diff options
author | bxing <bxing@6f19259b-4bc3-4df7-8a09-765794883524> | 2007-01-10 06:57:04 +0000 |
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committer | bxing <bxing@6f19259b-4bc3-4df7-8a09-765794883524> | 2007-01-10 06:57:04 +0000 |
commit | a9a812a0ed4ab3d83941fdc6da281aebdb9bb296 (patch) | |
tree | 869ad144d2c1dcd96d859a9ac4c40617dfc96588 /MdePkg/Library/BaseLib/Ia32/Thunk16.asm | |
parent | 741fb364170375f89aa9c29488cc402db07a3776 (diff) | |
download | edk2-platforms-a9a812a0ed4ab3d83941fdc6da281aebdb9bb296.tar.xz |
1. Added comments to ASM files
2. Fixed a bug in 64-bit AsmDisablePaging64(), which may cause a #GP exception.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@2206 6f19259b-4bc3-4df7-8a09-765794883524
Diffstat (limited to 'MdePkg/Library/BaseLib/Ia32/Thunk16.asm')
-rw-r--r-- | MdePkg/Library/BaseLib/Ia32/Thunk16.asm | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/MdePkg/Library/BaseLib/Ia32/Thunk16.asm b/MdePkg/Library/BaseLib/Ia32/Thunk16.asm index 5e35799127..5c9bc81a2b 100644 --- a/MdePkg/Library/BaseLib/Ia32/Thunk16.asm +++ b/MdePkg/Library/BaseLib/Ia32/Thunk16.asm @@ -75,6 +75,11 @@ SavedGdt LABEL FWORD ; by user code. It will be shadowed to somewhere in memory below 1MB.
;------------------------------------------------------------------------------
_BackFromUserCode PROC
+ ;
+ ; The order of saved registers on the stack matches the order they appears
+ ; in IA32_REGS structure. This facilitates wrapper function to extract them
+ ; into that structure.
+ ;
push ss
push cs
DB 66h
@@ -104,6 +109,11 @@ _ThunkAttr DD ? mov eax, ss
DB 67h
lea bp, [esp + sizeof (IA32_REGS)]
+ ;
+ ; 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 word ptr (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._ESP, bp
mov ebx, (IA32_REGS ptr [esi - sizeof (IA32_REGS)])._EIP
shl ax, 4 ; shl eax, 4
@@ -167,7 +177,7 @@ _ToUserCode PROC pop fs
pop gs
popf ; popfd
- DB 66h
+ DB 66h ; Use 32-bit addressing for "retf" below
retf ; transfer control to user code
_ToUserCode ENDP
@@ -197,7 +207,7 @@ GdtEnd LABEL QWORD ; );
;------------------------------------------------------------------------------
InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs
- mov esi, [esp + 36] ; esi <- RegSet
+ mov esi, [esp + 36] ; esi <- RegSet, the 1st parameter
movzx edx, (IA32_REGS ptr [esi])._SS
mov edi, (IA32_REGS ptr [esi])._ESP
add edi, - (sizeof (IA32_REGS) + 4) ; reserve stack space
@@ -227,11 +237,11 @@ InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs push 10h
pop ecx ; ecx <- selector for data segments
lgdt fword ptr [edx + (_16Gdtr - SavedCr0)]
- pushfd
+ pushfd ; Save df/if indeed
call fword ptr [edx + (_EntryPoint - SavedCr0)]
popfd
lidt fword ptr [esp + 36] ; restore protected mode IDTR
- lea eax, [ebp - sizeof (IA32_REGS)]
+ lea eax, [ebp - sizeof (IA32_REGS)] ; eax <- the address of IA32_REGS
ret
InternalAsmThunk16 ENDP
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