[PATCH v4 12/22] objtool: Ignore jumps to the end of the function for checksum runs

[Josh Poimboeuf]

Sometimes Clang arm64 code jumps to the end of the function for UB.  No
need to make that an error for checksum runs, which are only run
manually by klp-build, and for which caring about UB is out of scope.

Such UBs are still reported for normal validate branch runs (for arches
which do that).

Signed-off-by: Josh Poimboeuf <jpoimboe at kernel.org>
---
 tools/objtool/check.c | 38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b353c7d6cd893..c034676e1b8c7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -38,6 +38,22 @@ struct disas_context *objtool_disas_ctx;
 
 size_t sym_name_max_len;
 
+static bool validate_branch_enabled(void)
+{
+	return opts.stackval	||
+	       opts.orc		||
+	       opts.uaccess;
+}
+
+static bool alts_needed(void)
+{
+	return validate_branch_enabled()	||
+	       opts.noinstr			||
+	       opts.hack_jump_label		||
+	       opts.disas			||
+	       opts.checksum;
+}
+
 struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset)
 {
@@ -1595,8 +1611,12 @@ static int add_jump_destinations(struct objtool_file *file)
 			/*
 			 * GCOV/KCOV dead code can jump to the end of
 			 * the function/section.
+			 *
+			 * Clang on arm64 also does this sometimes for
+			 * undefined behavior.
 			 */
-			if (file->ignore_unreachables && func &&
+			if ((!validate_branch_enabled() || file->ignore_unreachables) &&
+			    func &&
 			    dest_sec == insn->sec &&
 			    dest_off == func->offset + func->len)
 				continue;
@@ -2586,22 +2606,6 @@ static void mark_holes(struct objtool_file *file)
 	}
 }
 
-static bool validate_branch_enabled(void)
-{
-	return opts.stackval	||
-	       opts.orc		||
-	       opts.uaccess;
-}
-
-static bool alts_needed(void)
-{
-	return validate_branch_enabled()	||
-	       opts.noinstr			||
-	       opts.hack_jump_label		||
-	       opts.disas			||
-	       opts.checksum;
-}
-
 int decode_file(struct objtool_file *file)
 {
 	arch_initial_func_cfi_state(&initial_func_cfi);
-- 
2.54.0