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 ;------------------------------------------------------------------------------
25 global ASM_PFX(m16Size)
26 global ASM_PFX(mThunk16Attr)
27 global ASM_PFX(m16Gdt)
28 global ASM_PFX(m16GdtrBase)
29 global ASM_PFX(mTransition)
30 global ASM_PFX(m16Start)
59 ; These are global constant to convey information to C code.
61 ASM_PFX(m16Size) DW InternalAsmThunk16 - ASM_PFX(m16Start)
62 ASM_PFX(mThunk16Attr) DW _BackFromUserCode.ThunkAttr - ASM_PFX(m16Start)
63 ASM_PFX(m16Gdt) DW _NullSegDesc - ASM_PFX(m16Start)
64 ASM_PFX(m16GdtrBase) DW _16GdtrBase - ASM_PFX(m16Start)
65 ASM_PFX(mTransition) DW _EntryPoint - ASM_PFX(m16Start)
75 ;------------------------------------------------------------------------------
76 ; _BackFromUserCode() takes control in real mode after 'retf' has been executed
77 ; by user code. It will be shadowed to somewhere in memory below 1MB.
78 ;------------------------------------------------------------------------------
81 ; The order of saved registers on the stack matches the order they appears
82 ; in IA32_REGS structure. This facilitates wrapper function to extract them
83 ; into that structure.
88 o32 call dword .Base ; push eip
91 cli ; disable interrupts
97 DB 66h, 0bah ; mov edx, imm32
99 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
103 cli ; disable interrupts
106 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
110 out 92h, al ; deactivate A20M#
114 lea ebp, [esp + IA32_REGS.size]
115 mov [bp - IA32_REGS.size + IA32_REGS._ESP], ebp
116 mov bx, [bp - IA32_REGS.size + IA32_REGS._EIP]
117 shl eax, 4 ; shl eax, 4
118 add ebp, eax ; add ebp, eax
119 DB 66h, 0b8h ; mov eax, imm32
122 o32 lgdt [cs:bx + (SavedGdt - .Base)]
123 DB 66h, 0b8h ; mov eax, imm32
126 DB 0b8h ; mov ax, imm16
129 DB 66h, 0bch ; mov esp, imm32
131 o32 retf ; return to protected mode
134 DD _ToUserCode - ASM_PFX(m16Start)
140 DW GdtEnd - _NullSegDesc - 1
144 ;------------------------------------------------------------------------------
145 ; _ToUserCode() takes control in real mode before passing control to user code.
146 ; It will be shadowed to somewhere in memory below 1MB.
147 ;------------------------------------------------------------------------------
151 mov ss, cx ; set new segment selectors
156 mov cr0, eax ; real mode starts at next instruction
157 ; which (per SDM) *must* be a far JMP.
162 mov ss, si ; set up 16-bit stack segment
163 xchg esp, ebx ; set up 16-bit stack pointer
164 mov bp, [esp + IA32_REGS.size]
165 mov [cs:bp + (_BackFromUserCode.SavedSs - _BackFromUserCode)], dx
166 mov [cs:bp + (_BackFromUserCode.SavedEsp - _BackFromUserCode)], ebx
167 lidt [cs:bp + (_16Idtr - _BackFromUserCode)]
176 o32 retf ; transfer control to user code
185 DB 8fh ; 16-bit segment, 4GB limit
192 DB 8fh ; 16-bit segment, 4GB limit
196 ;------------------------------------------------------------------------------
197 ; IA32_REGISTER_SET *
199 ; InternalAsmThunk16 (
200 ; IN IA32_REGISTER_SET *RegisterSet,
201 ; IN OUT VOID *Transition
203 ;------------------------------------------------------------------------------
204 global ASM_PFX(InternalAsmThunk16)
205 ASM_PFX(InternalAsmThunk16):
215 mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter
216 movzx edx, word [esi + IA32_REGS._SS]
217 mov edi, [esi + IA32_REGS._ESP]
218 add edi, - (IA32_REGS.size + 4) ; reserve stack space
219 mov ebx, edi ; ebx <- stack offset
220 imul eax, edx, 16 ; eax <- edx * 16
221 push IA32_REGS.size / 4
222 add edi, eax ; edi <- linear address of 16-bit stack
224 rep movsd ; copy RegSet
225 mov eax, [esp + 40] ; eax <- address of transition code
226 mov esi, edx ; esi <- 16-bit stack segment
227 lea edx, [eax + (_BackFromUserCode.SavedCr0 - ASM_PFX(m16Start))]
231 lea ecx, [ecx + (_BackFromUserCode - ASM_PFX(m16Start))]
233 stosd ; [edi] <- return address of user code
234 add eax, _ToUserCode.RealAddr + 4 - _BackFromUserCode
235 mov [edx + (_ToUserCode.RealAddr - _BackFromUserCode.SavedCr0)], eax
236 sgdt [edx + (SavedGdt - _BackFromUserCode.SavedCr0)]
237 sidt [esp + 36] ; save IDT stack in argument space
239 mov [edx], eax ; save CR0 in _BackFromUserCode.SavedCr0
240 and eax, 7ffffffeh ; clear PE, PG bits
242 mov [edx + (_BackFromUserCode.SavedCr4 - _BackFromUserCode.SavedCr0)], ebp
243 and ebp, ~30h ; clear PAE, PSE bits
245 pop ecx ; ecx <- selector for data segments
246 lgdt [edx + (_16Gdtr - _BackFromUserCode.SavedCr0)]
247 pushfd ; Save df/if indeed
248 call dword far [edx + (_EntryPoint - _BackFromUserCode.SavedCr0)]
250 lidt [esp + 36] ; restore protected mode IDTR
251 lea eax, [ebp - IA32_REGS.size] ; eax <- the address of IA32_REGS