Date: Sun, 4 Nov 2007 12:16:40 +0100
From: Sam Ravnborg <sam@ravnborg.org>
To: David Miller <davem@davemloft.net>
Cc: mingo@elte.hu, bunk@kernel.org, thomas@archlinux.org, tglx@linutronix.de,
       linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
       akpm@linux-foundation.org
Subject: Re: 2.6.24-rc1-82798a1 compile failure (x86_64)
Message-ID: <20071104111640.GA17565@uranus.ravnborg.org>
References: <20071103121149.GA22149@uranus.ravnborg.org> <20071104020217.GJ12045@stusta.de> <20071104100429.GA12311@elte.hu> <20071104.023133.241080055.davem@davemloft.net>
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> I totally disagree.
> 
> People can't have it both ways.  CFLAGS has global meaning in every
> Makefile based build tree, it's not an "autoconf" thing.  This is well
> established practice, and I think it's a good thing the kernel does it
> now too.
> 
> If people set something like CFLAGS in their environment, they must
> understand what that means, and it means that universally it will
> influence your Makefile based builds.  Yes, this means all of them and
> even potentially the kernel build.
I'm afraid some people do not realize a whit about what they do.
So at least we could let kbuild warn about it.
Something like this:

$ export CFLAGS=-O3
$ make AFLAGS=-fisk
Makefile:540: "Appending $AFLAGS (-fisk) from command line to kernel defined $AFLAGS"
Makefile:544: "Appending $CFLAGS (-O3) from environment to kernel defined $CFLAGS"
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  CC      arch/x86/kernel/asm-offsets.s
  GEN     include/asm-x86/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  CC      scripts/mod/empty.o


This patch is needed to do so.

If one does a make O=... build then they will see the warning(s) twice.

	Sam

diff --git a/Makefile b/Makefile
index 188c3b6..1ae8779 100644
--- 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 "Appending $$$(1) ($($(1))) from $(origin $(1)) to kernel defined $$$(1)")
+
+ifneq ($(CPPFLAGS),)
+        $(call warn-assign,CPPFLAGS)
+        KBUILD_CPPFLAGS += $(CPPFLAGS)
+endif
+ifneq ($(AFLAGS),)
+        $(call warn-assign,AFLAGS)
+        KBUILD_AFLAGS += $(AFLAGS)
+endif
+ifneq ($(CFLAGS),)
+        $(call warn-assign,CFLAGS)
+        KBUILD_CFLAGS += $(CFLAGS)
+endif
 
 # Use --build-id when available.
 LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\
-
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