Index: BaseTools/Conf/tools_def.template
===================================================================
--- BaseTools/Conf/tools_def.template	(revision 16254)
+++ BaseTools/Conf/tools_def.template	(working copy)
@@ -3843,7 +3843,7 @@
 
 DEFINE GCC44_ALL_CC_FLAGS            = -g -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-array-bounds -ffunction-sections -fdata-sections -c -include AutoGen.h -DSTRING_ARRAY_NAME=$(BASE_NAME)Strings
 DEFINE GCC44_IA32_CC_FLAGS           = DEF(GCC44_ALL_CC_FLAGS) -m32 -malign-double -fno-stack-protector -D EFI32
-DEFINE GCC44_X64_CC_FLAGS            = DEF(GCC44_ALL_CC_FLAGS) -m64 -fno-stack-protector "-DEFIAPI=__attribute__((ms_abi))" -DNO_BUILTIN_VA_FUNCS -mno-red-zone -Wno-address -mcmodel=large
+DEFINE GCC44_X64_CC_FLAGS            = DEF(GCC44_ALL_CC_FLAGS) -m64 -fno-stack-protector "-DEFIAPI=__attribute__((ms_abi))" -mno-red-zone -Wno-address -mcmodel=large
 DEFINE GCC44_IA32_X64_DLINK_COMMON   = -nostdlib -n -q --gc-sections --script=$(EDK_TOOLS_PATH)/Scripts/gcc4.4-ld-script
 DEFINE GCC44_IA32_X64_ASLDLINK_FLAGS = DEF(GCC44_IA32_X64_DLINK_COMMON) --entry ReferenceAcpiTable -u ReferenceAcpiTable
 DEFINE GCC44_IA32_X64_DLINK_FLAGS    = DEF(GCC44_IA32_X64_DLINK_COMMON) --entry $(IMAGE_ENTRY_POINT) -u $(IMAGE_ENTRY_POINT) -Map $(DEST_DIR_DEBUG)/$(BASE_NAME).map
@@ -4420,7 +4420,7 @@
 *_GCC48_X64_ASLCC_FLAGS          = DEF(GCC_ASLCC_FLAGS) -m64
 *_GCC48_X64_ASLDLINK_FLAGS       = DEF(GCC48_IA32_X64_ASLDLINK_FLAGS) -m elf_x86_64
 *_GCC48_X64_ASM_FLAGS            = DEF(GCC48_ASM_FLAGS) -m64
-*_GCC48_X64_CC_FLAGS             = DEF(GCC48_X64_CC_FLAGS)
+*_GCC48_X64_CC_FLAGS             = DEF(GCC48_X64_CC_FLAGS) -Os
 *_GCC48_X64_DLINK_FLAGS          = DEF(GCC48_X64_DLINK_FLAGS)
 *_GCC48_X64_RC_FLAGS             = DEF(GCC_X64_RC_FLAGS)
 *_GCC48_X64_OBJCOPY_FLAGS        = 
@@ -4542,7 +4542,7 @@
 *_GCC49_X64_ASLCC_FLAGS          = DEF(GCC_ASLCC_FLAGS) -m64
 *_GCC49_X64_ASLDLINK_FLAGS       = DEF(GCC49_IA32_X64_ASLDLINK_FLAGS) -m elf_x86_64
 *_GCC49_X64_ASM_FLAGS            = DEF(GCC49_ASM_FLAGS) -m64
-*_GCC49_X64_CC_FLAGS             = DEF(GCC49_X64_CC_FLAGS)
+*_GCC49_X64_CC_FLAGS             = DEF(GCC49_X64_CC_FLAGS) -Os
 *_GCC49_X64_DLINK_FLAGS          = DEF(GCC49_X64_DLINK_FLAGS)
 *_GCC49_X64_RC_FLAGS             = DEF(GCC_X64_RC_FLAGS)
 *_GCC49_X64_OBJCOPY_FLAGS        = 
Index: EdkCompatibilityPkg/Foundation/Include/EfiStdArg.h
===================================================================
--- EdkCompatibilityPkg/Foundation/Include/EfiStdArg.h	(revision 16254)
+++ EdkCompatibilityPkg/Foundation/Include/EfiStdArg.h	(working copy)
@@ -66,6 +66,7 @@
   @return The aligned size.
 **/
 #define _INT_SIZE_OF(n) ((sizeof (n) + sizeof (UINTN) - 1) &~(sizeof (UINTN) - 1))
+#define GCC_VERSION (__GNUC__ * 10 + __GNUC_MINOR__)
 
 #if defined(__CC_ARM)
 //
@@ -92,25 +93,37 @@
 
 #define VA_COPY(Dest, Start)          __va_copy (Dest, Start)
 
-#elif defined(__GNUC__) && !defined(NO_BUILTIN_VA_FUNCS)
+#elif defined(__GNUC__) && !defined(__x86_64__)
 //
 // Use GCC built-in macros for variable argument lists.
 //
 
 ///
-/// Variable used to traverse the list of arguments. This type can vary by 
-/// implementation and could be an array or structure. 
+/// Variable used to traverse the list of arguments. This type can vary by
+/// implementation and could be an array or structure.
 ///
-typedef __builtin_va_list VA_LIST;
+  typedef __builtin_va_list VA_LIST;
 
-#define VA_START(Marker, Parameter)  __builtin_va_start (Marker, Parameter)
+  #define VA_START(Marker, Parameter)  __builtin_va_start (Marker, Parameter)
 
-#define VA_ARG(Marker, TYPE)         ((sizeof (TYPE) < sizeof (UINTN)) ? (TYPE)(__builtin_va_arg (Marker, UINTN)) : (TYPE)(__builtin_va_arg (Marker, TYPE)))
+  #define VA_ARG(Marker, TYPE)         ((sizeof (TYPE) < sizeof (UINTN)) ? (TYPE)(__builtin_va_arg (Marker, UINTN)) : (TYPE)(__builtin_va_arg (Marker, TYPE)))
 
-#define VA_END(Marker)               __builtin_va_end (Marker)
+  #define VA_END(Marker)               __builtin_va_end (Marker)
 
-#define VA_COPY(Dest, Start)         __builtin_va_copy (Dest, Start)
+  #define VA_COPY(Dest, Start)         __builtin_va_copy (Dest, Start)
 
+#elif defined(__GNUC__) && defined(__x86_64__) && (GCC_VERSION >= 48)
+
+  typedef __builtin_ms_va_list VA_LIST;
+
+  #define VA_START(Marker, Parameter)  __builtin_ms_va_start (Marker, Parameter)
+
+  #define VA_ARG(Marker, TYPE)         ((sizeof (TYPE) < sizeof (UINTN)) ? (TYPE)(__builtin_va_arg (Marker, UINTN)) : (TYPE)(__builtin_va_arg (Marker, TYPE)))
+
+  #define VA_END(Marker)               __builtin_ms_va_end (Marker)
+
+  #define VA_COPY(Dest, Start)         __builtin_ms_va_copy (Dest, Start)
+
 #else
 
 #ifndef VA_START
Index: MdePkg/Include/Base.h
===================================================================
--- MdePkg/Include/Base.h	(revision 16254)
+++ MdePkg/Include/Base.h	(working copy)
@@ -441,6 +441,7 @@
   @return The aligned size.
 **/
 #define _INT_SIZE_OF(n) ((sizeof (n) + sizeof (UINTN) - 1) &~(sizeof (UINTN) - 1))
+#define GCC_VERSION (__GNUC__ * 10 + __GNUC_MINOR__)
 
 #if defined(__CC_ARM)
 //
@@ -472,7 +473,7 @@
 
 #define VA_COPY(Dest, Start)          __va_copy (Dest, Start)
 
-#elif defined(__GNUC__) && !defined(NO_BUILTIN_VA_FUNCS)
+#elif defined(__GNUC__) && !defined(__x86_64__)
 //
 // Use GCC built-in macros for variable argument lists.
 //
@@ -481,16 +482,28 @@
 /// Variable used to traverse the list of arguments. This type can vary by
 /// implementation and could be an array or structure.
 ///
-typedef __builtin_va_list VA_LIST;
+  typedef __builtin_va_list VA_LIST;
 
-#define VA_START(Marker, Parameter)  __builtin_va_start (Marker, Parameter)
+  #define VA_START(Marker, Parameter)  __builtin_va_start (Marker, Parameter)
 
-#define VA_ARG(Marker, TYPE)         ((sizeof (TYPE) < sizeof (UINTN)) ? (TYPE)(__builtin_va_arg (Marker, UINTN)) : (TYPE)(__builtin_va_arg (Marker, TYPE)))
+  #define VA_ARG(Marker, TYPE)         ((sizeof (TYPE) < sizeof (UINTN)) ? (TYPE)(__builtin_va_arg (Marker, UINTN)) : (TYPE)(__builtin_va_arg (Marker, TYPE)))
 
-#define VA_END(Marker)               __builtin_va_end (Marker)
+  #define VA_END(Marker)               __builtin_va_end (Marker)
 
-#define VA_COPY(Dest, Start)         __builtin_va_copy (Dest, Start)
+  #define VA_COPY(Dest, Start)         __builtin_va_copy (Dest, Start)
 
+#elif defined(__GNUC__) && defined(__x86_64__) && (GCC_VERSION >= 48)
+
+  typedef __builtin_ms_va_list VA_LIST;
+
+  #define VA_START(Marker, Parameter)  __builtin_ms_va_start (Marker, Parameter)
+
+  #define VA_ARG(Marker, TYPE)         ((sizeof (TYPE) < sizeof (UINTN)) ? (TYPE)(__builtin_va_arg (Marker, UINTN)) : (TYPE)(__builtin_va_arg (Marker, TYPE)))
+
+  #define VA_END(Marker)               __builtin_ms_va_end (Marker)
+
+  #define VA_COPY(Dest, Start)         __builtin_ms_va_copy (Dest, Start)
+
 #else
 ///
 /// Variable used to traverse the list of arguments. This type can vary by