kbuild: enable 'make CPPFLAGS=...' to add additional options to CPP

The variable CPPFLAGS is a wellknown variable and the usage by
kbuild may result in unexpected behaviour.

This patch replace use of CPPFLAGS with KBUILD_CPPFLAGS all over the
tree and enabling one to use:
make CPPFLAGS=...
to specify additional CPP commandline options.

Patch was tested on following architectures:
alpha, arm, i386, x86_64, mips, sparc, sparc64, ia64, m68k, s390
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Documentation/kbuild/makefiles.txt

@@ -1099,7 +1099,7 @@ When kbuild executes, the following steps are followed (roughly):
 	specified options when building the target vmlinux.lds.
 
 	When building the *.lds target, kbuild uses the variables:
-	CPPFLAGS	: Set in top-level Makefile
+	KBUILD_CPPFLAGS	: Set in top-level Makefile
 	EXTRA_CPPFLAGS	: May be set in the kbuild makefile
 	CPPFLAGS_$(@F)  : Target specific flags.
 	                  Note that the full filename is used in this

Makefile

@@ -318,7 +318,7 @@ LINUXINCLUDE    := -Iinclude \
                    $(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include) \
 		   -include include/linux/autoconf.h
 
-CPPFLAGS        := -D__KERNEL__ $(LINUXINCLUDE)
+KBUILD_CPPFLAGS := -D__KERNEL__ $(LINUXINCLUDE)
 
 KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		   -fno-strict-aliasing -fno-common \
@@ -334,7 +334,7 @@ export ARCH SRCARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE
 export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
-export CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
+export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
 export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
 export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 
@@ -523,7 +523,8 @@ KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 # disable pointer signed / unsigned warnings in gcc 4.0
 KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
 
-# Add user supplied AFLAGS and CFLAGS as the last assignments
+# Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
+KBUILD_CPPFLAGS += $(CPPFLAGS)
 KBUILD_AFLAGS   += $(AFLAGS)
 KBUILD_CFLAGS   += $(CFLAGS)
 
@@ -1507,7 +1508,7 @@ quiet_cmd_rmfiles = $(if $(wildcard $(rm-files)),CLEAN   $(wildcard $(rm-files))
 
 
 a_flags = -Wp,-MD,$(depfile) $(KBUILD_AFLAGS) $(AFLAGS_KERNEL) \
-	  $(NOSTDINC_FLAGS) $(CPPFLAGS) \
+	  $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
 	  $(modkern_aflags) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
 
 quiet_cmd_as_o_S = AS      $@

arch/arm/Makefile

@@ -32,11 +32,11 @@ KBUILD_CFLAGS	+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
 endif
 
 ifeq ($(CONFIG_CPU_BIG_ENDIAN),y)
-CPPFLAGS	+= -mbig-endian
+KBUILD_CPPFLAGS	+= -mbig-endian
 AS		+= -EB
 LD		+= -EB
 else
-CPPFLAGS	+= -mlittle-endian
+KBUILD_CPPFLAGS	+= -mlittle-endian
 AS		+= -EL
 LD		+= -EL
 endif

arch/ia64/Makefile

@@ -29,7 +29,7 @@ cflags-y	:= -pipe $(EXTRA) -ffixed-r13 -mfixed-range=f12-f15,f32-f127 \
 CFLAGS_KERNEL	:= -mconstant-gp
 
 GAS_STATUS	= $(shell $(srctree)/arch/ia64/scripts/check-gas "$(CC)" "$(OBJDUMP)")
-CPPFLAGS += $(shell $(srctree)/arch/ia64/scripts/toolchain-flags "$(CC)" "$(OBJDUMP)" "$(READELF)")
+KBUILD_CPPFLAGS += $(shell $(srctree)/arch/ia64/scripts/toolchain-flags "$(CC)" "$(OBJDUMP)" "$(READELF)")
 
 ifeq ($(GAS_STATUS),buggy)
 $(error Sorry, you need a newer version of the assember, one that is built from	\

