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

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Message-Id: <732dae6872b7ff187d94f22bb699a12849d3fe04.1463430618.git.jpoimboe@redhat.com>
Date:	Mon, 16 May 2016 15:31:07 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Jan Beulich <JBeulich@...e.com>
Subject: [PATCH] objtool: allow building with older libelf

From: Jan Beulich <JBeulich@...e.com>

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>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/Makefile | 4 ++++
 tools/objtool/elf.h    | 5 +++++
 2 files changed, 9 insertions(+)

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index 6765c7e..f094f3c 100644
--- a/tools/objtool/Makefile
+++ b/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
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index 7f3e00a..aa1ff65 100644
--- a/tools/objtool/elf.h
+++ b/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;
-- 
2.4.11