+\r
+#include "BaseLibInternals.h"\r
+\r
;------------------------------------------------------------------------------\r
;\r
-; Copyright (c) 2006, Intel Corporation\r
-; All rights reserved. This program and the accompanying materials\r
+; Copyright (c) 2006 - 2013, Intel Corporation. All rights reserved.<BR>\r
+; This program and the accompanying materials\r
; are licensed and made available under the terms and conditions of the BSD License\r
; which accompanies this distribution. The full text of the license may be found at\r
-; http://opensource.org/licenses/bsd-license.php\r
+; http://opensource.org/licenses/bsd-license.php.\r
;\r
; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
EXTERNDEF C m16GdtrBase:WORD\r
EXTERNDEF C mTransition:WORD\r
\r
+;\r
+; Here is the layout of the real mode stack. _ToUserCode() is responsible for\r
+; loading all these registers from real mode stack.\r
+;\r
IA32_REGS STRUC 4t\r
_EDI DD ?\r
_ESI DD ?\r
\r
.const\r
\r
+;\r
+; These are global constant to convey information to C code.\r
+;\r
m16Size DW InternalAsmThunk16 - m16Start\r
mThunk16Attr DW _ThunkAttr - m16Start\r
m16Gdt DW _NullSegDesc - m16Start\r
SavedGdt LABEL FWORD\r
DW ?\r
DD ?\r
-\r
+;------------------------------------------------------------------------------\r
+; _BackFromUserCode() takes control in real mode after 'retf' has been executed\r
+; by user code. It will be shadowed to somewhere in memory below 1MB.\r
+;------------------------------------------------------------------------------\r
_BackFromUserCode PROC\r
+ ;\r
+ ; The order of saved registers on the stack matches the order they appears\r
+ ; in IA32_REGS structure. This facilitates wrapper function to extract them\r
+ ; into that structure.\r
+ ;\r
push ss\r
push cs\r
DB 66h\r
or al, 2\r
out 92h, al ; deactivate A20M#\r
@2:\r
- mov eax, ss\r
+ xor ax, ax ; xor eax, eax\r
+ mov eax, ss ; mov ax, ss\r
DB 67h\r
lea bp, [esp + sizeof (IA32_REGS)]\r
+ ;\r
+ ; esi's in the following 2 instructions are indeed bp in 16-bit code. Fact\r
+ ; is "esi" in 32-bit addressing mode has the same encoding of "bp" in 16-\r
+ ; bit addressing mode.\r
+ ;\r
mov word ptr (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._ESP, bp\r
mov ebx, (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._EIP\r
shl ax, 4 ; shl eax, 4\r
DW GdtEnd - _NullSegDesc - 1\r
_16GdtrBase DD _NullSegDesc\r
\r
+;------------------------------------------------------------------------------\r
+; _ToUserCode() takes control in real mode before passing control to user code.\r
+; It will be shadowed to somewhere in memory below 1MB.\r
+;------------------------------------------------------------------------------\r
_ToUserCode PROC\r
mov edx, ss\r
mov ss, ecx ; set new segment selectors\r
mov es, ecx\r
mov fs, ecx\r
mov gs, ecx\r
- mov cr0, eax\r
- mov cr4, ebp ; real mode starts at next instruction\r
+ mov cr0, eax ; real mode starts at next instruction\r
+ ; which (per SDM) *must* be a far JMP.\r
+ DB 0eah\r
+_RealAddr DW 0,0 ; filled in by InternalAsmThunk16\r
