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From: Andreas Schwab <schwab@linux-m68k.org>
To: Dmitry Torokhov <dtor@vmware.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Rusty Russell <rusty@rustcorp.com.au>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linux/m68k <linux-m68k@vger.kernel.org>,
	Linux-Arch <linux-arch@vger.kernel.org>
Subject: Re: Early crash (was: Re: module: show version information for built-in modules in sysfs)
Date: Wed, 02 Feb 2011 23:52:04 +0100	[thread overview]
Message-ID: <m2ipx2dp7v.fsf@igel.home> (raw)
In-Reply-To: <20110202194227.GA13794@dtor-ws.eng.vmware.com> (Dmitry Torokhov's message of "Wed, 2 Feb 2011 11:42:27 -0800")

Dmitry Torokhov <dtor@vmware.com> writes:

> But why is it aligned on 2-byte boundary and why m64k is not happy with
> module_version_attribute but is happy with kernel_param which is also
> aligned similarly?

struct kernel_parm doesn't contain internal padding on 32 bit
architectures (it does on 64bit architectures though).

> If we unroll module_version_attribute it woud look like this:
>
> struct module_version_attribute {
>
> 	struct module_attribute {
>
> 		struct attribute {
> 			const char *name;
> 			mode_t mode;
> 		} attr;
> 		...
>
> 	} mattr;
>
> 	const char *module_name;
> 	const char *version;
> };
>
> So I would expect it be aligned on (char *) boundary which should be the
> same as (void *).

mode_t is a 16 bit type, thus any following member becomes aligned on an
odd 2 byte boundary.  On 32bit architectures with 4 byte alignment and
16 bit mode_t struct attribute contains 2 bytes of internal padding.
(64bit architectures typically have a 32bit mode_t, and there are 4
bytes of padding.)

> Will it help if we rearrange module_version_attribute definition to
> explicitly have first field being a pointer so it is more like
> kernel_param, like this:
>
> struct module_version_attribute {
> 	const char *module_name;
> 	const char *version;
> 	struct module_attribute mattr;
> };

That won't change the total size of the structure.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

  reply	other threads:[~2011-02-02 22:52 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-02-01 20:33 Geert Uytterhoeven
2011-02-01 21:09 ` Dmitry Torokhov
2011-02-01 22:03   ` Geert Uytterhoeven
2011-02-01 22:26     ` Dmitry Torokhov
2011-02-02 14:48       ` Geert Uytterhoeven
2011-02-02 19:42         ` Dmitry Torokhov
2011-02-02 22:52           ` Andreas Schwab [this message]
2011-02-02 23:59             ` Dmitry Torokhov
2011-02-03  0:10               ` Andreas Schwab
2011-02-03  0:24                 ` Dmitry Torokhov
2011-02-03 17:38                   ` Andreas Schwab
2011-02-07  8:19                   ` Dmitry Torokhov
2011-02-07  8:50                     ` Early crash David Miller
2011-02-07 16:58                       ` Dmitry Torokhov
2011-02-07 19:27                         ` David Miller
2011-02-07 19:28                           ` Dmitry Torokhov
2011-02-08  3:12                           ` Rusty Russell
2011-02-08  3:31                             ` David Miller

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