linux-kernel - Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO

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: <20171116174830.GX3624@linux.vnet.ibm.com>
Date:   Thu, 16 Nov 2017 09:48:30 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Alex Matveev <alxmtvv@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 18/18] arm64: select ARCH_SUPPORTS_LTO_CLANG

On Thu, Nov 16, 2017 at 06:34:17PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 16, 2017 at 09:16:49AM -0800, Nick Desaulniers wrote:
> > On Thu, Nov 16, 2017 at 8:59 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > > On Thu, Nov 16, 2017 at 08:50:41AM -0800, Nick Desaulniers wrote:
> > >> On Thu, Nov 16, 2017 at 8:30 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > >>
> > >> > Ideally we'd get the toolchain people to commit to supporting the kernel
> > >> > memory model along side the C11 one. That would help a ton.
> > >>
> > >> Does anyone from the kernel side participate in the C standardization process?
> > >
> > > Yes, Paul McKenney and Will Deacon. Doesn't mean these two can still be
> > > reconciled though. From what I understand C11 (and onwards) are
> > > incompatible with the kernel model on a number of subtle points.
> > 
> > It would be good to have these incompatibilities written down, then
> > for the sake of argument, they can be cited both for discussions on
> > LKML and in the C standardization process.  For example, a running
> > list in Documentation/ or something would make it so that anyone could
> > understand and cite current issues with the latest C standard.
> 
> Will should be able to produce this list; I know he's done before, I
> just can't find it -- my Google-foo isn't strong today.

Here you go:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0124r4.html

> > I don't understand why we'd block patches for enabling experimental
> > features.  We've been running this patch-set on actual devices for
> > months and would love to provide them to the community for further
> > testing.  If bugs are found, then there's more evidence to bring to
> > the C standards committee.  Otherwise we're shutting down feature
> > development for the sake of potential bugs in a C standard we're not
> > even using.
> 
> So the problem is that its very very hard (and painful) to find these
> bugs. Getting the tools people to comment on these specific
> optimizations would really help lots.

It would be good to get something similar to LKMM into KTSAN, for
example.  There would probably be a few differences due to efficiency
concerns, but closer is better than less close.  ;-)

							Thanx, Paul