+\r
+ mov cr4, ebp\r
mov ss, esi ; set up 16-bit stack segment\r
xchg sp, bx ; set up 16-bit stack pointer\r
- DB 66h\r
- call @Base ; push eip\r
-@Base:\r
- pop bp ; ebp <- address of @Base\r
- DB 67h ; address size override\r
- push [esp + sizeof (IA32_REGS) + 2]\r
- lea eax, [esi + (@RealMode - @Base)]\r
- push eax\r
- retf\r
-@RealMode:\r
- mov cs:[esi + (SavedSs - @Base)], edx\r
- mov cs:[esi + (SavedEsp - @Base)], bx\r
- DB 66h\r
- lidt fword ptr cs:[esi + (_16Idtr - @Base)]\r
+\r
+; mov bp, [esp + sizeof(IA32_REGS)\r
+ DB 67h\r
+ mov ebp, [esp + sizeof(IA32_REGS)] ; BackFromUserCode address from stack\r
+\r
+; mov cs:[bp + (SavedSs - _BackFromUserCode)], dx\r
+ mov cs:[esi + (SavedSs - _BackFromUserCode)], edx\r
+\r
+; mov cs:[bp + (SavedEsp - _BackFromUserCode)], ebx\r
+ DB 2eh, 66h, 89h, 9eh\r
+ DW SavedEsp - _BackFromUserCode\r
+\r
+; lidt cs:[bp + (_16Idtr - _BackFromUserCode)]\r
+ DB 2eh, 66h, 0fh, 01h, 9eh\r
+ DW _16Idtr - _BackFromUserCode\r
+\r
popaw ; popad actually\r
pop ds\r
pop es\r
pop fs\r
pop gs\r
popf ; popfd\r
- DB 66h\r
+ DB 66h ; Use 32-bit addressing for "retf" below\r
retf ; transfer control to user code\r
_ToUserCode ENDP\r
\r
DB 0\r
GdtEnd LABEL QWORD\r
\r
-;\r
-; @param RegSet Pointer to a IA32_DWORD_REGS structure\r
-; @param Transition Pointer to the transition code\r
-; @return The address of the 16-bit stack after returning from user code\r
-;\r
+;------------------------------------------------------------------------------\r
+; IA32_REGISTER_SET *\r
+; EFIAPI\r
+; InternalAsmThunk16 (\r
+; IN IA32_REGISTER_SET *RegisterSet,\r
+; IN OUT VOID *Transition\r
+; );\r
+;------------------------------------------------------------------------------\r
InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs\r
- mov esi, [esp + 36] ; esi <- RegSet\r
+ mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter\r
movzx edx, (IA32_REGS ptr [esi])._SS\r
mov edi, (IA32_REGS ptr [esi])._ESP\r
add edi, - (sizeof (IA32_REGS) + 4) ; reserve stack space\r
lea ecx, [ecx + (_BackFromUserCode - m16Start)]\r
mov ax, cx\r
stosd ; [edi] <- return address of user code\r
+ add eax, _RealAddr + 4 - _BackFromUserCode\r
+ mov dword ptr [edx + (_RealAddr - SavedCr0)], eax\r
sgdt fword ptr [edx + (SavedGdt - SavedCr0)]\r
sidt fword ptr [esp + 36] ; save IDT stack in argument space\r
mov eax, cr0\r
and eax, 7ffffffeh ; clear PE, PG bits\r
mov ebp, cr4\r
mov [edx + (SavedCr4 - SavedCr0)], ebp\r
- and ebp, 300h ; clear all but PCE and OSFXSR bits\r
+ and ebp, NOT 30h ; clear PAE, PSE bits\r
push 10h\r
pop ecx ; ecx <- selector for data segments\r
lgdt fword ptr [edx + (_16Gdtr - SavedCr0)]\r
- pushfd\r
+ pushfd ; Save df/if indeed\r
call fword ptr [edx + (_EntryPoint - SavedCr0)]\r
popfd\r
lidt fword ptr [esp + 36] ; restore protected mode IDTR\r
- lea eax, [ebp - sizeof (IA32_REGS)]\r
+ lea eax, [ebp - sizeof (IA32_REGS)] ; eax <- the address of IA32_REGS\r
ret\r
InternalAsmThunk16 ENDP\r
\r
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