[PATCH] objtool: Be lenient about -Wundef

[Olof Johansson]

Some libelf versions use undefined macros, which combined with newer GCC
makes for errors from system headers. This isn't overly useful to fail
compiling objtool for.

Error as seen:

cc1: all warnings being treated as errors
In file included from arch/x86/../../elf.h:10,
                 from arch/x86/decode.c:14:
/usr/include/libelf/gelf.h:25:5: error: "__LIBELF_INTERNAL__" is not defined, evaluates to 0 [-Werror=undef]
 #if __LIBELF_INTERNAL__
     ^~~~~~~~~~~~~~~~~~~

For this reason, skip -Wundef on objtool.

Signed-off-by: Olof Johansson <olof@xxxxxxxxx>
---
 tools/objtool/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 88158239622bc..0c49206c5216b 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -35,6 +35,8 @@ 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
+# Some system libelf versions uses undefined "#if <var>", so skip the warning/error
+WARNINGS += -Wno-undef
 CFLAGS   += -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS)
 LDFLAGS  += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS)
 
-- 
2.11.0