eval.c: reduce machine stack overflow backtrace

* eval.c (setup_exception): revert r46531 to reduce backtrace at
  machine stack overflow.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46589 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

eval.c

@@ -492,7 +492,19 @@ setup_exception(rb_thread_t *th, int tag, volatile VALUE mesg, VALUE cause)
     file = rb_sourcefile();
     if (file) line = rb_sourceline();
     if (file && !NIL_P(mesg)) {
-	if (sysstack_error_p(mesg) || NIL_P(at = get_backtrace(mesg))) {
+	if (mesg == sysstack_error) {
+	    /* machine stack overflow, reduce too long backtrace */
+	    ID func = rb_frame_this_func();
+	    at = rb_enc_sprintf(rb_usascii_encoding(), "%s:%d", file, line);
+	    if (func) {
+		VALUE name = rb_id2str(func);
+		if (name) rb_str_catf(at, ":in `%"PRIsVALUE"'", name);
+	    }
+	    at = rb_ary_new3(1, at);
+	    mesg = rb_obj_dup(mesg);
+	    rb_iv_set(mesg, "bt", at);
+	}
+	else if (sysstack_error_p(mesg) || NIL_P(at = get_backtrace(mesg))) {
 	    at = rb_vm_backtrace_object();
 	    if (OBJ_FROZEN(mesg)) {
 		mesg = rb_obj_dup(mesg);