VirtualBox

source: vbox/trunk/src/VBox/ValidationKit/bootsectors/bs3kit/bs3-cmn-SwitchTo16Bit.asm@ 66289

Last change on this file since 66289 was 64694, checked in by vboxsync, 8 years ago

bs3kit: Added Bs3SwitchTo32BitAndCallC and fixed a few problems switching from PE32 to other mode and back again.

  • Property svn:eol-style set to native
  • Property svn:keywords set to Author Date Id Revision
File size: 3.3 KB
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1; $Id: bs3-cmn-SwitchTo16Bit.asm 64694 2016-11-17 17:10:47Z vboxsync $
2;; @file
3; BS3Kit - Bs3SwitchTo16Bit
4;
5
6;
7; Copyright (C) 2007-2016 Oracle Corporation
8;
9; This file is part of VirtualBox Open Source Edition (OSE), as
10; available from http://www.virtualbox.org. This file is free software;
11; you can redistribute it and/or modify it under the terms of the GNU
12; General Public License (GPL) as published by the Free Software
13; Foundation, in version 2 as it comes in the "COPYING" file of the
14; VirtualBox OSE distribution. VirtualBox OSE is distributed in the
15; hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
16;
17; The contents of this file may alternatively be used under the terms
18; of the Common Development and Distribution License Version 1.0
19; (CDDL) only, as it comes in the "COPYING.CDDL" file of the
20; VirtualBox OSE distribution, in which case the provisions of the
21; CDDL are applicable instead of those of the GPL.
22;
23; You may elect to license modified versions of this file under the
24; terms and conditions of either the GPL or the CDDL or both.
25;
26
27%include "bs3kit-template-header.mac"
28
29BS3_EXTERN_DATA16 g_bBs3CurrentMode
30%if TMPL_BITS == 16
31BS3_EXTERN_CMN Bs3Syscall
32%endif
33TMPL_BEGIN_TEXT
34
35
36;;
37; @cproto BS3_DECL(void) Bs3SwitchTo16Bit(void);
38; @remarks Does not require 20h of parameter scratch space in 64-bit mode.
39;
40BS3_PROC_BEGIN_CMN Bs3SwitchTo16Bit, BS3_PBC_NEAR
41%if TMPL_BITS == 16
42 push ax
43 push ds
44
45 ; Check g_bBs3CurrentMode whether we're in v8086 mode or not.
46 mov al, [BS3_DATA16_WRT(g_bBs3CurrentMode)]
47 test al, BS3_MODE_CODE_V86
48 jz .ret_16bit
49
50 ; Switch to ring-0 if v8086 mode.
51 mov ax, BS3_SYSCALL_TO_RING0
52 call Bs3Syscall
53
54.ret_16bit:
55 pop ds
56 pop ax
57 ret
58
59%else
60 push xAX
61 push xBX
62 xPUSHF
63 cli
64
65 ; Calc new CS.
66 mov ax, cs
67 and xAX, 3
68 shl xAX, BS3_SEL_RING_SHIFT ; ring addend.
69 add xAX, BS3_SEL_R0_CS16
70
71 ; Construct a far return for switching to 16-bit code.
72 push xAX
73 push .sixteen_bit
74 xRETF
75
76BS3_BEGIN_TEXT16
77BS3_GLOBAL_LOCAL_LABEL .sixteen_bit
78
79 ; Load 16-bit segment registers.
80 add ax, BS3_SEL_R0_SS16 - BS3_SEL_R0_CS16
81 mov ss, ax
82
83 add ax, BS3_SEL_R0_DS16 - BS3_SEL_R0_SS16
84 mov ds, ax
85 mov es, ax
86
87 ; Thunk the stack if necessary.
88 mov ebx, esp
89 shr ebx, 16
90 jz .stack_ok
91int3 ; This is for later, just remove this int3 once needed.
92 test ax, X86_SEL_RPL
93 jnz .stack_rpl_must_be_0_for_custom_stacks
94 shl bx, X86_SEL_SHIFT
95 add bx, BS3_SEL_TILED
96 mov ss, bx
97 movzx esp, sp
98.stack_ok:
99
100 ; Update globals.
101 and byte [BS3_DATA16_WRT(g_bBs3CurrentMode)], ~BS3_MODE_CODE_MASK
102 or byte [BS3_DATA16_WRT(g_bBs3CurrentMode)], BS3_MODE_CODE_16
103
104 popfd
105TONLY64 pop ebx
106 pop ebx
107TONLY64 pop eax
108 pop eax
109TONLY64 add sp, 4
110 ret (TMPL_BITS - 16) / 8 ; Return and pop 2 or 6 bytes of "parameters" (unused return value)
111
112.stack_rpl_must_be_0_for_custom_stacks:
113 int3
114 jmp .stack_rpl_must_be_0_for_custom_stacks
115TMPL_BEGIN_TEXT
116%endif
117BS3_PROC_END_CMN Bs3SwitchTo16Bit
118
119;; @todo far 16-bit variant.
120
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