linux-kernel - Re: [PATCH] objtool: query pkg-config for libelf location

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Date:   Wed, 20 Mar 2019 10:37:01 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Rolf Eike Beer <eb@...ix.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] objtool: query pkg-config for libelf location

On Tue, Mar 19, 2019 at 08:20:12AM +0100, Rolf Eike Beer wrote:
> If it is not in the default location compilation would fail at several points.
> 
> Signed-off-by: Rolf Eike Beer <eb@...ix.com>
> ---
>  Makefile               | 4 +++-
>  tools/objtool/Makefile | 7 +++++--
>  2 files changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index 9ef547fc7ffe..666b52c1c5f4 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -940,9 +940,11 @@ mod_sign_cmd = true
>  endif
>  export mod_sign_cmd
>  
> +HOST_LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)
> +
>  ifdef CONFIG_STACK_VALIDATION
>    has_libelf := $(call try-run,\
> -		echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
> +		echo "int main() {}" | $(HOSTCC) -xc -o /dev/null $(HOST_LIBELF_LIBS) -,1,0)
>    ifeq ($(has_libelf),1)
>      objtool_target := tools/objtool FORCE
>    else
> diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
> index c9d038f91af6..0c8dd1609348 100644
> --- a/tools/objtool/Makefile
> +++ b/tools/objtool/Makefile
> @@ -25,14 +25,17 @@ LIBSUBCMD		= $(LIBSUBCMD_OUTPUT)libsubcmd.a
>  OBJTOOL    := $(OUTPUT)objtool
>  OBJTOOL_IN := $(OBJTOOL)-in.o
>  
> +LIBELF_FLAGS = $(shell pkg-config libelf --cflags)
> +LIBELF_LIBS = $(shell pkg-config libelf --libs 2>/dev/null || echo -lelf)

Should LIBELF_FLAGS also pipe stderr to /dev/null?

> +
>  all: $(OBJTOOL)
>  
>  INCLUDES := -I$(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)
> -LDFLAGS  += -lelf $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
> +CFLAGS   += -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
> +LDFLAGS  += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
>  
>  # Allow old libelf to be used:
>  elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
> -- 
> 2.21.0
> 
> 
> -- 
> Rolf Eike Beer, emlix GmbH, http://www.emlix.com
> Fon +49 551 30664-0, Fax +49 551 30664-11
> Gothaer Platz 3, 37083 Göttingen, Germany
> Sitz der Gesellschaft: Göttingen, Amtsgericht Göttingen HR B 3160
> Geschäftsführung: Heike Jordan, Dr. Uwe Kracke – Ust-IdNr.: DE 205 198 055
> 
> emlix - smart embedded open source
> 
> 
> 

-- 
Josh