arch/powerpc/Makefile

@@ -75,7 +75,7 @@ CPPFLAGS-$(CONFIG_PPC32) := -Iarch/$(ARCH)
 AFLAGS-$(CONFIG_PPC32)	:= -Iarch/$(ARCH)
 CFLAGS-$(CONFIG_PPC64)	:= -mminimal-toc -mtraceback=none  -mcall-aixdesc
 CFLAGS-$(CONFIG_PPC32)	:= -Iarch/$(ARCH) -ffixed-r2 -mmultiple
-CPPFLAGS	+= $(CPPFLAGS-y)
+KBUILD_CPPFLAGS	+= $(CPPFLAGS-y)
 KBUILD_AFLAGS	+= $(AFLAGS-y)
 KBUILD_CFLAGS	+= -msoft-float -pipe $(CFLAGS-y)
 CPP		= $(CC) -E $(KBUILD_CFLAGS)

arch/ppc/Makefile

@@ -22,7 +22,7 @@ endif
 
 LDFLAGS_vmlinux	:= -Ttext $(KERNELLOAD) -Bstatic
 # The -Iarch/$(ARCH)/include is temporary while we are merging
-CPPFLAGS	+= -Iarch/$(ARCH) -Iarch/$(ARCH)/include
+KBUILD_CPPFLAGS	+= -Iarch/$(ARCH) -Iarch/$(ARCH)/include
 KBUILD_AFLAGS	+= -Iarch/$(ARCH)
 KBUILD_CFLAGS	+= -Iarch/$(ARCH) -msoft-float -pipe \
 		-ffixed-r2 -mmultiple

arch/um/Makefile-x86_64

@@ -14,7 +14,7 @@ KBUILD_CFLAGS += $(_extra_flags_)
 CHECKFLAGS  += -m64
 KBUILD_AFLAGS += -m64
 LDFLAGS += -m elf_x86_64
-CPPFLAGS += -m64
+KBUILD_CPPFLAGS += -m64
 
 ELF_ARCH := i386:x86-64
 ELF_FORMAT := elf64-x86-64

drivers/atm/Makefile

@@ -41,7 +41,7 @@ ifeq ($(CONFIG_ATM_FORE200E_PCA),y)
   # guess the target endianess to choose the right PCA-200E firmware image
   ifeq ($(CONFIG_ATM_FORE200E_PCA_DEFAULT_FW),y)
     byteorder.h			:= include$(if $(patsubst $(srctree),,$(objtree)),2)/asm/byteorder.h
-    CONFIG_ATM_FORE200E_PCA_FW	:= $(obj)/pca200e$(if $(shell $(CC) $(CPPFLAGS) -E -dM $(byteorder.h) | grep ' __LITTLE_ENDIAN '),.bin,_ecd.bin2)
+    CONFIG_ATM_FORE200E_PCA_FW	:= $(obj)/pca200e$(if $(shell $(CC) $(KBUILD_CPPFLAGS) -E -dM $(byteorder.h) | grep ' __LITTLE_ENDIAN '),.bin,_ecd.bin2)
   endif
 endif
 

scripts/Makefile.lib

@@ -86,7 +86,7 @@ modname_flags  = $(if $(filter 1,$(words $(modname))),\
 
 _c_flags       = $(KBUILD_CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(basetarget).o)
 _a_flags       = $(KBUILD_AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(basetarget).o)
-_cpp_flags     = $(CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))
+_cpp_flags     = $(KBUILD_CPPFLAGS) $(EXTRA_CPPFLAGS) $(CPPFLAGS_$(@F))
 
 # If building the kernel in a separate objtree expand all occurrences
 # of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
@@ -106,11 +106,11 @@ __a_flags	=                          $(call flags,_a_flags)
 __cpp_flags     =                          $(call flags,_cpp_flags)
 endif
 
-c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
+c_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
 		 $(__c_flags) $(modkern_cflags) \
 		 -D"KBUILD_STR(s)=\#s" $(basename_flags) $(modname_flags)
 
-a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \
+a_flags        = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(KBUILD_CPPFLAGS) \
 		 $(__a_flags) $(modkern_aflags)
 
 cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)