; $Id: bs3-mode-SwitchToPE16.asm 69111 2017-10-17 14:26:02Z vboxsync $ ;; @file ; BS3Kit - Bs3SwitchToPE16 ; ; ; Copyright (C) 2007-2017 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