linux-kernel - [PATCH 4.9 056/128] objtool: Ignore empty alternatives

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Message-Id: <20200619141623.160513124@linuxfoundation.org>
Date:   Fri, 19 Jun 2020 16:32:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Julien Thierry <jthierry@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 056/128] objtool: Ignore empty alternatives

From: Julien Thierry <jthierry@...hat.com>

[ Upstream commit 7170cf47d16f1ba29eca07fd818870b7af0a93a5 ]

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@...hat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/objtool/check.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b0b8ba9b800c..c7399d7f4bc7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -778,6 +778,12 @@ 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)
-- 
2.25.1