linux-kernel - [PATCH v2 7/8] params: use type alignment for kernel parameters

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Date:   Mon, 23 Nov 2020 11:23:18 +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 7/8] params: use type alignment for kernel parameters

Specify type alignment for kernel parameters instead of sizeof(void *).

The alignment attribute is used to prevent gcc from increasing the
alignment of objects with static extent as an optimisation, something
which would mess up the __param array stride.

Using __alignof__(struct kernel_param) rather than sizeof(void *) is
preferred since it better indicates why it is there and doesn't break
should the type size or alignment change.

Note that on m68k the alignment of struct kernel_param is actually two
and that adding a 1- or 2-byte field to the 20-byte struct would cause a
breakage with the current 4-byte alignment.

Signed-off-by: Johan Hovold <johan@...nel.org>
---
 include/linux/moduleparam.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 742074ad9f6e..15ecc6cc3a3b 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -288,8 +288,8 @@ struct kparam_array
 	/* Default value instead of permissions? */			\
 	static const char __param_str_##name[] = prefix #name;		\
 	static struct kernel_param __moduleparam_const __param_##name	\
-	__used								\
-	__section("__param") __attribute__ ((aligned(sizeof(void *))))  \
+	__used __section("__param")					\
+	__aligned(__alignof__(struct kernel_param))			\
 	= { __param_str_##name, THIS_MODULE, ops,			\
 	    VERIFY_OCTAL_PERMISSIONS(perm), level, flags, { arg } }
 
-- 
2.26.2