@@ -220,6 +220,29 @@ static int resolve_relative_url_test(int argc, const char **argv, const char *pr
 	return 0;
 }
 
+/* the result should be freed by the caller. */
+static char *get_submodule_displaypath(const char *path, const char *prefix)
+{
+	const char *super_prefix = get_super_prefix();
+
+	if (prefix && super_prefix) {
+		BUG("cannot have prefix '%s' and superprefix '%s'",
+		    prefix, super_prefix);
+	} else if (prefix) {
+		struct strbuf sb = STRBUF_INIT;
+		char *displaypath = xstrdup(relative_path(path, prefix, &sb));
+		strbuf_release(&sb);
+		return displaypath;
+	} else if (super_prefix) {
+		int len = strlen(super_prefix);
+		const char *format = (len > 0 && is_dir_sep(super_prefix[len - 1])) ? "%s%s" : "%s/%s";
+
+		return xstrfmt(format, super_prefix, path);
+	} else {
+		return xstrdup(path);
+	}
+}
+
 struct module_list {
 	const struct cache_entry **entries;
 	int alloc, nr;

@@ -335,15 +358,7 @@ static void init_submodule(const char *path, const char *prefix, int quiet)
 	struct strbuf sb = STRBUF_INIT;
 	char *upd = NULL, *url = NULL, *displaypath;
 
-	if (prefix && get_super_prefix())
-		die("BUG: cannot have prefix and superprefix");
-	else if (prefix)
-		displaypath = xstrdup(relative_path(path, prefix, &sb));
-	else if (get_super_prefix()) {
-		strbuf_addf(&sb, "%s%s", get_super_prefix(), path);
-		displaypath = strbuf_detach(&sb, NULL);
-	} else
-		displaypath = xstrdup(path);
+	displaypath = get_submodule_displaypath(path, prefix);
 
 	sub = submodule_from_path(&null_oid, path);
 

@@ -358,9 +373,9 @@ static void init_submodule(const char *path, const char *prefix, int quiet)
 	 * Set active flag for the submodule being initialized
 	 */
 	if (!is_submodule_active(the_repository, path)) {
-		strbuf_reset(&sb);
 		strbuf_addf(&sb, "submodule.%s.active", sub->name);
 		git_config_set_gently(sb.buf, "true");
+		strbuf_reset(&sb);
 	}
 
 	/*

@@ -368,7 +383,6 @@ static void init_submodule(const char *path, const char *prefix, int quiet)
 	 * To look up the url in .git/config, we must not fall back to
 	 * .gitmodules, so look it up directly.
 	 */
-	strbuf_reset(&sb);
 	strbuf_addf(&sb, "submodule.%s.url", sub->name);
 	if (git_config_get_string(sb.buf, &url)) {
 		if (!sub->url)

@@ -405,9 +419,9 @@ static void init_submodule(const char *path, const char *prefix, int quiet)
 				_("Submodule '%s' (%s) registered for path '%s'\n"),
 				sub->name, url, displaypath);
 	}
+	strbuf_reset(&sb);
 
 	/* Copy "update" setting when it is not set yet */
-	strbuf_reset(&sb);
 	strbuf_addf(&sb, "submodule.%s.update", sub->name);
 	if (git_config_get_string(sb.buf, &upd) &&
 	    sub->update_strategy.type != SM_UPDATE_UNSPECIFIED) {