objtool: Use '.strtab' if '.shstrtab' doesn't exist, to support ORC tables on Clang

Clang puts its section header names in the '.strtab' section instead of
'.shstrtab', which causes objtool to fail with a "can't find
.shstrtab section" warning when attempting to write ORC metadata to an
object file.

If '.shstrtab' doesn't exist, use '.strtab' instead.

Signed-off-by: Simon Ser <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/d1c1c3fe55872be433da7bc5e1860538506229ba.1531153015.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 0d1acb7..7ec85d5 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -519,10 +519,12 @@ struct section *elf_create_section(struct elf *elf, const char *name,
 	sec->sh.sh_flags = SHF_ALLOC;
 
 
-	/* Add section name to .shstrtab */
+	/* Add section name to .shstrtab (or .strtab for Clang) */
 	shstrtab = find_section_by_name(elf, ".shstrtab");
+	if (!shstrtab)
+		shstrtab = find_section_by_name(elf, ".strtab");
 	if (!shstrtab) {
-		WARN("can't find .shstrtab section");
+		WARN("can't find .shstrtab or .strtab section");
 		return NULL;
 	}