| 1 | ; $Id: bs3-cmn-SwitchTo16Bit.asm 59242 2016-01-03 01:09:38Z vboxsync $
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| 2 | ;; @file
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| 3 | ; BS3Kit - Bs3SwitchTo16Bit
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| 4 | ;
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| 5 |
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| 6 | ;
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| 7 | ; Copyright (C) 2007-2015 Oracle Corporation
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| 8 | ;
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| 9 | ; This file is part of VirtualBox Open Source Edition (OSE), as
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| 10 | ; available from http://www.virtualbox.org. This file is free software;
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| 11 | ; you can redistribute it and/or modify it under the terms of the GNU
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| 12 | ; General Public License (GPL) as published by the Free Software
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| 13 | ; Foundation, in version 2 as it comes in the "COPYING" file of the
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| 14 | ; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
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| 15 | ; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
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| 16 | ;
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| 17 | ; The contents of this file may alternatively be used under the terms
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| 18 | ; of the Common Development and Distribution License Version 1.0
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| 19 | ; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
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| 20 | ; VirtualBox OSE distribution, in which case the provisions of the
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| 21 | ; CDDL are applicable instead of those of the GPL.
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| 22 | ;
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| 23 | ; You may elect to license modified versions of this file under the
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| 24 | ; terms and conditions of either the GPL or the CDDL or both.
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| 25 | ;
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| 26 |
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| 27 | %include "bs3kit-template-header.mac"
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| 28 |
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| 29 | ;;
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| 30 | ; @cproto BS3_DECL(void) Bs3SwitchTo16Bit(void);
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| 31 | ;
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| 32 | BS3_PROC_BEGIN_CMN Bs3SwitchTo16Bit
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| 33 | %if TMPL_BITS == 16
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| 34 | ret
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| 35 | %else
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| 36 | push xAX
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| 37 | xPUSHF
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| 38 | cli
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| 39 |
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| 40 | ; Calc new CS.
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| 41 | mov ax, cs
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| 42 | and xAX, 3
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| 43 | shl xAX, BS3_SEL_RING_SHIFT ; ring addend.
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| 44 | add xAX, BS3_SEL_R0_CS16
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| 45 |
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| 46 | ; Construct a far return for switching to 16-bit code.
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| 47 | push xAX
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| 48 | push .sixteen_bit
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| 49 | xRETF
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| 50 |
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| 51 | BS3_BEGIN_TEXT16
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| 52 | .sixteen_bit:
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| 53 | ; Load 16-bit segment registers.
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| 54 | ;; @todo support non-standard stacks?
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| 55 | add ax, BS3_SEL_R0_SS16 - BS3_SEL_R0_CS16
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| 56 | mov ss, ax
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| 57 |
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| 58 | add ax, BS3_SEL_R0_DS16 - BS3_SEL_R0_SS16
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| 59 | mov ds, ax
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| 60 | mov es, ax
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| 61 |
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| 62 | popfd
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| 63 | %if TMPL_BITS == 64
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| 64 | add sp, 4
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| 65 | %endif
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| 66 | pop eax
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| 67 | %if TMPL_BITS == 64
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| 68 | add sp, 4
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| 69 | %endif
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| 70 | ret sCB - 2 ; Return and pop 2 or 6 bytes of "parameters" (unused return value)
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| 71 | TMPL_BEGIN_TEXT
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| 72 | %endif
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| 73 | BS3_PROC_END_CMN Bs3SwitchTo16Bit
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| 74 |
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