2 #include "BaseLibInternals.h"
4 ;------------------------------------------------------------------------------
6 ; Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>
7 ; This program and the accompanying materials
8 ; are licensed and made available under the terms and conditions of the BSD License
9 ; which accompanies this distribution. The full text of the license may be found at
10 ; http://opensource.org/licenses/bsd-license.php.
12 ; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
13 ; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
23 ;------------------------------------------------------------------------------
28 EXTERNDEF C m16Start:BYTE
29 EXTERNDEF C m16Size:WORD
30 EXTERNDEF C mThunk16Attr:WORD
31 EXTERNDEF C m16Gdt:WORD
32 EXTERNDEF C m16GdtrBase:WORD
33 EXTERNDEF C mTransition:WORD
36 ; Here is the layout of the real mode stack. _ToUserCode() is responsible for
37 ; loading all these registers from real mode stack.
61 ; These are global constant to convey information to C code.
63 m16Size DW InternalAsmThunk16 - m16Start
64 mThunk16Attr DW _ThunkAttr - m16Start
65 m16Gdt DW _NullSegDesc - m16Start
66 m16GdtrBase DW _16GdtrBase - m16Start
67 mTransition DW _EntryPoint - m16Start
76 ;------------------------------------------------------------------------------
77 ; _BackFromUserCode() takes control in real mode after 'retf' has been executed
78 ; by user code. It will be shadowed to somewhere in memory below 1MB.
79 ;------------------------------------------------------------------------------
80 _BackFromUserCode PROC
82 ; The order of saved registers on the stack matches the order they appears
83 ; in IA32_REGS structure. This facilitates wrapper function to extract them
84 ; into that structure.
91 pushf ; pushfd actually
92 cli ; disable interrupts
97 pushaw ; pushad actually
98 DB 66h, 0bah ; mov edx, imm32
100 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
102 mov eax, 15cd2401h ; mov ax, 2401h & int 15h
103 cli ; disable interrupts
106 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
110 out 92h, al ; deactivate A20M#
112 xor ax, ax ; xor eax, eax
113 mov eax, ss ; mov ax, ss
115 lea bp, [esp + sizeof (IA32_REGS)]
117 ; esi's in the following 2 instructions are indeed bp in 16-bit code. Fact
118 ; is "esi" in 32-bit addressing mode has the same encoding of "bp" in 16-
119 ; bit addressing mode.
121 mov word ptr (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._ESP, bp
122 mov ebx, (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._EIP
123 shl ax, 4 ; shl eax, 4
124 add bp, ax ; add ebp, eax
125 DB 66h, 0b8h ; mov eax, imm32
129 lgdt fword ptr cs:[edi + (SavedGdt - @Base)]
130 DB 66h, 0b8h ; mov eax, imm32
133 DB 0b8h ; mov ax, imm16
136 DB 66h, 0bch ; mov esp, imm32
139 retf ; return to protected mode
140 _BackFromUserCode ENDP
142 _EntryPoint DD _ToUserCode - m16Start
144 _16Idtr FWORD (1 SHL 10) - 1
146 DW GdtEnd - _NullSegDesc - 1
147 _16GdtrBase DD _NullSegDesc
149 ;------------------------------------------------------------------------------
150 ; _ToUserCode() takes control in real mode before passing control to user code.
151 ; It will be shadowed to somewhere in memory below 1MB.
152 ;------------------------------------------------------------------------------
155 mov ss, ecx ; set new segment selectors
160 mov cr0, eax ; real mode starts at next instruction
161 ; which (per SDM) *must* be a far JMP.
163 _RealAddr DW 0,0 ; filled in by InternalAsmThunk16
166 mov ss, esi ; set up 16-bit stack segment
167 xchg sp, bx ; set up 16-bit stack pointer
169 ; mov bp, [esp + sizeof(IA32_REGS)
171 mov ebp, [esp + sizeof(IA32_REGS)] ; BackFromUserCode address from stack
173 ; mov cs:[bp + (SavedSs - _BackFromUserCode)], dx
174 mov cs:[esi + (SavedSs - _BackFromUserCode)], edx
176 ; mov cs:[bp + (SavedEsp - _BackFromUserCode)], ebx
177 DB 2eh, 66h, 89h, 9eh
178 DW SavedEsp - _BackFromUserCode
180 ; lidt cs:[bp + (_16Idtr - _BackFromUserCode)]
181 DB 2eh, 66h, 0fh, 01h, 9eh
182 DW _16Idtr - _BackFromUserCode
184 popaw ; popad actually
190 DB 66h ; Use 32-bit addressing for "retf" below
191 retf ; transfer control to user code
195 _16CsDesc LABEL QWORD
200 DB 8fh ; 16-bit segment, 4GB limit
202 _16DsDesc LABEL QWORD
207 DB 8fh ; 16-bit segment, 4GB limit
211 ;------------------------------------------------------------------------------
212 ; IA32_REGISTER_SET *
214 ; InternalAsmThunk16 (
215 ; IN IA32_REGISTER_SET *RegisterSet,
216 ; IN OUT VOID *Transition
218 ;------------------------------------------------------------------------------
219 InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs
220 mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter
221 movzx edx, (IA32_REGS ptr [esi])._SS
222 mov edi, (IA32_REGS ptr [esi])._ESP
223 add edi, - (sizeof (IA32_REGS) + 4) ; reserve stack space
224 mov ebx, edi ; ebx <- stack offset
225 imul eax, edx, 16 ; eax <- edx * 16
226 push sizeof (IA32_REGS) / 4
227 add edi, eax ; edi <- linear address of 16-bit stack
229 rep movsd ; copy RegSet
230 mov eax, [esp + 40] ; eax <- address of transition code
231 mov esi, edx ; esi <- 16-bit stack segment
232 lea edx, [eax + (SavedCr0 - m16Start)]
236 lea ecx, [ecx + (_BackFromUserCode - m16Start)]
238 stosd ; [edi] <- return address of user code
239 add eax, _RealAddr + 4 - _BackFromUserCode
240 mov dword ptr [edx + (_RealAddr - SavedCr0)], eax
241 sgdt fword ptr [edx + (SavedGdt - SavedCr0)]
242 sidt fword ptr [esp + 36] ; save IDT stack in argument space
244 mov [edx], eax ; save CR0 in SavedCr0
245 and eax, 7ffffffeh ; clear PE, PG bits
247 mov [edx + (SavedCr4 - SavedCr0)], ebp
248 and ebp, NOT 30h ; clear PAE, PSE bits
250 pop ecx ; ecx <- selector for data segments
251 lgdt fword ptr [edx + (_16Gdtr - SavedCr0)]
252 pushfd ; Save df/if indeed
253 call fword ptr [edx + (_EntryPoint - SavedCr0)]
255 lidt fword ptr [esp + 36] ; restore protected mode IDTR
256 lea eax, [ebp - sizeof (IA32_REGS)] ; eax <- the address of IA32_REGS
258 InternalAsmThunk16 ENDP