kbuild: enable 'make CFLAGS=...' to add additional options to CC

The variable CFLAGS is a wellknown variable and the usage by
kbuild may result in unexpected behaviour.
On top of that several people over time has asked for a way to
pass in additional flags to gcc.

This patch replace use of CFLAGS with KBUILD_CFLAGS all over the
tree and enabling one to use:
make CFLAGS=...
to specify additional gcc commandline options.

One usecase is when trying to find gcc bugs but other
use cases has been requested too.

Patch was tested on following architectures:
alpha, arm, i386, x86_64, mips, sparc, sparc64, ia64, m68k

Test was simple to do a defconfig build, apply the patch and check
that nothing got rebuild.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

arch/x86_64/Makefile

@@ -70,7 +70,7 @@ AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONF
 cflags-$(CONFIG_CC_STACKPROTECTOR) += $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh "$(CC)" -fstack-protector )
 cflags-$(CONFIG_CC_STACKPROTECTOR_ALL) += $(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh "$(CC)" -fstack-protector-all )
 
-CFLAGS += $(cflags-y)
+KBUILD_CFLAGS += $(cflags-y)
 CFLAGS_KERNEL += $(cflags-kernel-y)
 AFLAGS += -m64
 

arch/xtensa/Makefile

@@ -28,11 +28,9 @@ PLATFORM = $(platform-y)
 export PLATFORM
 
 # temporarily until string.h is fixed
-cflags-y += -ffreestanding
+KBUILD_CFLAGS += -ffreestanding
 
-cflags-y += -pipe -mlongcalls
-
-CFLAGS  += $(cflags-y)
+KBUILD_CFLAGS += -pipe -mlongcalls
 
 KBUILD_DEFCONFIG := iss_defconfig
 
@@ -56,7 +54,7 @@ endif
 
 #
 
-LIBGCC := $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
+LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
 
 head-y		:= arch/xtensa/kernel/head.o
 core-y		+= arch/xtensa/kernel/ arch/xtensa/mm/

arch/xtensa/boot/boot-redboot/Makefile

@@ -19,7 +19,7 @@ boot-y	:= bootstrap.o
 OBJS	:= $(addprefix $(obj)/,$(boot-y))
 LIBS	:= arch/xtensa/boot/lib/lib.a arch/xtensa/lib/lib.a
 
-LIBGCC := $(shell $(CC) $(CFLAGS) -print-libgcc-file-name)
+LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
 
 zImage: vmlinux $(OBJS) $(LIBS)
 	$(OBJCOPY) --strip-all -R .comment -R .xt.insn -O binary \

init/Makefile

@@ -30,4 +30,4 @@ $(obj)/version.o: include/linux/compile.h
 include/linux/compile.h: FORCE
 	@echo '  CHK     $@'
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@ \
-	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)" "$(CC) $(CFLAGS)"
+	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)" "$(CC) $(KBUILD_CFLAGS)"

scripts/Kbuild.include

@@ -75,7 +75,7 @@ try-run = $(shell set -e;		\
 # Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,)
 
 as-option = $(call try-run,\
-	$(CC) $(CFLAGS) $(1) -c -xassembler /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) $(KBUILD_CFLAGS) $(1) -c -xassembler /dev/null -o "$$TMP",$(1),$(2))
 
 # as-instr
 # Usage: cflags-y += $(call as-instr,instr,option1,option2)
@@ -87,12 +87,12 @@ as-instr = $(call try-run,\
 # Usage: cflags-y += $(call cc-option,-march=winchip-c6,-march=i586)
 
 cc-option = $(call try-run,\
-	$(CC) $(CFLAGS) $(1) -S -xc /dev/null -o "$$TMP",$(1),$(2))
+	$(CC) $(KBUILD_CFLAGS) $(1) -S -xc /dev/null -o "$$TMP",$(1),$(2))
 
 # cc-option-yn
 # Usage: flag := $(call cc-option-yn,-march=winchip-c6)
 cc-option-yn = $(call try-run,\
-	$(CC) $(CFLAGS) $(1) -S -xc /dev/null -o "$$TMP",y,n)
+	$(CC) $(KBUILD_CFLAGS) $(1) -S -xc /dev/null -o "$$TMP",y,n)
 
 # cc-option-align
 # Prefix align with either -falign or -malign

scripts/Makefile.lib

@@ -84,7 +84,7 @@ basename_flags = -D"KBUILD_BASENAME=KBUILD_STR($(call name-fix,$(basetarget)))"
 modname_flags  = $(if $(filter 1,$(words $(modname))),\
                  -D"KBUILD_MODNAME=KBUILD_STR($(call name-fix,$(modname)))")
 
-_c_flags       = $(CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(basetarget).o)
+_c_flags       = $(KBUILD_CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(basetarget).o)
 _a_flags       = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
 _cpp_flags     = $(CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))