linux-kernel - [PATCH] objtool: allow building with older libelf

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Date:	Fri, 13 May 2016 00:21:42 -0600
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Josh Poimboeuf" <jpoimboe@...hat.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] objtool: allow building with older libelf

The switch to elf_getshdr{num,strndx} post-dates the oldest tool chain
the kernel is supposed to be able to build with, so try to cope with
such an environment.

Signed-off-by: Jan Beulich <jbeulich@...e.com>
---
 tools/objtool/Makefile        |    4 ++++
 tools/objtool/elf.h           |    5 +++++
 2 files changed, 9 insertions(+)

--- 4.6-rc7/tools/objtool/Makefile
+++ 4.6-rc7-objtool-older-libelf/tools/objtool/Makefile
@@ -30,6 +30,10 @@ INCLUDES := -I$(srctree)/tools/include
 CFLAGS   += -Wall -Werror $(EXTRA_WARNINGS) -fomit-frame-pointer -O2 -g $(INCLUDES)
 LDFLAGS  += -lelf $(LIBSUBCMD)
 
+# Allow old libelf to be used:
+elfshdr := $(shell echo '\#include <libelf.h>' | $(CC) $(CFLAGS) -x c -E - | grep elf_getshdr)
+CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
+
 AWK = awk
 export srctree OUTPUT CFLAGS ARCH AWK
 include $(srctree)/tools/build/Makefile.include
--- 4.6-rc7/tools/objtool/elf.h
+++ 4.6-rc7-objtool-older-libelf/tools/objtool/elf.h
@@ -23,6 +23,11 @@
 #include <linux/list.h>
 #include <linux/hashtable.h>
 
+#ifdef LIBELF_USE_DEPRECATED
+# define elf_getshdrnum    elf_getshnum
+# define elf_getshdrstrndx elf_getshstrndx
+#endif
+
 struct section {
 	struct list_head list;
 	GElf_Shdr sh;