BaseUefiCpuLib: Preserve EBX register in InitializeFloatingPointUnits

The EBX register should be preserved for the IA32 C calling convention.
The use of the CPUID instruction was modifying the EBX register, so
we push and pop EBX.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9573 6f19259b-4bc3-4df7-8a09-765794883524

UefiCpuPkg/Library/BaseUefiCpuLib/Ia32/InitializeFpu.S

@@ -35,6 +35,9 @@ ASM_PFX(mMmxControlWord): .long     0x01F80
 #
 ASM_GLOBAL ASM_PFX(InitializeFloatingPointUnits)
 ASM_PFX(InitializeFloatingPointUnits):
+
+    pushl   %ebx
+
     #
     # Initialize floating point units
     #
@@ -64,6 +67,8 @@ ASM_PFX(InitializeFloatingPointUnits):
     ldmxcsr ASM_PFX(mMmxControlWord)
 
 Done:
+    popl    %ebx
+
     ret
 
 #END

UefiCpuPkg/Library/BaseUefiCpuLib/Ia32/InitializeFpu.asm

@@ -39,6 +39,9 @@ mMmxControlWord       DD      01F80h
 ; for masked underflow).
 ;
 InitializeFloatingPointUnits PROC PUBLIC
+
+    push    ebx
+
     ;
     ; Initialize floating point units
     ;
@@ -67,6 +70,7 @@ InitializeFloatingPointUnits PROC PUBLIC
     ;
     ldmxcsr mMmxControlWord
 Done:
+    pop     ebx
 
     ret