kbuild: introduce subdir-ccflags-y

Following patch introduce support for setting options
to gcc that has effect for current directory and all
subdirectories.

The typical use case are an architecture or a subsystem that
decide to cover all files with -Werror.
Today alpha, mips and sparc uses -Werror in almost all their
Makefile- with subdir-ccflag-y it is now simpler to do so
as only the top-level directories needs to be covered.

Likewise if we decide to cover a full subsystem such
as net/ with -Werror this is done by adding a single
line to net/Makefile.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>

Documentation/kbuild/makefiles.txt

@@ -316,6 +316,16 @@ more details, with real examples.
 		#arch/m68k/fpsp040/Makefile
 		ldflags-y := -x
 
+    subdir-ccflags-y, subdir-asflags-y
+	The two flags listed above are similar to ccflags-y and as-falgs-y.
+	The difference is that the subdir- variants has effect for the kbuild
+	file where tey are present and all subdirectories.
+	Options specified using subdir-* are added to the commandline before
+	the options specified using the non-subdir variants.
+
+	Example:
+		subdir-ccflags-y := -Werror
+
     CFLAGS_$@, AFLAGS_$@
 
 	CFLAGS_$@ and AFLAGS_$@ only apply to commands in current

scripts/Makefile.build

@@ -27,6 +27,9 @@ ccflags-y  :=
 cppflags-y :=
 ldflags-y  :=
 
+subdir-asflags-y :=
+subdir-ccflags-y :=
+
 # Read auto.conf if it exists, otherwise ignore
 -include include/config/auto.conf
 

scripts/Makefile.lib

@@ -4,6 +4,11 @@ ccflags-y  += $(EXTRA_CFLAGS)
 cppflags-y += $(EXTRA_CPPFLAGS)
 ldflags-y  += $(EXTRA_LDFLAGS)
 
+#
+# flags that take effect in sub directories
+export KBUILD_SUBDIR_ASFLAGS := $(KBUILD_SUBDIR_ASFLAGS) $(subdir-asflags-y)
+export KBUILD_SUBDIR_CCFLAGS := $(KBUILD_SUBDIR_CCFLAGS) $(subdir-ccflags-y)
+
 # Figure out what we need to build from the various variables
 # ===========================================================================
 
@@ -104,10 +109,10 @@ else
 debug_flags =
 endif
 
-orig_c_flags   = $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS)                     \
+orig_c_flags   = $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(KBUILD_SUBDIR_CCFLAGS) \
                  $(ccflags-y) $(CFLAGS_$(basetarget).o)
 _c_flags       = $(filter-out $(CFLAGS_REMOVE_$(basetarget).o), $(orig_c_flags))
-_a_flags       = $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS)                     \
+_a_flags       = $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS) $(KBUILD_SUBDIR_ASFLAGS) \
                  $(asflags-y) $(AFLAGS_$(basetarget).o)
 _cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(@F))