| 1 | ; $Id: bs3-cmn-ConvertRMStackToP16UsingCxReturnToAx.asm 98103 2023-01-17 14:15:46Z vboxsync $
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| 2 | ;; @file
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| 3 | ; BS3Kit - Bs3ConvertRMStackToP16UsingCxReturnToAx.
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| 4 | ;
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| 5 |
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| 6 | ;
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| 7 | ; Copyright (C) 2007-2023 Oracle and/or its affiliates.
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| 8 | ;
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| 9 | ; This file is part of VirtualBox base platform packages, as
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| 10 | ; available from https://www.virtualbox.org.
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| 11 | ;
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| 12 | ; This program is free software; you can redistribute it and/or
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| 13 | ; modify it under the terms of the GNU General Public License
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| 14 | ; as published by the Free Software Foundation, in version 3 of the
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| 15 | ; License.
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| 16 | ;
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| 17 | ; This program is distributed in the hope that it will be useful, but
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| 18 | ; WITHOUT ANY WARRANTY; without even the implied warranty of
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| 19 | ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 20 | ; General Public License for more details.
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| 21 | ;
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| 22 | ; You should have received a copy of the GNU General Public License
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| 23 | ; along with this program; if not, see <https://www.gnu.org/licenses>.
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| 24 | ;
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| 25 | ; The contents of this file may alternatively be used under the terms
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| 26 | ; of the Common Development and Distribution License Version 1.0
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| 27 | ; (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
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| 28 | ; in the VirtualBox distribution, in which case the provisions of the
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| 29 | ; CDDL are applicable instead of those of the GPL.
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| 30 | ;
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| 31 | ; You may elect to license modified versions of this file under the
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| 32 | ; terms and conditions of either the GPL or the CDDL or both.
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| 33 | ;
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| 34 | ; SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
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| 35 | ;
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| 36 |
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| 37 | %include "bs3kit-template-header.mac"
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| 38 |
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| 39 |
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| 40 | %if TMPL_BITS != 16
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| 41 | %error 16-bit only!
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| 42 | %endif
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| 43 |
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| 44 | ;;
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| 45 | ; An internal helper for converting a real-mode stack into a 16-bit protected
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| 46 | ; mode stack.
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| 47 | ;
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| 48 | ; This is used by the mode switchers that ends up in 16-bit mode. It is
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| 49 | ; assumed that we're in ring-0.
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| 50 | ;
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| 51 | ; @param ax The return address.
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| 52 | ;
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| 53 | ; @uses cx, ss, esp
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| 54 | ;
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| 55 | BS3_PROC_BEGIN_CMN Bs3ConvertRMStackToP16UsingCxReturnToAx, BS3_PBC_NEAR
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| 56 |
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| 57 | ;
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| 58 | ; Check if it looks like the normal stack, if use BS3_SEL_R0_SS16.
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| 59 | ;
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| 60 | mov cx, ss
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| 61 | cmp cx, 0
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| 62 | jne .stack_tiled
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| 63 | mov cx, BS3_SEL_R0_SS16
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| 64 | mov ss, cx
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| 65 | jmp ax
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| 66 |
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| 67 | ;
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| 68 | ; Some custom stack address, just use the 16-bit tiled mappings
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| 69 | ;
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| 70 | .stack_tiled:
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| 71 | int3 ; debug this, shouldn't happen yet. Bs3EnteredMode_xxx isn't prepared.
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| 72 | shl cx, 4
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| 73 | add sp, cx
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| 74 | mov cx, ss
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| 75 | jc .stack_carry
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| 76 | shr cx, 12
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| 77 | jmp .stack_join_up_again
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| 78 | .stack_carry:
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| 79 | shr cx, 12
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| 80 | inc cx
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| 81 | .stack_join_up_again:
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| 82 | shl cx, 3
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| 83 | adc cx, BS3_SEL_TILED
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| 84 | mov ss, cx
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| 85 | jmp ax
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| 86 |
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| 87 | BS3_PROC_END_CMN Bs3ConvertRMStackToP16UsingCxReturnToAx
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| 88 |
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