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 <[email protected]>

Author: Sam Ravnborg

Documentation/kbuild/makefiles.txt

@@ -294,7 +294,7 @@ more details, with real examples.
 
 
 	This variable is necessary because the top Makefile owns the
-	variable $(CFLAGS) and uses it for compilation flags for the
+	variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
 	entire tree.
 
 	$(EXTRA_AFLAGS) is a similar string for per-directory options
@@ -437,6 +437,7 @@ more details, with real examples.
 	-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.
+	Note: cc-option uses KBUILD_CFLAGS for $(CC) options
 
    cc-option-yn
 	cc-option-yn is used to check if gcc supports a given option
@@ -452,6 +453,7 @@ more details, with real examples.
 	option. When $(biarch) equals 'y', the expanded variables $(aflags-y)
 	and $(cflags-y) will be assigned the values -a32 and -m32,
 	respectively.
+	Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
 
     cc-option-align
 	gcc versions >= 3.0 changed the type of options used to specify
@@ -463,10 +465,11 @@ more details, with real examples.
 		cc-option-align = -falign
 
 	Example:
-		CFLAGS += $(cc-option-align)-functions=4
+		KBUILD_CFLAGS += $(cc-option-align)-functions=4
 
 	In the above example, the option -falign-functions=4 is used for
 	gcc >= 3.00. For gcc < 3.00, -malign-functions=4 is used.
+	Note: cc-option-align uses KBUILD_CFLAGS for $(CC) options
 
     cc-version
 	cc-version returns a numerical version of the $(CC) compiler version.
@@ -825,17 +828,17 @@ When kbuild executes, the following steps are followed (roughly):
 		#arch/sparc64/Makefile
 		AFLAGS += -m64 -mcpu=ultrasparc
 
-    CFLAGS		$(CC) compiler flags
+    KBUILD_CFLAGS		$(CC) compiler flags
 
 	Default value - see top level Makefile
 	Append or modify as required per architecture.
 
-	Often, the CFLAGS variable depends on the configuration.
+	Often, the KBUILD_CFLAGS variable depends on the configuration.
 
 	Example:
 		#arch/i386/Makefile
 		cflags-$(CONFIG_M386) += -march=i386
-		CFLAGS += $(cflags-y)
+		KBUILD_CFLAGS += $(cflags-y)
 
 	Many arch Makefiles dynamically run the target C compiler to
 	probe supported options:
@@ -847,7 +850,7 @@ When kbuild executes, the following steps are followed (roughly):
 						-march=pentium2,-march=i686)
 		...
 		# Disable unit-at-a-time mode ...
-		CFLAGS += $(call cc-option,-fno-unit-at-a-time)
+		KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
 		...
 
 

Makefile

@@ -320,7 +320,7 @@ LINUXINCLUDE    := -Iinclude \
 
 CPPFLAGS        := -D__KERNEL__ $(LINUXINCLUDE)
 
-CFLAGS          := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
+KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
 		   -fno-strict-aliasing -fno-common \
 		   -Werror-implicit-function-declaration
 AFLAGS          := -D__ASSEMBLY__
@@ -335,7 +335,7 @@ 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 CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
+export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
 export AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 
 # When compiling out-of-tree modules, put MODVERDIR in the module
@@ -492,36 +492,36 @@ endif # $(dot-config)
 all: vmlinux
 
 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
-CFLAGS		+= -Os
+KBUILD_CFLAGS	+= -Os
 else
-CFLAGS		+= -O2
+KBUILD_CFLAGS	+= -O2
 endif
 
 include $(srctree)/arch/$(ARCH)/Makefile
 
 ifdef CONFIG_FRAME_POINTER
-CFLAGS		+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
+KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
 else
-CFLAGS		+= -fomit-frame-pointer
+KBUILD_CFLAGS	+= -fomit-frame-pointer
 endif
 
 ifdef CONFIG_DEBUG_INFO
-CFLAGS		+= -g
+KBUILD_CFLAGS	+= -g
 AFLAGS		+= -gdwarf-2
 endif
 
 # Force gcc to behave correct even for buggy distributions
-CFLAGS          += $(call cc-option, -fno-stack-protector)
+KBUILD_CFLAGS         += $(call cc-option, -fno-stack-protector)
 
 # arch Makefile may override CC so keep this after arch Makefile is included
 NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
 CHECKFLAGS     += $(NOSTDINC_FLAGS)
 
 # warn about C99 declaration after statement
-CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
+KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 
 # disable pointer signed / unsigned warnings in gcc 4.0
-CFLAGS += $(call cc-option,-Wno-pointer-sign,)
+KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
 
