objtool: Ignore empty alternatives

The .alternatives section can contain entries with no original
instructions. Objtool will currently crash when handling such an entry.

Just skip that entry, but still give a warning to discourage useless
entries.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5b67d6150a0b1cdfab577b893325b2fde7ff4dd9..efb9640135527c493bab7049340852fb879d0dd2 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -905,6 +905,12 @@ static int add_special_section_alts(struct objtool_file *file)
                }
 
                if (special_alt->group) {
+                       if (!special_alt->orig_len) {
+                               WARN_FUNC("empty alternative entry",
+                                         orig_insn->sec, orig_insn->offset);
+                               continue;
+                       }
+
                        ret = handle_group_alt(file, special_alt, orig_insn,
                                               &new_insn);
                        if (ret)