Re: [PATCH] USB: ehci: use packed,aligned(4) instead of removing thepacked attribute

From: Nicolas Pitre
Date: Tue Jun 21 2011 - 16:42:09 EST

On Tue, 21 Jun 2011, Alan Stern wrote:

> 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:

In this case ...

> > 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.

... and also in this case, I was talking about proper use of the packed
attribute in general, not at all about a specific case. I wanted to
provide a broader view to some people who expressed doubts and
misunderstanding in the hope that the archive could keep this knowledge
base available.

I apologize if that wasn't clear to you.

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