 # Use --build-id when available.
 LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\

arch/alpha/Makefile

@@ -84,7 +84,7 @@ endif
 # For TSUNAMI, we must have the assembler not emulate our instructions.
 # The same is true for IRONGATE, POLARIS, PYXIS.
 # BWX is most important, but we don't really want any emulation ever.
-CFLAGS += $(cflags-y) -Wa,-mev6
+KBUILD_CFLAGS += $(cflags-y) -Wa,-mev6
 
 head-y := arch/alpha/kernel/head.o
 

arch/alpha/kernel/Makefile

@@ -3,7 +3,7 @@
 #
 
 extra-y		:= head.o vmlinux.lds
-EXTRA_AFLAGS	:= $(CFLAGS)
+EXTRA_AFLAGS	:= $(KBUILD_CFLAGS)
 EXTRA_CFLAGS	:= -Werror -Wno-sign-compare
 
 obj-y    := entry.o traps.o process.o init_task.o osf_sys.o irq.o \

arch/alpha/lib/Makefile

@@ -2,7 +2,7 @@
 # Makefile for alpha-specific library files..
 #
 
-EXTRA_AFLAGS := $(CFLAGS)
+EXTRA_AFLAGS := $(KBUILD_CFLAGS)
 EXTRA_CFLAGS := -Werror
 
 # Many of these routines have implementations tuned for ev6.

arch/arm/Makefile

@@ -14,9 +14,9 @@ LDFLAGS_vmlinux	:=-p --no-undefined -X
 CPPFLAGS_vmlinux.lds = -DTEXT_OFFSET=$(TEXT_OFFSET)
 OBJCOPYFLAGS	:=-O binary -R .note -R .comment -S
 GZFLAGS		:=-9
-#CFLAGS		+=-pipe
+#KBUILD_CFLAGS	+=-pipe
 # Explicitly specifiy 32-bit ARM ISA since toolchain default can be -mthumb:
-CFLAGS		+=$(call cc-option,-marm,)
+KBUILD_CFLAGS	+=$(call cc-option,-marm,)
 
 # Do not use arch/arm/defconfig - it's always outdated.
 # Select a platform tht is kept up-to-date
@@ -28,7 +28,7 @@ MMUEXT		:= -nommu
 endif
 
 ifeq ($(CONFIG_FRAME_POINTER),y)
-CFLAGS		+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
+KBUILD_CFLAGS	+=-fno-omit-frame-pointer -mapcs -mno-sched-prolog
 endif
 
 ifeq ($(CONFIG_CPU_BIG_ENDIAN),y)
@@ -85,7 +85,7 @@ CFLAGS_ABI	:=$(call cc-option,-mapcs-32,-mabi=apcs-gnu) $(call cc-option,-mno-th
 endif
 
 # Need -Uarm for gcc < 3.x
-CFLAGS		+=$(CFLAGS_ABI) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
+KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
 AFLAGS		+=$(CFLAGS_ABI) $(arch-y) $(tune-y) -msoft-float
 
 CHECKFLAGS	+= -D__arm__

arch/arm/boot/compressed/Makefile

@@ -87,7 +87,7 @@ ifneq ($(PARAMS_PHYS),)
 LDFLAGS_vmlinux += --defsym params_phys=$(PARAMS_PHYS)
 endif
 LDFLAGS_vmlinux += -p --no-undefined -X \
-	$(shell $(CC) $(CFLAGS) --print-libgcc-file-name) -T
+	$(shell $(CC) $(KBUILD_CFLAGS) --print-libgcc-file-name) -T
 
 # Don't allow any static data in misc.o, which
 # would otherwise mess up our GOT table

arch/avr32/Makefile

@@ -11,14 +11,14 @@ all: uImage vmlinux.elf
 
 KBUILD_DEFCONFIG	:= atstk1002_defconfig
 
-CFLAGS		+= -pipe -fno-builtin -mno-pic
+KBUILD_CFLAGS	+= -pipe -fno-builtin -mno-pic
 AFLAGS		+= -mrelax -mno-pic
 CFLAGS_MODULE	+= -mno-relax
 LDFLAGS_vmlinux	+= --relax
 
 cpuflags-$(CONFIG_CPU_AT32AP7000)	+= -mcpu=ap7000
 
-CFLAGS		+= $(cpuflags-y)
+KBUILD_CFLAGS	+= $(cpuflags-y)
 AFLAGS		+= $(cpuflags-y)
 
 CHECKFLAGS	+= -D__avr32__ -D__BIG_ENDIAN

arch/blackfin/Makefile

@@ -53,7 +53,7 @@ rev-$(CONFIG_BF_REV_0_5)  := 0.5
 rev-$(CONFIG_BF_REV_NONE) := none
 rev-$(CONFIG_BF_REV_ANY)  := any
 
