kbuild: Consolidated cc support function

Added three function to top-level Makefile:
cc-option (replacing check_gcc)
cc-option-yn (as cc-option but return y or n)
cc-version (numeric version of $(CC))
Documentation added to Documentation/kbuild/makefiles.txt

The check_gcc version is still present, but now spit out a arning if used.
The new naming where chosen to get consistent naming of all three functions
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Documentation/kbuild/makefiles.txt

@@ -37,6 +37,8 @@ This document describes the Linux kernel Makefiles.
 	   --- 6.5 Building non-kbuild targets
 	   --- 6.6 Commands useful for building a boot image
 	   --- 6.7 Custom kbuild commands
+	   --- 6.8 Preprocessing linker scripts
+	   --- 6.9 $(CC) support functions
 
 	=== 7 Kbuild Variables
 	=== 8 Makefile language
@@ -969,6 +971,59 @@ When kbuild executes the following steps are followed (roughly):
 	architecture specific files.
 
 
+--- 6.9 $(CC) support functions
+
+	The kernel may be build with several different versions of
+	$(CC), each supporting a unique set of features and options.
+	kbuild provide basic support to check for valid options for $(CC).
+	$(CC) is useally the gcc compiler, but other alternatives are
+	available.
+
+    cc-option
+	cc-option is used to check if $(CC) support a given option, and not
+	supported to use an optional second option.
+
+	Example:
+		#arch/i386/Makefile
+		cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
+
+	In the above example cflags-y will be assigned the option
+	-march=pentium-mmx if supported by $(CC), otherwise -march-i586.
+	The second argument to cc-option is optional, and if omitted
+	cflags-y will be assigned no value if first option is not supported.
+
+   cc-option-yn
+   	cc-option-yn is used to check if gcc supports a given option
+	and return 'y' if supported, otherwise 'n'.
+
+	Example:
+		#arch/ppc/Makefile
+		biarch := $(call cc-option-yn, -m32)
+		aflags-$(biarch) += -a32
+		cflags-$(biarch) += -m32
+	
+	In the above example $(biarch) is set to y if $(CC) supports the -m32
+	option. When $(biarch) equals to y the expanded variables $(aflags-y)
+	and $(cflags-y) will be assigned the values -a32 and -m32.
+
+    cc-version
+	cc-version return a numerical version of the $(CC) compiler version.
+	The format is <major><minor> where both are two digits. So for example
+	gcc 3.41 would return 0341.
+	cc-version is useful when a specific $(CC) version is faulty in one
+	area, for example the -mregparm=3 were broken in some gcc version
+	even though the option was accepted by gcc.
+
+	Example:
+		#arch/i386/Makefile
+		GCC_VERSION := $(call cc-version)
+		cflags-y += $(shell \
+		if [ $(GCC_VERSION) -ge 0300 ] ; then echo "-mregparm=3"; fi ;)
+
+	In the above example -mregparm=3 is only used for gcc version greater
+	than or equal to gcc 3.0.
+	
+
 === 7 Kbuild Variables
 
 The top Makefile exports the following variables:

Makefile

@@ -256,9 +256,32 @@ ifneq ($(findstring s,$(MAKEFLAGS)),)
   quiet=silent_
 endif
 
-check_gcc = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
+export quiet Q KBUILD_VERBOSE
+
+######
+# cc support functions to be used (only) in arch/$(ARCH)/Makefile
+# See documentation in Documentation/kbuild/makefiles.txt
+
+# cc-option
+# Usage: cflags-y += $(call gcc-option, -march=winchip-c6, -march=i586)
+
+cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+             > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
+
+# For backward compatibility
+check_gcc = $(warning check_gcc is deprecated - use cc-option) \
+            $(call cc-option, $(1),$(2))
+
+# cc-option-yn
+# Usage: flag := $(call gcc-option-yn, -march=winchip-c6)
+cc-option-yn = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+                > /dev/null 2>&1; then echo "y"; else echo "n"; fi;)
+
+# cc-version
+# Usage gcc-ver := $(call cc-version $(CC))
+cc-version = $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh \
+              $(if $(1), $(1), $(CC))
 
-export quiet Q KBUILD_VERBOSE check_gcc
 
 # Look for make include files relative to root of kernel src
 MAKEFLAGS += --include-dir=$(srctree)
@@ -463,7 +486,7 @@ CFLAGS		+= -g
 endif
 
 # warn about C99 declaration after statement
-CFLAGS += $(call check_gcc,-Wdeclaration-after-statement,)
+CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 
 #
 # INSTALL_PATH specifies where to place the updated kernel and system map

arch/i386/Makefile

@@ -23,43 +23,42 @@ CHECKFLAGS	+= -D__i386__=1
 CFLAGS += -pipe -msoft-float
 
 # prevent gcc from keeping the stack 16 byte aligned
-CFLAGS += $(call check_gcc,-mpreferred-stack-boundary=2,)
-
-align := $(subst -functions=0,,$(call check_gcc,-falign-functions=0,-malign-functions=0))
+CFLAGS += $(call cc-option,-mpreferred-stack-boundary=2)
 
