1 files changed, 118 insertions, 0 deletions
diff --git a/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToPEV86.asm b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToPEV86.asm
new file mode 100644
index 00000000..3796d91e
--- /dev/null
+++ b/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-mode-SwitchToPEV86.asm
@@ -0,0 +1,118 @@
+; $Id: bs3-mode-SwitchToPEV86.asm $
+;; @file
+; BS3Kit - Bs3SwitchToPEV86
+;
+
+;
+; Copyright (C) 2007-2022 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"
+
+
+;;
+; Switch to 16-bit v8086 unpaged protected mode with 32-bit sys+tss from any other mode.
+;
+; @cproto   BS3_DECL(void) Bs3SwitchToPEV86(void);
+;
+; @uses     Nothing (except high 32-bit register parts).
+;
+; @remarks  Obviously returns to 16-bit v8086 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(Bs3SwitchToPEV86_Safe), function , 0
+%endif
+BS3_PROC_BEGIN_MODE Bs3SwitchToPEV86, BS3_PBC_NEAR
+%if TMPL_MODE == BS3_MODE_PEV86
+        ret
+
+%else
+        ;
+        ; Switch to 32-bit PE32 and from there to V8086.
+        ;
+        extern  TMPL_NM(Bs3SwitchToPE32)
+        call    TMPL_NM(Bs3SwitchToPE32)
+        BS3_SET_BITS 32
+
+        ;
+        ; Switch to v8086 mode after adjusting the return address.
+        ;
+ %if TMPL_BITS == 16
+        push    word [esp]
+        mov     word [esp + 2], 0
+ %elif TMPL_BITS == 64
+        pop     dword [esp + 4]
+ %endif
+        extern  _Bs3SwitchTo16BitV86_c32
+        jmp     _Bs3SwitchTo16BitV86_c32
+%endif
+BS3_PROC_END_MODE   Bs3SwitchToPEV86
+
+
+%if TMPL_BITS == 16
+;;
+; Custom far stub.
+BS3_BEGIN_TEXT16_FARSTUBS
+BS3_PROC_BEGIN_MODE Bs3SwitchToPEV86, BS3_PBC_FAR
+        inc         bp
+        push        bp
+        mov         bp, sp
+
+        ; Call the real thing.
+        call        TMPL_NM(Bs3SwitchToPEV86)
+
+ %if !BS3_MODE_IS_RM_OR_V86(TMPL_MODE)
+        ; Jmp to common code for the tedious conversion.
+        BS3_EXTERN_CMN Bs3SwitchHlpConvProtModeRetfPopBpDecBpAndReturn
+        jmp         Bs3SwitchHlpConvProtModeRetfPopBpDecBpAndReturn
+ %else
+        pop         bp
+        dec         bp
+        retf
+ %endif
+BS3_PROC_END_MODE   Bs3SwitchToPEV86
+
+%else
+;;
+; Safe far return to non-BS3TEXT16 code.
+BS3_EXTERN_CMN Bs3SwitchHlpConvFlatRetToRetfProtMode
+BS3_BEGIN_TEXT16
+BS3_SET_BITS TMPL_BITS
+BS3_PROC_BEGIN_MODE Bs3SwitchToPEV86_Safe, BS3_PBC_NEAR
+        call        Bs3SwitchHlpConvFlatRetToRetfProtMode ; Special internal function.  Uses nothing, but modifies the stack.
+        call        TMPL_NM(Bs3SwitchToPEV86)
+        BS3_SET_BITS 16
+        retf
+BS3_PROC_END_MODE   Bs3SwitchToPEV86_Safe
+%endif
+