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 ASM_PFX(InternalAsmThunk16) - ASM_PFX(m16Start)
62 ASM_PFX(mThunk16Attr) DW _BackFromUserCode.ThunkAttrEnd - 4 - 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.
89 ; Note: We can't use o32 on the next instruction because of a bug
90 ; in NASM 2.09.04 through 2.10rc1.
92 call dword .Base ; push eip
95 cli ; disable interrupts
101 mov edx, strict dword 0
103 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
107 cli ; disable interrupts
110 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL
114 out 92h, al ; deactivate A20M#
118 lea ebp, [esp + IA32_REGS.size]
119 mov [bp - IA32_REGS.size + IA32_REGS._ESP], ebp
120 mov bx, [bp - IA32_REGS.size + IA32_REGS._EIP]
121 shl eax, 4 ; shl eax, 4
122 add ebp, eax ; add ebp, eax
123 mov eax, strict dword 0
126 o32 lgdt [cs:bx + (SavedGdt - .Base)]
127 mov eax, strict dword 0
130 mov ax, strict word 0
133 mov esp, strict dword 0
135 o32 retf ; return to protected mode
138 DD _ToUserCode - ASM_PFX(m16Start)
144 DW GdtEnd - _NullSegDesc - 1
148 ;------------------------------------------------------------------------------
149 ; _ToUserCode() takes control in real mode before passing control to user code.
150 ; It will be shadowed to somewhere in memory below 1MB.
151 ;------------------------------------------------------------------------------
155 mov ss, cx ; set new segment selectors
160 mov cr0, eax ; real mode starts at next instruction
161 ; which (per SDM) *must* be a far JMP.
165 mov ss, si ; set up 16-bit stack segment
166 xchg esp, ebx ; set up 16-bit stack pointer
167 mov bp, [esp + IA32_REGS.size]
168 mov [cs:bp + (_BackFromUserCode.SavedSsEnd - 2 - _BackFromUserCode)], dx
169 mov [cs:bp + (_BackFromUserCode.SavedEspEnd - 4 - _BackFromUserCode)], ebx
170 lidt [cs:bp + (_16Idtr - _BackFromUserCode)]
179 o32 retf ; transfer control to user code
188 DB 8fh ; 16-bit segment, 4GB limit
195 DB 8fh ; 16-bit segment, 4GB limit
199 ;------------------------------------------------------------------------------
200 ; IA32_REGISTER_SET *
202 ; InternalAsmThunk16 (
203 ; IN IA32_REGISTER_SET *RegisterSet,
204 ; IN OUT VOID *Transition
206 ;------------------------------------------------------------------------------
207 global ASM_PFX(InternalAsmThunk16)
208 ASM_PFX(InternalAsmThunk16):
218 mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter
219 movzx edx, word [esi + IA32_REGS._SS]
220 mov edi, [esi + IA32_REGS._ESP]
221 add edi, - (IA32_REGS.size + 4) ; reserve stack space
222 mov ebx, edi ; ebx <- stack offset
223 imul eax, edx, 16 ; eax <- edx * 16
224 push IA32_REGS.size / 4
225 add edi, eax ; edi <- linear address of 16-bit stack
227 rep movsd ; copy RegSet
228 mov eax, [esp + 40] ; eax <- address of transition code
229 mov esi, edx ; esi <- 16-bit stack segment
230 lea edx, [eax + (_BackFromUserCode.SavedCr0End - ASM_PFX(m16Start))]
234 lea ecx, [ecx + (_BackFromUserCode - ASM_PFX(m16Start))]
236 stosd ; [edi] <- return address of user code
237 add eax, _ToUserCode.RealAddrEnd - _BackFromUserCode
238 mov [edx + (_ToUserCode.RealAddrEnd - 4 - _BackFromUserCode.SavedCr0End)], eax
239 sgdt [edx + (SavedGdt - _BackFromUserCode.SavedCr0End)]
240 sidt [esp + 36] ; save IDT stack in argument space
242 mov [edx - 4], eax ; save CR0 in _BackFromUserCode.SavedCr0End - 4
243 and eax, 7ffffffeh ; clear PE, PG bits
245 mov [edx + (_BackFromUserCode.SavedCr4End - 4 - _BackFromUserCode.SavedCr0End)], ebp
246 and ebp, ~30h ; clear PAE, PSE bits
248 pop ecx ; ecx <- selector for data segments
249 lgdt [edx + (_16Gdtr - _BackFromUserCode.SavedCr0End)]
250 pushfd ; Save df/if indeed
251 call dword far [edx + (_EntryPoint - _BackFromUserCode.SavedCr0End)]
253 lidt [esp + 36] ; restore protected mode IDTR
254 lea eax, [ebp - IA32_REGS.size] ; eax <- the address of IA32_REGS