objtool: Clobber user CFLAGS variable

If the build user has the CFLAGS variable set in their environment,
objtool blindly appends to it, which can cause unexpected behavior.

Clobber CFLAGS to ensure consistent objtool compilation behavior.

Reported-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Tested-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/83a276df209962e6058fcb6c615eef9d401c21bc.1567121311.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 8815823..20f67fc 100644 (file)
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -35,7 +35,7 @@ INCLUDES := -I$(srctree)/tools/include \
            -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi \
            -I$(srctree)/tools/objtool/arch/$(ARCH)/include
 WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed
-CFLAGS   += -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
+CFLAGS   := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
 LDFLAGS  += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
 
 # Allow old libelf to be used: