source: vbox/trunk/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SelProtFar16DataToRealMode.asm

; $Id: bs3-cmn-SelProtFar16DataToRealMode.asm 106061 2024-09-16 14:03:52Z vboxsync $
;; @file
; BS3Kit - Bs3SelProtFar16DataToRealMode.
;

;
; Copyright (C) 2007-2024 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
;


;*********************************************************************************************************************************
;*      Header Files                                                                                                             *
;*********************************************************************************************************************************
%include "bs3kit-template-header.mac"


;*********************************************************************************************************************************
;*  External Symbols                                                                                                             *
;*********************************************************************************************************************************
BS3_BEGIN_DATA16                        ; For real mode segment value.
BS3_BEGIN_SYSTEM16                      ; Ditto.
TMPL_BEGIN_TEXT
BS3_EXTERN_CMN Bs3SelFar32ToFlat32NoClobber

TMPL_BEGIN_TEXT
%if TMPL_BITS == 16
CPU 8086
%endif


;;
; @cproto   BS3_CMN_PROTO_NOSB(uint32_t, Bs3SelProtFar16DataToRealMode,(uint32_t uFar1616));
;
; @uses     Only return registers (ax:dx, eax, eax)
; @remarks  No 20h scratch area requirements.
;
BS3_PROC_BEGIN_CMN Bs3SelProtFar16DataToRealMode, BS3_PBC_NEAR      ; Far stub generated by the makefile/bs3kit.h.
        push    xBP
        mov     xBP, xSP

        ;
        ; See if it's our default 16-bit ring-0 data, stack or system data segment.
        ;
%if TMPL_BITS == 16
        mov     ax, [xBP + xCB + cbCurRetAddr + 2]
%elif TMPL_BITS == 32
        movzx   eax, word [xBP + xCB + cbCurRetAddr + 2]
%else
        mov     eax, ecx
        shr     eax, 16
%endif
        cmp     ax, BS3_SEL_R0_SS16
        jne     .not_stack
        mov     ax, 0

.quick_return:
%if TMPL_BITS == 16
        mov     dx, ax
        mov     ax, [xBP + xCB + cbCurRetAddr]
%elif TMPL_BITS == 32
        shl     eax, 16
        mov     ax, word [xBP + xCB + cbCurRetAddr]
%else
        shl     eax, 16
        mov     ax, cx
%endif

.return:
        pop     xBP
        BS3_HYBRID_RET

.not_stack:
        cmp     ax, BS3_SEL_R0_DS16
        jne     .not_dgroup
        mov     ax, BS3KIT_GRPNM_DATA16
        jmp     .quick_return

.not_dgroup:
        cmp     ax, BS3_SEL_SYSTEM16
        jne     .not_system16
        mov     ax, BS3SYSTEM16
        jmp     .quick_return

        ;
        ; Call worker function to convert it to flat and the do tiled
        ; calculation from that.
        ;
.not_system16:
%if TMPL_BITS == 16
        push    word [xBP + xCB + cbCurRetAddr + 2]
        xor     ax, ax
        push    ax
        push    word [xBP + xCB + cbCurRetAddr]
        call    Bs3SelFar32ToFlat32NoClobber
        add     sp, 6

        ; Convert upper 16-bit of the flat address to a tiled selector.
        push    cx
        mov     cl, X86_SEL_SHIFT
        shl     dx, cl
        add     dx, BS3_SEL_TILED
        pop     cx
%else
 %if TMPL_BITS == 32
        push    eax
        movzx   eax, word [xBP + xCB + cbCurRetAddr]
        push    eax
        call    Bs3SelFar32ToFlat32NoClobber
        add     esp, 8
 %else
        push    xDX
        push    xCX

        mov     edx, eax                ; arg #2: selector
        movzx   ecx, cx                 ; arg #1: offset
        call    Bs3SelFar32ToFlat32NoClobber

        pop     xDX
        pop     xCX
 %endif

        ; Convert upper 16-bit to tiled selector.
        rol     eax, 16
        shl     ax, X86_SEL_SHIFT
        add     ax, BS3_SEL_TILED
        ror     eax, 16
%endif
        jmp     .return
BS3_PROC_END_CMN   Bs3SelProtFar16DataToRealMode