linux-kernel - Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures definitions to hyperv-tlfs.h

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Date:   Wed, 28 Nov 2018 14:07:42 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
cc:     Nadav Amit <nadav.amit@...il.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Roman Kagan <rkagan@...tuozzo.com>
Subject: Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures
 definitions to hyperv-tlfs.h

On Wed, 28 Nov 2018, Vitaly Kuznetsov wrote:

> Nadav Amit <nadav.amit@...il.com> writes:
> 
> >
> > On a different note: how come all of the hyper-v structs are not marked
> > with the “packed" attribute?
> 
> "packed" should not be needed with proper padding; I vaguely remember
> someone (from x86@?) arguing _against_ "packed".

Packed needs to be used, when describing fixed format data structures in
hardware or other ABIs, so the compiler cannot put alignment holes into
them.

Using packed for generic data structures might result in suboptimal layouts
and prevents layout randomization.

Thanks,

	tglx