From f6888eea465a8e293cb46b56c16f9f63eed43f3d Mon Sep 17 00:00:00 2001 From: Jordan Justen Date: Mon, 1 Sep 2014 17:23:51 +0000 Subject: MdePkg BaseLib NASM Thunk16: Use bits 16 for 16-bit code 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 Reviewed-by: Liming Gao git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16023 6f19259b-4bc3-4df7-8a09-765794883524 --- MdePkg/Library/BaseLib/Ia32/Thunk16.nasm | 81 +++++++++++++------------------- 1 file changed, 32 insertions(+), 49 deletions(-) (limited to 'MdePkg/Library/BaseLib/Ia32') 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 -- cgit v1.2.3