kbuild: Fix clang detection

We cannot detect clang before including the arch Makefile, because that
can set the default cross compiler. We also cannot detect clang after
including the arch Makefile, because powerpc wants to know about clang.
Solve this by using an deferred variable. This costs us a few shell
invocations, but this is only a constant number.
Reported-by: Behan Webster <behanw@converseincode.com>
Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michal Marek <mmarek@suse.com>

Makefile

@@ -661,14 +661,7 @@ endif
 endif
 KBUILD_CFLAGS += $(stackp-flag)
 
-ifeq ($(shell $(CC) -v 2>&1 | grep -c "clang version"), 1)
-COMPILER := clang
-else
-COMPILER := gcc
-endif
-export COMPILER
-
-ifeq ($(COMPILER),clang)
+ifeq ($(cc-name),clang)
 KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
 KBUILD_CPPFLAGS += $(call cc-option,-Wno-unknown-warning-option,)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)

arch/powerpc/Makefile

@@ -67,7 +67,7 @@ UTS_MACHINE := $(OLDARCH)
 
 ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
 override CC	+= -mlittle-endian
-ifneq ($(COMPILER),clang)
+ifneq ($(cc-name),clang)
 override CC	+= -mno-strict-align
 endif
 override AS	+= -mlittle-endian
@@ -333,7 +333,7 @@ TOUT	:= .tmp_gas_check
 # - Require gcc 4.0 or above on 64-bit
 # - gcc-4.2.0 has issues compiling modules on 64-bit
 checkbin:
-	@if test "${COMPILER}" != "clang" \
+	@if test "$(cc-name)" != "clang" \
 	    && test "$(cc-version)" = "0304" ; then \
 		if ! /bin/echo mftb 5 | $(AS) -v -mppc -many -o $(TOUT) >/dev/null 2>&1 ; then \
 			echo -n '*** ${VERSION}.${PATCHLEVEL} kernels no longer build '; \
@@ -342,14 +342,14 @@ checkbin:
 			false; \
 		fi ; \
 	fi
-	@if test "${COMPILER}" != "clang" \
+	@if test "$(cc-name)" != "clang" \
 	    && test "$(cc-version)" -lt "0400" \
 	    && test "x${CONFIG_PPC64}" = "xy" ; then \
                 echo -n "Sorry, GCC v4.0 or above is required to build " ; \
                 echo "the 64-bit powerpc kernel." ; \
                 false ; \
         fi
-	@if test "${COMPILER}" != "clang" \
+	@if test "$(cc-name)" != "clang" \
 	    && test "$(cc-fullversion)" = "040200" \
 	    && test "x${CONFIG_MODULES}${CONFIG_PPC64}" = "xyy" ; then \
 		echo -n '*** GCC-4.2.0 cannot compile the 64-bit powerpc ' ; \

scripts/Kbuild.include

@@ -128,6 +128,10 @@ cc-option-align = $(subst -functions=0,,\
 cc-disable-warning = $(call try-run,\
 	$(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -W$(strip $(1)) -c -x c /dev/null -o "$$TMP",-Wno-$(strip $(1)))
 
+# cc-name
+# Expands to either gcc or clang
+cc-name = $(shell $(CC) -v 2>&1 | grep -q "clang version" && echo clang || echo gcc)
+
 # cc-version
 cc-version = $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
 

scripts/Makefile.extrawarn

@@ -56,7 +56,7 @@ endif
 KBUILD_CFLAGS += $(warning)
 else
 
-ifeq ($(COMPILER),clang)
+ifeq ($(cc-name),clang)
 KBUILD_CFLAGS += $(call cc-disable-warning, initializer-overrides)
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-value)
 KBUILD_CFLAGS += $(call cc-disable-warning, format)