Objtool doesn't consider a jump to be a sibling call if the destination
isn't a function, so srso_alias_untrain_ret()'s jump to
srso_alias_return_thunk() is ignored by objtool and the former is
falsely classified as noreturn.
Change the noreturn detection to consider such cases as effectively
sibling calls, except for one known exception: jumping to .altinstr_aux.
Currently the misclassification is harmless: dead ends aren't marked
when calling a noreturn from an alternative replacement
(CALL_UNTRAIN_RET), they're ignored by rethunk validation, and ORC
generation relies on unwind hints in the SRSO code regardless.
Fix it in the name of robustness and in preparation for a subsequent
patch which generates a list of exported noreturns.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
tools/objtool/check.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 35e24151f5785..41df5f608535f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -266,8 +266,22 @@ static bool might_return(struct objtool_file *file, struct symbol *func)
if (insn->type == INSN_RETURN)
return true;
- if (!is_sibling_call(insn))
+ if (!is_sibling_call(insn)) {
+ /*
+ * Assume a jump into a non-function eventually returns
+ * to the original caller one way or another, e.g., the
+ * jump in srso_alias_untrain_ret().
+ *
+ * .altinstr_aux is an exception, cpu_feature_enabled()
+ * jumps there and then right back.
+ */
+ if (is_static_jump(insn) && insn->jump_dest &&
+ !insn_func(insn->jump_dest) &&
+ strcmp(insn->jump_dest->sec->name, ".altinstr_aux"))
+ return true;
+
continue;
+ }
dest = insn_call_dest(insn);
if (!dest || !is_noreturn(dest))--
2.55.0