I fixed following bugs in EDKII.

1. In AsmFuncs.asm, DebugSupport, Vect2Desc() function will use hardcode CS to fill the IDT. 20h for Ia32.If the system CS is changed by CPU driver, this driver can not work. System maybe crash.
2. In EBC, RegisterExceptionCallback() can not restore the environment and I add some enhancements.
3. In Image.c, CoreLoadImageCommon never return EFI_SECURITY_VIOLATION when SecurityStatus == EFI_SECURITY_VIOLATION.
4. In Variable.c, 1. There're additional unnecessary loop. All blocks will be gone through even if all the data has been written. We should check the "CurrWriteSize" to see if there's no more data to write, and stop the for loop immediately. 2 "if.else." can be merged to save lines of code.
5. in FvbServices,c, Checksum calculation error.


git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@1891 6f19259b-4bc3-4df7-8a09-765794883524

EdkModulePkg/Universal/DebugSupport/Dxe/Ia32/AsmFuncs.asm

@@ -189,7 +189,8 @@ Vect2Desc       PROC    C PUBLIC DestPtr:DWORD, Vector:DWORD
                 mov     eax, Vector
                 mov     ecx, DestPtr
                 mov     word ptr [ecx], ax                  ; write bits 15..0 of offset
-                mov     word ptr [ecx+2], 20h               ; SYS_CODE_SEL from GDT
+                mov     dx, cs
+                mov     word ptr [ecx+2], dx                ; SYS_CODE_SEL from GDT
                 mov     word ptr [ecx+4], 0e00h OR 8000h    ; type = 386 interrupt gate, present
                 shr     eax, 16
                 mov     word ptr [ecx+6], ax                ; write bits 31..16 of offset