; Switch to real mode.
;
extern TMPL_NM(Bs3SwitchToRM)
call TMPL_NM(Bs3SwitchToRM)
BS3_SET_BITS 16
push ax
push cx
pushf
cli
;
; Load the GDT and enable PE16.
;
BS3_EXTERN_SYSTEM16 Bs3Lgdt_Gdt
BS3_EXTERN_SYSTEM16 Bs3LgdtDef_Gdt
BS3_BEGIN_TEXT16
mov ax, BS3SYSTEM16
mov ds, ax
lgdt [Bs3LgdtDef_Gdt] ; Will only load 24-bit base!
smsw ax
or ax, X86_CR0_PE
lmsw ax
;
; Convert from real mode stack to protected mode stack.
;
mov ax, .p16_stack
extern NAME(Bs3ConvertRMStackToP16UsingCxReturnToAx_c16)
jmp NAME(Bs3ConvertRMStackToP16UsingCxReturnToAx_c16)
.p16_stack:
;
; Call routine for doing mode specific setups.
;
extern NAME(Bs3EnteredMode_pe16)
call NAME(Bs3EnteredMode_pe16)
;
; Load full 32-bit GDT base address from 32-bit segment, if 386+ CPU.
;
BS3_EXTERN_DATA16 g_uBs3CpuDetected
BS3_BEGIN_TEXT16
cmp byte [g_uBs3CpuDetected], BS3CPU_80386
jb .old_cpu_skip_32bit_lgdt
push ds
mov ax, BS3_SEL_SYSTEM16
mov ds, ax
jmp dword BS3_SEL_R0_CS32:.load_full_gdt_base wrt FLAT
.load_full_gdt_base:
BS3_SET_BITS 32
lgdt [Bs3Lgdt_Gdt wrt BS3SYSTEM16]
jmp BS3_SEL_R0_CS16:.back_to_16bit
.back_to_16bit:
BS3_SET_BITS 16
pop ds
.old_cpu_skip_32bit_lgdt:
popf
pop cx
pop ax
ret
%if TMPL_BITS != 16
TMPL_BEGIN_TEXT
%endif
%endif
BS3_PROC_END_MODE Bs3SwitchToPE16
%if TMPL_BITS == 16
;;
; Custom far stub.
BS3_BEGIN_TEXT16_FARSTUBS
BS3_PROC_BEGIN_MODE Bs3SwitchToPE16, BS3_PBC_FAR
inc bp
push bp
mov bp, sp
; Call the real thing.
call TMPL_NM(Bs3SwitchToPE16)
%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 Bs3SwitchToPE16
%else
;;
; Safe far return to non-BS3TEXT16 code.
BS3_EXTERN_CMN Bs3SwitchHlpConvFlatRetToRetfProtMode
BS3_BEGIN_TEXT16
BS3_SET_BITS TMPL_BITS
BS3_PROC_BEGIN_MODE Bs3SwitchToPE16_Safe, BS3_PBC_NEAR
call Bs3SwitchHlpConvFlatRetToRetfProtMode ; Special internal function. Uses nothing, but modifies the stack.
call TMPL_NM(Bs3SwitchToPE16)
BS3_SET_BITS 16
retf
BS3_PROC_END_MODE Bs3SwitchToPE16_Safe
%endif
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