linux-kernel - [PATCH v2 4/8] module: simplify version-attribute handling

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Date:   Mon, 23 Nov 2020 11:23:15 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        David Miller <davem@...emloft.net>,
        Jakub Jelinek <jakub@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Kurtz <djkurtz@...omium.org>,
        linux-arch@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>
Subject: [PATCH v2 4/8] module: simplify version-attribute handling

Instead of using the array-of-pointers trick to avoid having gcc mess up
the built-in module-version array stride, specify type alignment when
declaring entries to prevent gcc from increasing alignment.

This is essentially an alternative (one-line) fix to the problem
addressed by commit b4bc842802db ("module: deal with alignment issues in
built-in module versions").

gcc can increase the alignment of larger objects with static extent as
an optimisation, but this can be suppressed by using the aligned
attribute when declaring variables.

Note that we have been relying on this behaviour for kernel parameters
for 16 years and it indeed hasn't changed since the introduction of the
aligned attribute in gcc-3.1.

Signed-off-by: Johan Hovold <johan@...nel.org>
---
 include/linux/module.h | 26 +++++++++++++-------------
 kernel/params.c        | 10 ++++------
 2 files changed, 17 insertions(+), 19 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 735f2931ea47..ebe2641d7b0b 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -266,20 +266,20 @@ extern typeof(name) __mod_##type##__##name##_device_table		\
 #else
 #define MODULE_VERSION(_version)					\
 	MODULE_INFO(version, _version);					\
-	static struct module_version_attribute ___modver_attr = {	\
-		.mattr	= {						\
-			.attr	= {					\
-				.name	= "version",			\
-				.mode	= S_IRUGO,			\
+	static struct module_version_attribute __modver_attr		\
+		__used __section("__modver")				\
+		__aligned(__alignof__(struct module_version_attribute)) \
+		= {							\
+			.mattr	= {					\
+				.attr	= {				\
+					.name	= "version",		\
+					.mode	= S_IRUGO,		\
+				},					\
+				.show	= __modver_version_show,	\
 			},						\
-			.show	= __modver_version_show,		\
-		},							\
-		.module_name	= KBUILD_MODNAME,			\
-		.version	= _version,				\
-	};								\
-	static const struct module_version_attribute			\
-	__used __section("__modver")					\
-	* __moduleparam_const __modver_attr = &___modver_attr
+			.module_name	= KBUILD_MODNAME,		\
+			.version	= _version,			\
+		};
 #endif
 
 /* Optional firmware file (or files) needed by the module
diff --git a/kernel/params.c b/kernel/params.c
index 164d79330849..2daa2780a92c 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -843,18 +843,16 @@ ssize_t __modver_version_show(struct module_attribute *mattr,
 	return scnprintf(buf, PAGE_SIZE, "%s\n", vattr->version);
 }
 
-extern const struct module_version_attribute *__start___modver[];
-extern const struct module_version_attribute *__stop___modver[];
+extern const struct module_version_attribute __start___modver[];
+extern const struct module_version_attribute __stop___modver[];
 
 static void __init version_sysfs_builtin(void)
 {
-	const struct module_version_attribute **p;
+	const struct module_version_attribute *vattr;
 	struct module_kobject *mk;
 	int err;
 
-	for (p = __start___modver; p < __stop___modver; p++) {
-		const struct module_version_attribute *vattr = *p;
-
+	for (vattr = __start___modver; vattr < __stop___modver; vattr++) {
 		mk = locate_module_kobject(vattr->module_name);
 		if (mk) {
 			err = sysfs_create_file(&mk->kobj, &vattr->mattr.attr);
-- 
2.26.2