-CFLAGS += -mcpu=$(cpu-y)-$(rev-y)
+KBUILD_CFLAGS += -mcpu=$(cpu-y)-$(rev-y)
 AFLAGS += -mcpu=$(cpu-y)-$(rev-y)
 
 head-y   := arch/$(ARCH)/mach-$(MACHINE)/head.o arch/$(ARCH)/kernel/init_task.o

arch/cris/Makefile

@@ -31,16 +31,16 @@ OBJCOPYFLAGS := -O binary -R .note -R .comment -S
 CPPFLAGS_vmlinux.lds = -DDRAM_VIRTUAL_BASE=0x$(CONFIG_ETRAX_DRAM_VIRTUAL_BASE)
 AFLAGS += -mlinux
 
-CFLAGS := $(CFLAGS) -mlinux -march=$(arch-y) -pipe
+KBUILD_CFLAGS += -mlinux -march=$(arch-y) -pipe
 
 ifdef CONFIG_FRAME_POINTER
-CFLAGS := $(subst -fomit-frame-pointer,,$(CFLAGS)) -g
-CFLAGS += -fno-omit-frame-pointer
+KBUILD_CFLAGS := $(subst -fomit-frame-pointer,,$(KBUILD_CFLAGS)) -g
+KBUILD_CFLAGS += -fno-omit-frame-pointer
 endif
 
 head-y := arch/$(ARCH)/$(SARCH)/kernel/head.o
 
-LIBGCC = $(shell $(CC) $(CFLAGS) -print-file-name=libgcc.a)
+LIBGCC = $(shell $(CC) $(KBUILD_CFLAGS) -print-file-name=libgcc.a)
 
 core-y		+= arch/$(ARCH)/kernel/ arch/$(ARCH)/mm/
 core-y		+= arch/$(ARCH)/$(SARCH)/kernel/ arch/$(ARCH)/$(SARCH)/mm/

arch/frv/Makefile

@@ -39,39 +39,39 @@ endif
 ARCHMODFLAGS	+= -G0 -mlong-calls
 
 ifdef CONFIG_GPREL_DATA_8
-CFLAGS		+= -G8
+KBUILD_CFLAGS	+= -G8
 else
 ifdef CONFIG_GPREL_DATA_4
-CFLAGS		+= -G4
+KBUILD_CFLAGS	+= -G4
 else
 ifdef CONFIG_GPREL_DATA_NONE
-CFLAGS		+= -G0
+KBUILD_CFLAGS	+= -G0
 endif
 endif
 endif
 
 #LDFLAGS_vmlinux	:= -Map linkmap.txt
 
 ifdef CONFIG_GC_SECTIONS
-CFLAGS		+= -ffunction-sections -fdata-sections
+KBUILD_CFLAGS	+= -ffunction-sections -fdata-sections
 LINKFLAGS	+= --gc-sections
 endif
 
 ifndef CONFIG_FRAME_POINTER
-CFLAGS		+= -mno-linked-fp
+KBUILD_CFLAGS	+= -mno-linked-fp
 endif
 
 ifdef CONFIG_CPU_FR451_COMPILE
-CFLAGS		+= -mcpu=fr450
+KBUILD_CFLAGS	+= -mcpu=fr450
 AFLAGS		+= -mcpu=fr450
 ASFLAGS		+= -mcpu=fr450
 else
 ifdef CONFIG_CPU_FR551_COMPILE
-CFLAGS		+= -mcpu=fr550
+KBUILD_CFLAGS	+= -mcpu=fr550
 AFLAGS		+= -mcpu=fr550
 ASFLAGS		+= -mcpu=fr550
 else
-CFLAGS		+= -mcpu=fr400
+KBUILD_CFLAGS	+= -mcpu=fr400
 AFLAGS		+= -mcpu=fr400
 ASFLAGS		+= -mcpu=fr400
 endif
@@ -80,15 +80,15 @@ endif
 # pretend the kernel is going to run on an FR400 with no media-fp unit
 # - reserve CC3 for use with atomic ops
 # - all the extra registers are dealt with only at context switch time
-CFLAGS		+= -mno-fdpic -mgpr-32 -msoft-float -mno-media
-CFLAGS		+= -ffixed-fcc3 -ffixed-cc3 -ffixed-gr15 -ffixed-icc2
+KBUILD_CFLAGS	+= -mno-fdpic -mgpr-32 -msoft-float -mno-media
+KBUILD_CFLAGS	+= -ffixed-fcc3 -ffixed-cc3 -ffixed-gr15 -ffixed-icc2
 AFLAGS		+= -mno-fdpic
 ASFLAGS		+= -mno-fdpic
 
