linux-kernel - Re: [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv

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Message-ID: <4CFF4D4C.2070002@redhat.com>
Date:	Wed, 08 Dec 2010 11:18:04 +0200
From:	Avi Kivity <avi@...hat.com>
To:	David Sharp <dhsharp@...gle.com>
CC:	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	mrubin@...gle.com, kvm-devel <kvm@...r.kernel.org>
Subject: Re: [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv_hypercall

On 12/07/2010 11:16 PM, David Sharp wrote:
> >
> >  I don't understand this.  Can you elaborate?  What does "32-bit addressable"
> >  mean?
>
> The ring buffer gives you space that is a multiple of 4 bytes in
> length, and 32-bit aligned. Therefore it is useless to attempt to
> align the structure beyond 32-bit boundaries, eg, a 64-bit boundary,
> because it is unpredictable if the memory the structure will be
> written to is at a 64-bit boundary (addr % 8 could be 0 or 4).
>
> >  And "predicated on packing the event structures"?  Is the structure
> >  __attribute__((packed)), or is it not?
>
> It is not packed in Linus' tree, but one of the patches before this
> patch in this patch series adds __attribute__((packed)). This patch
> assumes that the event packing patch has been applied. This patch
> should not be applied if the packing patch is not (hence,
> "predicated").

Thanks for the explanations, it makes sense now.

-- 
error compiling committee.c: too many arguments to function

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