modpost: make sym_add_exported() always allocate a new symbol

Currently, sym_add_exported() does not allocate a symbol if the same
name symbol already exists in the hash table.

This does not reflect the real use cases. You can let an external
module override the in-tree one. In this case, the external module
will export the same name symbols as the in-tree one. However,
modpost simply ignores those symbols, then Module.symvers for the
external module loses its symbols.

sym_add_exported() should allocate a new symbol.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/mod/modpost.c

@@ -412,19 +412,17 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
 {
 	struct symbol *s = find_symbol(name);
 
-	if (!s) {
-		s = new_symbol(name, mod, export);
-		list_add_tail(&s->list, &mod->exported_symbols);
-	} else if (!external_module || s->module->is_vmlinux ||
-		   s->module == mod) {
+	if (s && (!external_module || s->module->is_vmlinux || s->module == mod)) {
 		error("%s: '%s' exported twice. Previous export was in %s%s\n",
 		      mod->name, name, s->module->name,
 		      s->module->is_vmlinux ? "" : ".ko");
-		return s;
 	}
 
+	s = new_symbol(name, mod, export);
 	s->module = mod;
 	s->export    = export;
+	list_add_tail(&s->list, &mod->exported_symbols);
+
 	return s;
 }