 # make sure the .S files get compiled with debug info
 # and disable optimisations that are unhelpful whilst debugging
 ifdef CONFIG_DEBUG_INFO
-#CFLAGS		+= -O1
+#KBUILD_CFLAGS	+= -O1
 AFLAGS		+= -Wa,--gdwarf2
 ASFLAGS		+= -Wa,--gdwarf2
 endif

arch/h8300/Makefile

@@ -30,16 +30,16 @@ ldflags-$(CONFIG_CPU_H8300H)	:= -mh8300helf
 cflags-$(CONFIG_CPU_H8S)	:= -ms
 ldflags-$(CONFIG_CPU_H8S)	:= -mh8300self
 
-CFLAGS += $(cflags-y)
-CFLAGS += -mint32 -fno-builtin
-CFLAGS += -g
-CFLAGS += -D__linux__
-CFLAGS += -DUTS_SYSNAME=\"uClinux\"
+KBUILD_CFLAGS += $(cflags-y)
+KBUILD_CFLAGS += -mint32 -fno-builtin
+KBUILD_CFLAGS += -g
+KBUILD_CFLAGS += -D__linux__
+KBUILD_CFLAGS += -DUTS_SYSNAME=\"uClinux\"
 AFLAGS += -DPLATFORM=$(PLATFORM) -DMODEL=$(MODEL) $(cflags-y)
 LDFLAGS += $(ldflags-y)
 
 CROSS_COMPILE = h8300-elf-
-LIBGCC := $(shell $(CROSS-COMPILE)$(CC) $(CFLAGS) -print-libgcc-file-name)
+LIBGCC := $(shell $(CROSS-COMPILE)$(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
 
 head-y := arch/$(ARCH)/platform/$(PLATFORM)/$(BOARD)/crt0_$(MODEL).o
 

arch/i386/Makefile

@@ -34,10 +34,10 @@ LDFLAGS_vmlinux := --emit-relocs
 endif
 CHECKFLAGS	+= -D__i386__
 
-CFLAGS += -pipe -msoft-float -mregparm=3 -freg-struct-return
+KBUILD_CFLAGS += -pipe -msoft-float -mregparm=3 -freg-struct-return
 
 # prevent gcc from keeping the stack 16 byte aligned
-CFLAGS += $(call cc-option,-mpreferred-stack-boundary=2)
+KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=2)
 
 # CPU-specific tuning. Anything which can be shared with UML should go here.
 include $(srctree)/arch/i386/Makefile.cpu
@@ -51,7 +51,7 @@ cflags-y += -maccumulate-outgoing-args
 
 # Disable unit-at-a-time mode on pre-gcc-4.0 compilers, it makes gcc use
 # a lot more stack due to the lack of sharing of stacklots:
-CFLAGS				+= $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)
+KBUILD_CFLAGS += $(shell if [ $(call cc-version) -lt 0400 ] ; then echo $(call cc-option,-fno-unit-at-a-time); fi ;)
 
 # do binutils support CFI?
 cflags-y += $(call as-instr,.cfi_startproc\n.cfi_rel_offset esp${comma}0\n.cfi_endproc,-DCONFIG_AS_CFI=1,)
@@ -61,7 +61,7 @@ AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_rel_offset esp${comma}0\n.cfi_end
 cflags-y += $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1,)
 AFLAGS += $(call as-instr,.cfi_startproc\n.cfi_signal_frame\n.cfi_endproc,-DCONFIG_AS_CFI_SIGNAL_FRAME=1,)
 
-CFLAGS += $(cflags-y)
+KBUILD_CFLAGS += $(cflags-y)
 
 # Default subarch .c files
 mcore-y  := arch/x86/mach-default
@@ -116,7 +116,7 @@ drivers-$(CONFIG_OPROFILE)		+= arch/x86/oprofile/
 drivers-$(CONFIG_PM)			+= arch/x86/power/
 drivers-$(CONFIG_FB)                    += arch/x86/video/
 
-CFLAGS += $(mflags-y)
+KBUILD_CFLAGS += $(mflags-y)
 AFLAGS += $(mflags-y)
 
 boot := arch/x86/boot

arch/ia64/Makefile

@@ -44,7 +44,7 @@ ifeq ($(call cc-version),0304)
 	cflags-$(CONFIG_MCKINLEY)	+= -mtune=mckinley
 endif
 
-CFLAGS += $(cflags-y)
+KBUILD_CFLAGS += $(cflags-y)
 head-y := arch/ia64/kernel/head.o arch/ia64/kernel/init_task.o
 
 libs-y				+= arch/ia64/lib/