diff options
Diffstat (limited to 'MdePkg/Library/BaseLib/Ia32/Thunk16.asm')
| -rw-r--r-- | MdePkg/Library/BaseLib/Ia32/Thunk16.asm | 29 |
1 files changed, 23 insertions, 6 deletions
diff --git a/MdePkg/Library/BaseLib/Ia32/Thunk16.asm b/MdePkg/Library/BaseLib/Ia32/Thunk16.asm index 9fba03ac05..5e35799127 100644 --- a/MdePkg/Library/BaseLib/Ia32/Thunk16.asm +++ b/MdePkg/Library/BaseLib/Ia32/Thunk16.asm @@ -29,6 +29,10 @@ EXTERNDEF C m16Gdt:WORD EXTERNDEF C m16GdtrBase:WORD
EXTERNDEF C mTransition:WORD
+;
+; Here is the layout of the real mode stack. _ToUserCode() is responsible for
+; loading all these registers from real mode stack.
+;
IA32_REGS STRUC 4t
_EDI DD ?
_ESI DD ?
@@ -50,6 +54,9 @@ IA32_REGS ENDS .const
+;
+; These are global constant to convey information to C code.
+;
m16Size DW InternalAsmThunk16 - m16Start
mThunk16Attr DW _ThunkAttr - m16Start
m16Gdt DW _NullSegDesc - m16Start
@@ -63,7 +70,10 @@ m16Start LABEL BYTE SavedGdt LABEL FWORD
DW ?
DD ?
-
+;------------------------------------------------------------------------------
+; _BackFromUserCode() takes control in real mode after 'retf' has been executed
+; by user code. It will be shadowed to somewhere in memory below 1MB.
+;------------------------------------------------------------------------------
_BackFromUserCode PROC
push ss
push cs
@@ -122,6 +132,10 @@ _16Gdtr LABEL FWORD DW GdtEnd - _NullSegDesc - 1
_16GdtrBase DD _NullSegDesc
+;------------------------------------------------------------------------------
+; _ToUserCode() takes control in real mode before passing control to user code.
+; It will be shadowed to somewhere in memory below 1MB.
+;------------------------------------------------------------------------------
_ToUserCode PROC
mov edx, ss
mov ss, ecx ; set new segment selectors
@@ -174,11 +188,14 @@ _16DsDesc LABEL QWORD DB 0
GdtEnd LABEL QWORD
-;
-; @param RegSet Pointer to a IA32_DWORD_REGS structure
-; @param Transition Pointer to the transition code
-; @return The address of the 16-bit stack after returning from user code
-;
+;------------------------------------------------------------------------------
+; IA32_REGISTER_SET *
+; EFIAPI
+; InternalAsmThunk16 (
+; IN IA32_REGISTER_SET *RegisterSet,
+; IN OUT VOID *Transition
+; );
+;------------------------------------------------------------------------------
InternalAsmThunk16 PROC USES ebp ebx esi edi ds es fs gs
mov esi, [esp + 36] ; esi <- RegSet
movzx edx, (IA32_REGS ptr [esi])._SS
|