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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20181127184835.GA5147@rkaganip.lan>
Date:   Tue, 27 Nov 2018 18:48:42 +0000
From:   Roman Kagan <rkagan@...tuozzo.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
CC:     "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>
Subject: Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures
 definitions to hyperv-tlfs.h

On Tue, Nov 27, 2018 at 02:10:49PM +0100, Vitaly Kuznetsov wrote:
> Roman Kagan <rkagan@...tuozzo.com> writes:
> > On Mon, Nov 26, 2018 at 04:47:29PM +0100, Vitaly Kuznetsov wrote:
> > I personally tend to prefer masks over bitfields, so I'd rather do the
> > consolidation in the opposite direction: use the definitions in
> > hyperv-tlfs.h and replace those unions/bitfields elsewhere.  (I vaguely
> > remember posting such a patchset a couple of years ago but I lacked the
> > motivation to complete it).
> 
> Are there any known advantages of using masks over bitfields or the
> resulting binary code is the same?

Strictly speaking bitwise ops are portable while bitfields are not, but
I guess this is not much of an issue with gcc which is dependable to
produce the right thing.

I came to dislike the bitfields for the false feeling of atomicity of
assignment while most of the time they are read-modify-write operations.

And no, I don't feel strong about it, so if nobody backs me on this I
give up :)

Roman.