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

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Message-ID: <Pine.LNX.4.44L0.1106201704340.2113-100000@iolanthe.rowland.org>
Date:	Mon, 20 Jun 2011 17:05:20 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Arnd Bergmann <arnd@...db.de>
cc:	linux-arm-kernel@...ts.infradead.org,
	Alexander Holler <holler@...oftware.de>, <gregkh@...e.de>,
	Nicolas Pitre <nico@...xnic.net>, <linux-usb@...r.kernel.org>,
	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, Arnd Bergmann wrote:

> On Monday 20 June 2011 20:39:02 Alan Stern wrote:
> > On Mon, 20 Jun 2011, Alexander Holler wrote:
> > 
> > > I see it that way: packed is needed to be sure that at least for struct 
> > > ehci_regs there are no padding bytes inbetween the members.
> > 
> > But is it really needed?
> 
> No. When the structure is marked packed, it's broken because it relies
> on undefined behavior. If it's not packed, there is no problem.
> 
> > > It might 
> > > work without, but that depends on the compiler (-version, architecture, 
> > > whatever).
> > 
> > Have there ever been any combinations of compiler, version, 
> > architecture, whatever, that had unwanted padding bytes in this 
> > structure?
> 
> Only on compilers that are not able to build Linux kernels anyway.

Just as I thought.  There's no reason to accept the proposed patch; 
we're fine the way we are now.

Alan Stern

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