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MdePkg BaseLib NASM Thunk16: Use bits 16 for 16-bit code

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By using 'bits 16', we can write code for 16-bit use the actual
assembly syntax rather than 'DB' and sometimes writing code with
seemingly incorrect operands because we know it will run correctly
when the processor is running in 16-bit mode.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16023 6f19259b-4bc3-4df7-8a09-765794883524
This commit is contained in:
Jordan Justen
2014-09-01 17:23:51 +00:00
committed by jljusten
parent a8458d6cb3
commit f6888eea46
2 changed files with 87 additions and 115 deletions
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81
MdePkg/Library/BaseLib/Ia32/Thunk16.nasm
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@@ -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 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 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 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