[tip: objtool/core] objtool: Ignore empty alternatives

[tip-bot2 for Julien Thierry]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     4801206d6c21fb21cdb50712a903f079f7597219
Gitweb:        https://git.kernel.org/tip/4801206d6c21fb21cdb50712a903f079f7597219
Author:        Julien Thierry <jthierry@xxxxxxxxxx>
AuthorDate:    Fri, 27 Mar 2020 15:28:41 
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Tue, 14 Apr 2020 10:39:25 -05:00

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@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/check.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 93ef14a..34b3d7b 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -923,6 +923,12 @@ 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)