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|
; $Id: bs3-cmn-SelFlatCodeToRealMode.asm $
;; @file
; BS3Kit - Bs3SelFlatCodeToRealMode.
;
;
; Copyright (C) 2007-2023 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"
;*********************************************************************************************************************************
;* Global Variables *
;*********************************************************************************************************************************
BS3_EXTERN_DATA16 Bs3RmText16_EndOfSegment
BS3_EXTERN_DATA16 Bs3X0Text16_EndOfSegment
BS3_EXTERN_DATA16 Bs3X1Text16_EndOfSegment
;
; Make sure we can get at all the segments.
;
BS3_BEGIN_TEXT16
BS3_BEGIN_RMTEXT16
BS3_BEGIN_X0TEXT16
BS3_BEGIN_X1TEXT16
TMPL_BEGIN_TEXT
;;
; @cproto BS3_CMN_PROTO(uint32_t, Bs3SelRealModeCodeToProtMode,(uint32_t uFlatAddr), false);
;
; @uses Only return registers (ax:dx, eax, eax)
;
BS3_PROC_BEGIN_CMN Bs3SelFlatCodeToRealMode, BS3_PBC_NEAR
BS3_CALL_CONV_PROLOG 1
push xBP
mov xBP, xSP
push xCX
push xBX
%if TMPL_BITS != 16
push xDX
%endif
;
; Load the real mode frame number into DX so we can compare with the
; segment frame numbers fixed up by the linker.
;
; Imagine: FlatAddr = 0x054321
;
mov dx, [xBP + xCB + cbCurRetAddr + 1] ; dx = 0x0543
mov al, [xBP + xCB + cbCurRetAddr + 0] ; al = 0x21
mov cl,4
shl dx, 4 ; dx = 0x5430
shr al, 4 ; al = 0x02
or dl, al ; dx = 0x5432
mov ax, dx
sub ax, CGROUP16
cmp ax, 1000h
jb .bs3text16
mov ax, dx
sub ax, BS3GROUPRMTEXT16
mov bx, Bs3RmText16_EndOfSegment wrt BS3GROUPRMTEXT16
add bx, 15
shr bx, cl
cmp ax, bx
jb .bs3rmtext16
mov ax, dx
sub ax, BS3GROUPX0TEXT16
mov bx, Bs3X0Text16_EndOfSegment wrt BS3GROUPX0TEXT16
add bx, 15
shr bx, cl
cmp ax, bx
jb .bs3x0text16
mov ax, dx
sub ax, BS3GROUPX1TEXT16
mov bx, Bs3X1Text16_EndOfSegment wrt BS3GROUPX1TEXT16
add bx, 15
shr bx, cl
cmp ax, bx
jb .bs3x1text16
extern BS3_CMN_NM(Bs3Panic)
call BS3_CMN_NM(Bs3Panic)
;
; Load the real-mode frame into DX and calc the offset in AX.
;
.bs3x1text16:
mov dx, BS3GROUPX1TEXT16
jmp .calc_return
.bs3x0text16:
mov dx, BS3GROUPX0TEXT16
jmp .calc_return
.bs3rmtext16:
mov dx, BS3GROUPRMTEXT16
jmp .calc_return
.bs3text16:
mov dx, CGROUP16
.calc_return:
; Convert the real-mode frame into the low 16-bit base (BX).
mov bx, dx
shl bx, cl
; Subtract the 16-bit base from the flat address. (No need to consider
; the top half on either side.)
mov ax, [xBP + xCB + cbCurRetAddr + 0]
sub ax, bx
%if TMPL_BITS != 16
; Got a single 32-bit return register here.
shl edx, 16
mov dx, ax
mov eax, edx
pop xDX
%endif
pop xBX
pop xCX
pop xBP
BS3_CALL_CONV_EPILOG 1
BS3_HYBRID_RET
BS3_PROC_END_CMN Bs3SelFlatCodeToRealMode
;
; We may be using the near code in some critical code paths, so don't
; penalize it.
;
BS3_CMN_FAR_STUB Bs3SelFlatCodeToRealMode, 4
|
