[RFC PATCH v3 12/13] objtool: arm64: Ignore replacement section for alternative callback

[Chen Zhongjin <chenzhongjin@huawei.com>]

From: Julien Thierry <jthierry@redhat.com>

ARM64_CB_PATCH doesn't have static replacement instructions. Skip
trying to validate the alternative section.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
---
 tools/objtool/arch/arm64/special.c | 11 +++++++++++
 tools/objtool/check.c              |  3 +++
 2 files changed, 14 insertions(+)

diff --git a/tools/objtool/arch/arm64/special.c b/tools/objtool/arch/arm64/special.c
index a70b91e8bd7d..8bb1ebd2132a 100644
--- a/tools/objtool/arch/arm64/special.c
+++ b/tools/objtool/arch/arm64/special.c
@@ -4,6 +4,17 @@
 
 void arch_handle_alternative(unsigned short feature, struct special_alt *alt)
 {
+	/*
+	 * ARM64_CB_PATCH has no alternative instruction.
+	 * a callback is called at alternative replacement time
+	 * to dynamically change the original instructions.
+	 *
+	 * ARM64_CB_PATCH is the last ARM64 feature, it's value changes
+	 * every time a new feature is added. So the orig/alt region
+	 * length are used to detect those alternatives
+	 */
+	if (alt->orig_len && !alt->new_len)
+		alt->skip_alt = true;
 }
 
 bool arch_support_alt_relocation(struct special_alt *special_alt,
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b2135da41f48..596974030382 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1647,6 +1647,9 @@ static int add_special_section_alts(struct objtool_file *file)
 				continue;
 			}
 
+			if (special_alt->skip_alt && !special_alt->new_len)
+				continue;
+
 			ret = handle_group_alt(file, special_alt, orig_insn,
 					       &new_insn);
 			if (ret)
-- 
2.17.1