+align := $(subst -functions=0,,$(call cc-option,-falign-functions=0,-malign-functions=0))
 cflags-$(CONFIG_M386)		+= -march=i386
 cflags-$(CONFIG_M486)		+= -march=i486
 cflags-$(CONFIG_M586)		+= -march=i586
 cflags-$(CONFIG_M586TSC)	+= -march=i586
-cflags-$(CONFIG_M586MMX)	+= $(call check_gcc,-march=pentium-mmx,-march=i586)
+cflags-$(CONFIG_M586MMX)	+= $(call cc-option,-march=pentium-mmx,-march=i586)
 cflags-$(CONFIG_M686)		+= -march=i686
-cflags-$(CONFIG_MPENTIUMII)	+= $(call check_gcc,-march=pentium2,-march=i686)
-cflags-$(CONFIG_MPENTIUMIII)	+= $(call check_gcc,-march=pentium3,-march=i686)
-cflags-$(CONFIG_MPENTIUMM)	+= $(call check_gcc,-march=pentium3,-march=i686)
-cflags-$(CONFIG_MPENTIUM4)	+= $(call check_gcc,-march=pentium4,-march=i686)
+cflags-$(CONFIG_MPENTIUMII)	+= $(call cc-option,-march=pentium2,-march=i686)
+cflags-$(CONFIG_MPENTIUMIII)	+= $(call cc-option,-march=pentium3,-march=i686)
+cflags-$(CONFIG_MPENTIUMM)	+= $(call cc-option,-march=pentium3,-march=i686)
+cflags-$(CONFIG_MPENTIUM4)	+= $(call cc-option,-march=pentium4,-march=i686)
 cflags-$(CONFIG_MK6)		+= -march=k6
 # Please note, that patches that add -march=athlon-xp and friends are pointless.
 # They make zero difference whatsosever to performance at this time.
-cflags-$(CONFIG_MK7)		+= $(call check_gcc,-march=athlon,-march=i686 $(align)-functions=4)
-cflags-$(CONFIG_MK8)		+= $(call check_gcc,-march=k8,$(call check_gcc,-march=athlon,-march=i686 $(align)-functions=4))
+cflags-$(CONFIG_MK7)		+= $(call cc-option,-march=athlon,-march=i686 $(align)-functions=4)
+cflags-$(CONFIG_MK8)		+= $(call cc-option,-march=k8,$(call cc-option,-march=athlon,-march=i686 $(align)-functions=4))
 cflags-$(CONFIG_MCRUSOE)	+= -march=i686 $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
-cflags-$(CONFIG_MWINCHIPC6)	+= $(call check_gcc,-march=winchip-c6,-march=i586)
-cflags-$(CONFIG_MWINCHIP2)	+= $(call check_gcc,-march=winchip2,-march=i586)
-cflags-$(CONFIG_MWINCHIP3D)	+= $(call check_gcc,-march=winchip2,-march=i586)
-cflags-$(CONFIG_MCYRIXIII)	+= $(call check_gcc,-march=c3,-march=i486) $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
-cflags-$(CONFIG_MVIAC3_2)	+= $(call check_gcc,-march=c3-2,-march=i686)
+cflags-$(CONFIG_MWINCHIPC6)	+= $(call cc-option,-march=winchip-c6,-march=i586)
+cflags-$(CONFIG_MWINCHIP2)	+= $(call cc-option,-march=winchip2,-march=i586)
+cflags-$(CONFIG_MWINCHIP3D)	+= $(call cc-option,-march=winchip2,-march=i586)
+cflags-$(CONFIG_MCYRIXIII)	+= $(call cc-option,-march=c3,-march=i486) $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
+cflags-$(CONFIG_MVIAC3_2)	+= $(call cc-option,-march=c3-2,-march=i686)
 
 # AMD Elan support
 cflags-$(CONFIG_X86_ELAN)	+= -march=i486
 
 # -mregparm=3 works ok on gcc-3.0 and later
 #
-GCC_VERSION			:= $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-version.sh $(CC))
+GCC_VERSION			:= $(call cc-version)
 cflags-$(CONFIG_REGPARM) 	+= $(shell if [ $(GCC_VERSION) -ge 0300 ] ; then echo "-mregparm=3"; fi ;)
 
 # Disable unit-at-a-time mode, it makes gcc use a lot more stack
 # due to the lack of sharing of stacklots.
-CFLAGS += $(call check_gcc,-fno-unit-at-a-time,)
+CFLAGS += $(call cc-option,-fno-unit-at-a-time)
 
 CFLAGS += $(cflags-y)