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

From: Nadav Amit
Date: Wed Nov 28 2018 - 12:55:44 EST

> On Nov 28, 2018, at 5:07 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> On Wed, 28 Nov 2018, Vitaly Kuznetsov wrote:
>> Nadav Amit <nadav.amit@xxxxxxxxx> writes:
>>> On a different note: how come all of the hyper-v structs are not marked
>>> with the âpacked" 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.

Right, I forgot about the structs randomization. So at least for it, the
attribute should be needed.

To prevent conflicts, I think that this series should also add the
attribute in a first patch, which would be tagged for stable.