linux-kernel - Re: [PATCH] USB: ehci: use packed,aligned(4) instead of removing the packed attribute

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Message-ID: <Pine.LNX.4.44L0.1106211054460.2327-100000@iolanthe.rowland.org>
Date:	Tue, 21 Jun 2011 10:58:19 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Nicolas Pitre <nico@...xnic.net>
cc:	Alexander Holler <holler@...oftware.de>,
	Arnd Bergmann <arnd@...db.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-usb@...r.kernel.org>, <gregkh@...e.de>,
	lkml <linux-kernel@...r.kernel.org>, Rabin Vincent <rabin@....in>
Subject: Re: [PATCH] USB: ehci: use packed,aligned(4) instead of removing
 the packed attribute

On Mon, 20 Jun 2011, Nicolas Pitre wrote:

> > We don't fall into any of these cases, and therefore as you say, we
> > don't need packed.  Arnd and I have both explained this.  So why do you 
> > keep arguing that we do need it?
> 
> Please show me where I keep arguing that you need it?

Not explicitly perhaps.  But you did write:

> Doesn't mean that because it used to work that it is strictly correct.  
> Wouldn't be the first time that a GCC upgrade broke the kernel because 
> the kernel wasn't describing things properly enough.

which strongly implies that "packed" is needed.  You also wrote:

> Yes, but that's a consequence of not being able to access those fields 
> in their naturally aligned position anymore.  Hence the addition of the 
> align attribute to tell the compiler that we know that the structure is 
> still aligned to a certain degree letting the compiler to avoid 
> byte-oriented instructions when possible.

which is predicated on the assumption that "packed" is needed.

Alan Stern

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