kbuild: do not pick up CFLAGS from the environment

Too many people have CFLAGS set to support building userspace.
And now Kbuild picks up CFLAGS this caused troubles.

Although people should realise that setting CFLAGS has
a 'global' effect the impact on the kernel build is a suprise.
So change kbuild to pick up value from KCFLAGS that is
much less used.

When kbuild pick up a value it will warn like this:
Makefile:544: "WARNING: Appending $KCFLAGS (-O3) from environment to kernel $CFLAGS"

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Bächler <thomas@archlinux.org>
Cc: David Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@redhat.com>

diff --git a/Makefile b/Makefile
index 188c3b6b3fa9ac33fbe9fba2417365eae23585d6..cb740d4d4e8cb89f67d7a542fbe804e6afe1b604 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -528,9 +528,22 @@ KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 KBUILD_CFLAGS += $(call cc-option,-Wno-pointer-sign,)
 
 # Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
-KBUILD_CPPFLAGS += $(CPPFLAGS)
-KBUILD_AFLAGS   += $(AFLAGS)
-KBUILD_CFLAGS   += $(CFLAGS)
+# But warn user when we do so
+warn-assign = \
+$(warning "WARNING: Appending $$K$(1) ($(K$(1))) from $(origin K$(1)) to kernel $$$(1)")
+
+ifneq ($(KCPPFLAGS),)
+        $(call warn-assign,CPPFLAGS)
+        KBUILD_CPPFLAGS += $(KCPPFLAGS)
+endif
+ifneq ($(KAFLAGS),)
+        $(call warn-assign,AFLAGS)
+        KBUILD_AFLAGS += $(KAFLAGS)
+endif
+ifneq ($(KCFLAGS),)
+        $(call warn-assign,CFLAGS)
+        KBUILD_CFLAGS += $(KCFLAGS)
+endif
 
 # Use --build-id when available.
 LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\