diff options
Diffstat (limited to 'MdePkg/Library/BaseLib/Ia32/Thunk16.nasm')
| -rw-r--r-- | MdePkg/Library/BaseLib/Ia32/Thunk16.nasm | 81 |
1 files changed, 32 insertions, 49 deletions
diff --git a/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm b/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm index c00e3ab078..a1093e0107 100644 --- a/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm +++ b/MdePkg/Library/BaseLib/Ia32/Thunk16.nasm @@ -82,23 +82,24 @@ _BackFromUserCode: ; in IA32_REGS structure. This facilitates wrapper function to extract them
; into that structure.
;
+BITS 16
push ss
push cs
- DB 66h
- call .Base ; push eip
+o32 call dword .Base ; push eip
.Base:
- pushfw ; pushfd actually
+ pushfd
cli ; disable interrupts
push gs
push fs
push es
push ds
- pushaw ; pushad actually
+ pushad
DB 66h, 0bah ; mov edx, imm32
.ThunkAttr: dd 0
test dl, THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15
jz .1
- mov eax, 15cd2401h ; mov ax, 2401h & int 15h
+ mov ax, 2401h
+ int 15h
cli ; disable interrupts
jnc .2
.1:
@@ -108,24 +109,17 @@ _BackFromUserCode: or al, 2
out 92h, al ; deactivate A20M#
.2:
- xor ax, ax ; xor eax, eax
- mov eax, ss ; mov ax, ss
- DB 67h
- lea bp, [esp + IA32_REGS.size]
- ;
- ; esi's in the following 2 instructions are indeed bp in 16-bit code. Fact
- ; is "esi" in 32-bit addressing mode has the same encoding of "bp" in 16-
- ; bit addressing mode.
- ;
- mov [esi - IA32_REGS.size + IA32_REGS._ESP], bp
- mov ebx, [esi - IA32_REGS.size + IA32_REGS._EIP]
- shl ax, 4 ; shl eax, 4
- add bp, ax ; add ebp, eax
+ xor eax, eax
+ mov ax, ss
+ lea ebp, [esp + IA32_REGS.size]
+ mov [bp - IA32_REGS.size + IA32_REGS._ESP], ebp
+ mov bx, [bp - IA32_REGS.size + IA32_REGS._EIP]
+ shl eax, 4 ; shl eax, 4
+ add ebp, eax ; add ebp, eax
DB 66h, 0b8h ; mov eax, imm32
.SavedCr4: DD 0
mov cr4, eax
- DB 66h
- lgdt [cs:edi + (SavedGdt - .Base)]
+o32 lgdt [cs:bx + (SavedGdt - .Base)]
DB 66h, 0b8h ; mov eax, imm32
.SavedCr0: DD 0
mov cr0, eax
@@ -134,8 +128,7 @@ _BackFromUserCode: mov ss, eax
DB 66h, 0bch ; mov esp, imm32
.SavedEsp DD 0
- DB 66h
- retf ; return to protected mode
+o32 retf ; return to protected mode
_EntryPoint:
DD _ToUserCode - ASM_PFX(m16Start)
@@ -153,45 +146,34 @@ _16GdtrBase: ; It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_ToUserCode:
- mov edx, ss
- mov ss, ecx ; set new segment selectors
- mov ds, ecx
- mov es, ecx
- mov fs, ecx
- mov gs, ecx
+BITS 16
+ mov dx, ss
+ mov ss, cx ; set new segment selectors
+ mov ds, cx
+ mov es, cx
+ mov fs, cx
+ mov gs, cx
mov cr0, eax ; real mode starts at next instruction
; which (per SDM) *must* be a far JMP.
DB 0eah
.RealAddr: DW 0, 0
mov cr4, ebp
- mov ss, esi ; set up 16-bit stack segment
- xchg sp, bx ; set up 16-bit stack pointer
-
-; mov bp, [esp + sizeof(IA32_REGS)
- DB 67h
- mov ebp, [esp + IA32_REGS.size] ; BackFromUserCode address from stack
-
-; mov cs:[bp + (_BackFromUserCode.SavedSs - _BackFromUserCode)], dx
- mov [cs:esi + (_BackFromUserCode.SavedSs - _BackFromUserCode)], edx
+ mov ss, si ; set up 16-bit stack segment
+ xchg esp, ebx ; set up 16-bit stack pointer
+ mov bp, [esp + IA32_REGS.size]
+ mov [cs:bp + (_BackFromUserCode.SavedSs - _BackFromUserCode)], dx
+ mov [cs:bp + (_BackFromUserCode.SavedEsp - _BackFromUserCode)], ebx
+ lidt [cs:bp + (_16Idtr - _BackFromUserCode)]
-; mov cs:[bp + (_BackFromUserCode.SavedEsp - _BackFromUserCode)], ebx
- DB 2eh, 66h, 89h, 9eh
- DW _BackFromUserCode.SavedEsp - _BackFromUserCode
-
-; lidt cs:[bp + (_16Idtr - _BackFromUserCode)]
- DB 2eh, 66h, 0fh, 01h, 9eh
- DW _16Idtr - _BackFromUserCode
-
- popaw ; popad actually
+ popad
pop ds
pop es
pop fs
pop gs
- popfw ; popfd
+ popfd
- DB 66h ; Use 32-bit addressing for "retf" below
- retf ; transfer control to user code
+o32 retf ; transfer control to user code
ALIGN 16
_NullSegDesc DQ 0
@@ -221,6 +203,7 @@ GdtEnd: ;------------------------------------------------------------------------------
global ASM_PFX(InternalAsmThunk16)
ASM_PFX(InternalAsmThunk16):
+BITS 32
push ebp
push ebx
push esi
|