linux-kernel - Re: next-20190826 - objtool fails to build.

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Date:   Wed, 28 Aug 2019 14:51:00 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Valdis Klētnieks <valdis.kletnieks@...edu>
Cc:     Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: next-20190826 - objtool fails to build.

On Wed, Aug 28, 2019 at 03:30:00PM -0400, Valdis Klētnieks wrote:
> On Wed, 28 Aug 2019 10:10:04 -0500, Josh Poimboeuf said:
> 
> > But I don't see how those warnings could get enabled: -Wsign-compare
> > -Wunused-parameter.
> >
> > Can you "make clean" and do "make V=1 tools/objtool" to show the actual
> > flags?
> 
> And that tells me those warnings in fact don't get specifically enabled.
> (I've added some line breaks for sanity)
> 
>   gcc -Wp,-MD,/usr/src/linux-next/tools/objtool/.special.o.d -Wp,-MT,/usr/src/linux-next/tools/objtool/special.o -O2 -D_FORTIFY_SOURCE=2 -Wall -Wextra -Wbad-function-cast
> 
> Found the cause of the mystery - I changed something in a bash profile, and
> as a result...
> 
> export CFLAGS="-O2 -D_FORTIFY_SOURCE=2 -Wall -Wextra"
> 
> And -Wextra pulls in the things that cause problems. So this is mostly
> self-inflicted.
> 
> The real question then becomes - should the Makefile sanitize CFLAGS or just
> append to whatever the user supplied as it does currently? The rest of the tree
> sanitizes CFLAG, because I don't get deluged in -Wsign-compare warnings all
> over the place...

Agreed.  I assume this fixes it?

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 88158239622b..20f67fcf378d 100644
--- 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)
 
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