1 2 #include "BaseLibInternals.h" 3 4 ;------------------------------------------------------------------------------ 5 ; 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. 11 ; 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. 14 ; 15 ; Module Name: 16 ; 17 ; Thunk.asm 18 ; 19 ; Abstract: 20 ; 21 ; Real mode thunk 22 ; 23 ;------------------------------------------------------------------------------ 24 25 .686p 26 .model flat,C 27 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 34 35 ; 36 ; Here is the layout of the real mode stack. _ToUserCode() is responsible for 37 ; loading all these registers from real mode stack. 38 ; 39 IA32_REGS STRUC 4t 40 _EDI DD ? 41 _ESI DD ? 42 _EBP DD ? 43 _ESP DD ? 44 _EBX DD ? 45 _EDX DD ? 46 _ECX DD ? 47 _EAX DD ? 48 _DS DW ? 49 _ES DW ? 50 _FS DW ? 51 _GS DW ? 52 _EFLAGS DD ? 53 _EIP DD ? 54 _CS DW ? 55 _SS DW ? 56 IA32_REGS ENDS 57 58 .const 59 60 ; 61 ; These are global constant to convey information to C code. 62 ; 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 68 69 .code 70 71 m16Start LABEL BYTE 72 73 SavedGdt LABEL FWORD 74 DW ? 75 DD ? 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 81 ; 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. 85 ; 86 push ss 87 push cs 88 DB 66h 89 call @Base ; push eip 90 @Base: 91 pushf ; pushfd actually 92 cli ; disable interrupts 93 push gs 94 push fs 95 push es 96 push ds 97 pushaw ; pushad actually 98 DB 66h, 0bah ; mov edx, imm32 99 _ThunkAttr DD ? 100 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15 101 jz @1 102 mov eax, 15cd2401h ; mov ax, 2401h & int 15h 103 cli ; disable interrupts 104 jnc @2 105 @1: 106 test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL 107 jz @2 108 in al, 92h 109 or al, 2 110 out 92h, al ; deactivate A20M# 111 @2: 112 xor ax, ax ; xor eax, eax 113 mov eax, ss ; mov ax, ss 114 DB 67h 115 lea bp, [esp + sizeof (IA32_REGS)] 116 ; 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. 120 ; 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 126 SavedCr4 DD ? 127 mov cr4, eax 128 DB 66h 129 lgdt fword ptr cs:[edi + (SavedGdt - @Base)] 130 DB 66h, 0b8h ; mov eax, imm32 131 SavedCr0 DD ? 132 mov cr0, eax 133 DB 0b8h ; mov ax, imm16 134 SavedSs DW ? 135 mov ss, eax 136 DB 66h, 0bch ; mov esp, imm32 137 SavedEsp DD ? 138 DB 66h 139 retf ; return to protected mode 140 _BackFromUserCode ENDP 141 142 _EntryPoint DD _ToUserCode - m16Start 143 DW 8h 144 _16Idtr FWORD (1 SHL 10) - 1 145 _16Gdtr LABEL FWORD 146 DW GdtEnd - _NullSegDesc - 1 147 _16GdtrBase DD _NullSegDesc 148 149 ;------------------------------------------------------------------------------ 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 ;------------------------------------------------------------------------------ 153 _ToUserCode PROC 154 mov edx, ss 155 mov ss, ecx ; set new segment selectors 156 mov ds, ecx 157 mov es, ecx 158 mov fs, ecx 159 mov gs, ecx 160 mov cr0, eax ; real mode starts at next instruction 161 ; which (per SDM) *must* be a far JMP. 162 DB 0eah 163 _RealAddr DW 0,0 ; filled in by InternalAsmThunk16 164 165 mov cr4, ebp 166 mov ss, esi ; set up 16-bit stack segment 167 xchg sp, bx ; set up 16-bit stack pointer 168 169 ; mov bp, [esp + sizeof(IA32_REGS) 170 DB 67h 171 mov ebp, [esp + sizeof(IA32_REGS)] ; BackFromUserCode address from stack 172 173 ; mov cs:[bp + (SavedSs - _BackFromUserCode)], dx 174 mov cs:[esi + (SavedSs - _BackFromUserCode)], edx 175 176 ; mov cs:[bp + (SavedEsp - _BackFromUserCode)], ebx 177 DB 2eh, 66h, 89h, 9eh 178 DW SavedEsp - _BackFromUserCode 179 180 ; lidt cs:[bp + (_16Idtr - _BackFromUserCode)] 181 DB 2eh, 66h, 0fh, 01h, 9eh 182 DW _16Idtr - _BackFromUserCode 183 184 popaw ; popad actually 185 pop ds 186 pop es 187 pop fs 188 pop gs 189 popf ; popfd 190 DB 66h ; Use 32-bit addressing for "retf" below 191 retf ; transfer control to user code 192 _ToUserCode ENDP 193 194 _NullSegDesc DQ 0 195 _16CsDesc LABEL QWORD 196 DW -1 197 DW 0 198 DB 0 199 DB 9bh 200 DB 8fh ; 16-bit segment, 4GB limit 201 DB 0 202 _16DsDesc LABEL QWORD 203 DW -1 204 DW 0 205 DB 0 206 DB 93h 207 DB 8fh ; 16-bit segment, 4GB limit 208 DB 0 209 GdtEnd LABEL QWORD 210 211 ;------------------------------------------------------------------------------ 212 ; IA32_REGISTER_SET * 213 ; EFIAPI 214 ; InternalAsmThunk16 ( 215 ; IN IA32_REGISTER_SET *RegisterSet, 216 ; IN OUT VOID *Transition 217 ; ); 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 228 pop ecx 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)] 233 mov ecx, eax 234 and ecx, 0fh 235 shl eax, 12 236 lea ecx, [ecx + (_BackFromUserCode - m16Start)] 237 mov ax, cx 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 243 mov eax, cr0 244 mov [edx], eax ; save CR0 in SavedCr0 245 and eax, 7ffffffeh ; clear PE, PG bits 246 mov ebp, cr4 247 mov [edx + (SavedCr4 - SavedCr0)], ebp 248 and ebp, NOT 30h ; clear PAE, PSE bits 249 push 10h 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)] 254 popfd 255 lidt fword ptr [esp + 36] ; restore protected mode IDTR 256 lea eax, [ebp - sizeof (IA32_REGS)] ; eax <- the address of IA32_REGS 257 ret 258 InternalAsmThunk16 ENDP 259 260 END 261
