objtool: Fix seg fault with clang-compiled objects

Fix a seg fault which happens when an input file provided to 'objtool
orc generate' doesn't have a '.shstrtab' section (for instance, object
files produced by clang don't have this section).

Signed-off-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/c0f2231683e9bed40fac1f13ce2c33b8389854bc.1514666459.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/objtool/orc_gen.c

@@ -165,6 +165,8 @@ int create_orc_sections(struct objtool_file *file)
 
 	/* create .orc_unwind_ip and .rela.orc_unwind_ip sections */
 	sec = elf_create_section(file->elf, ".orc_unwind_ip", sizeof(int), idx);
+	if (!sec)
+		return -1;
 
 	ip_relasec = elf_create_rela_section(file->elf, sec);
 	if (!ip_relasec)