From patchwork Tue Dec 8 16:48:20 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Cercueil X-Patchwork-Id: 11959073 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A612CC433FE for ; Tue, 8 Dec 2020 16:49:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6105C23A79 for ; Tue, 8 Dec 2020 16:49:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729948AbgLHQtb (ORCPT ); Tue, 8 Dec 2020 11:49:31 -0500 Received: from aposti.net ([89.234.176.197]:60800 "EHLO aposti.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726703AbgLHQta (ORCPT ); Tue, 8 Dec 2020 11:49:30 -0500 From: Paul Cercueil To: Linus Walleij Cc: Arnd Bergmann , od@zcrc.me, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, Paul Cercueil Subject: [PATCH 1/2] if_enabled.h: Add IF_ENABLED_OR_ELSE() and IF_ENABLED() macros Date: Tue, 8 Dec 2020 16:48:20 +0000 Message-Id: <20201208164821.2686082-1-paul@crapouillou.net> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Introduce a new header , that brings two new macros: IF_ENABLED_OR_ELSE() and IF_ENABLED(). IF_ENABLED_OR_ELSE(CONFIG_FOO, a, b) evaluates to (a) if CONFIG_FOO is set to 'y' or 'm', (b) otherwise. It is used internally to define the IF_ENABLED() macro. The (a) and (b) arguments must be of the same type. IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set to 'y' or 'm', NULL otherwise. The (ptr) argument must be a pointer. The IF_ENABLED() macro can be very useful to help GCC drop dead code. For instance, consider the following: #ifdef CONFIG_FOO_SUSPEND static int foo_suspend(struct device *dev) { ... } #endif static struct pm_ops foo_ops = { #ifdef CONFIG_FOO_SUSPEND .suspend = foo_suspend, #endif }; While this works, the foo_suspend() macro is compiled conditionally, only when CONFIG_FOO_SUSPEND is set. This is problematic, as there could be a build bug in this function, we wouldn't have a way to know unless the config option is set. An alternative is to declare foo_suspend() always, but mark it as maybe unused: static int __maybe_unused foo_suspend(struct device *dev) { ... } static struct pm_ops foo_ops = { #ifdef CONFIG_FOO_SUSPEND .suspend = foo_suspend, #endif }; Again, this works, but the __maybe_unused attribute is required to instruct the compiler that the function may not be referenced anywhere, and is safe to remove without making a fuss about it. This makes the programmer responsible for tagging the functions that can be garbage-collected. With this patch, it is now possible to write the following: static int foo_suspend(struct device *dev) { ... } static struct pm_ops foo_ops = { .suspend = IF_ENABLED(CONFIG_FOO_SUSPEND, foo_suspend), }; The foo_suspend() function will now be automatically dropped by the compiler, and it does not require any specific attribute. Signed-off-by: Paul Cercueil --- include/linux/if_enabled.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) create mode 100644 include/linux/if_enabled.h diff --git a/include/linux/if_enabled.h b/include/linux/if_enabled.h new file mode 100644 index 000000000000..8189d1402340 --- /dev/null +++ b/include/linux/if_enabled.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __LINUX_IF_ENABLED_H +#define __LINUX_IF_ENABLED_H + +#include +#include +#include + +/* + * IF_ENABLED_OR_ELSE(CONFIG_FOO, a, b) evaluates to (a) if CONFIG_FOO is set + * to 'y' or 'm', (b) otherwise. + */ +#define IF_ENABLED_OR_ELSE(option, a, b) \ + (BUILD_BUG_ON_ZERO(__same_type((a), (b))) || IS_ENABLED(option) ? (a) : (b)) + +/* + * IF_ENABLED(CONFIG_FOO, ptr) evaluates to (ptr) if CONFIG_FOO is set to 'y' + * or 'm', NULL otherwise. + */ +#define IF_ENABLED(option, ptr) IF_ENABLED_OR_ELSE(option, ptr, NULL) + +#endif /* __LINUX_IF_ENABLED_H */