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From: Greg KH <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>
To: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
Cc: Andreas Werner <andreas.werner-csrFAY9JiS4@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	johannes.thumshirn-csrFAY9JiS4@public.gmane.org
Subject: Re: [PATCH 1/2] drivers/misc/eeprom/men_eeprod: Introduce MEN Board Information EEPROM driver
Date: Thu, 16 Oct 2014 11:34:14 +0200	[thread overview]
Message-ID: <20141016093414.GA25214@kroah.com> (raw)
In-Reply-To: <20141016085835.GA1273@katana>

On Thu, Oct 16, 2014 at 10:58:35AM +0200, Wolfram Sang wrote:
> > +struct eeprom_data {
> > +	uint8_t eeprod_id;
> > +
> > +	uint8_t revision[3];
> > +	uint32_t serialnr;
> > +	uint8_t board_model;
> > +	char hw_name[6];
> > +
> > +	uint8_t reserved;
> > +
> > +	__be16 prod_date;
> > +	__be16 rep_date;
> > +
> > +	uint8_t reserved2[4];
> > +};
> 
> And what if the compiler reorders?

It's not allowed to reorder, but it can add padding wherever it wants
to, which if this is a on-device structure, can cause problems.  Use
__packed to prevent that.

thanks,

greg k-h

WARNING: multiple messages have this Message-ID (diff)
From: Greg KH <gregkh@linuxfoundation.org>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: Andreas Werner <andreas.werner@men.de>,
	linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
	johannes.thumshirn@men.de
Subject: Re: [PATCH 1/2] drivers/misc/eeprom/men_eeprod: Introduce MEN Board Information EEPROM driver
Date: Thu, 16 Oct 2014 11:34:14 +0200	[thread overview]
Message-ID: <20141016093414.GA25214@kroah.com> (raw)
In-Reply-To: <20141016085835.GA1273@katana>

On Thu, Oct 16, 2014 at 10:58:35AM +0200, Wolfram Sang wrote:
> > +struct eeprom_data {
> > +	uint8_t eeprod_id;
> > +
> > +	uint8_t revision[3];
> > +	uint32_t serialnr;
> > +	uint8_t board_model;
> > +	char hw_name[6];
> > +
> > +	uint8_t reserved;
> > +
> > +	__be16 prod_date;
> > +	__be16 rep_date;
> > +
> > +	uint8_t reserved2[4];
> > +};
> 
> And what if the compiler reorders?

It's not allowed to reorder, but it can add padding wherever it wants
to, which if this is a on-device structure, can cause problems.  Use
__packed to prevent that.

thanks,

greg k-h

  reply	other threads:[~2014-10-16  9:34 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-16  8:14 [PATCH 0/2] Introduce MEN Board Information EEPROM driver Andreas Werner
2014-10-16  8:14 ` Andreas Werner
2014-10-16  8:15 ` [PATCH 1/2] drivers/misc/eeprom/men_eeprod: " Andreas Werner
2014-10-16  8:15   ` Andreas Werner
     [not found]   ` <d169930cfe45d4c05c79f7dd00471d732441529d.1413416105.git.andreas.werner-csrFAY9JiS4@public.gmane.org>
2014-10-16  8:44     ` Greg KH
2014-10-16  8:44       ` Greg KH
2014-10-16 10:11       ` Andreas Werner
2014-10-16 10:11         ` Andreas Werner
2014-10-16  8:58     ` Wolfram Sang
2014-10-16  8:58       ` Wolfram Sang
2014-10-16  9:34       ` Greg KH [this message]
2014-10-16  9:34         ` Greg KH
     [not found]         ` <20141016093414.GA25214-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2014-10-16  9:48           ` Wolfram Sang
2014-10-16  9:48             ` Wolfram Sang
2014-10-16 10:21       ` Andreas Werner
2014-10-16 10:21         ` Andreas Werner
2014-10-16  9:59         ` Wolfram Sang
2014-10-16 11:44           ` Andreas Werner
2014-10-16 11:44             ` Andreas Werner
2014-10-20  8:18             ` Wolfram Sang
2014-10-20  8:18               ` Wolfram Sang
2014-10-20  8:24               ` Wolfram Sang
2014-10-20 10:04                 ` Andreas Werner
2014-10-20 10:04                   ` Andreas Werner
2014-10-20  8:33             ` Andreas Werner
2014-10-20  8:33               ` Andreas Werner
2014-10-20  9:11               ` Greg KH
     [not found]                 ` <20141020091141.GA15332-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>
2014-10-20 10:09                   ` Andreas Werner
2014-10-20 10:09                     ` Andreas Werner
2014-10-21  6:57                     ` Igor Grinberg
2014-10-21  6:57                       ` Igor Grinberg
2014-10-16  8:15 ` [PATCH 2/2] Documentation/ABI/testing/men_eeprod: Added sysfs description for men_eeprod Andreas Werner
2014-10-16  8:15   ` Andreas Werner

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