From: Arnd Bergmann <arnd@arndb.de>
To: linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] USB: ehci: use packed,aligned(4) instead of removing the packed attribute
Date: Mon, 20 Jun 2011 22:09:34 +0200
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Cc: Alan Stern <stern@rowland.harvard.edu>,
        Alexander Holler <holler@ahsoftware.de>, gregkh@suse.de,
        Nicolas Pitre <nico@fluxnic.net>, linux-usb@vger.kernel.org,
        lkml <linux-kernel@vger.kernel.org>, Rabin Vincent <rabin@rab.in>
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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.

	Arnd
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