Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Tue, 15 Sep 2020 18:44:01 -0400
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        Borislav Petkov <bp@alien8.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Rong Chen <rong.a.chen@intel.com>,
        kernel test robot <lkp@intel.com>,
        "Li, Philip" <philip.li@intel.com>, x86-ml <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Marco Elver <elver@google.com>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING
 e6eb15c9ba3165698488ae5c34920eea20eaa38e
Message-ID: <20200915224401.GA1156663@rani.riverdale.lan>
References: <5f60c4e0.Ru0MTgSE9A7mqhpG%lkp@intel.com>
 <20200915135519.GJ14436@zn.tnic>
 <20200915141816.GC28738@shao2-debian>
 <20200915160554.GN14436@zn.tnic>
 <20200915170248.gcv54pvyckteyhk3@treble>
 <CAKwvOdnc8au10g8q8miab89j3tT8UhwnZOMAJdRgkXVrnkhwqQ@mail.gmail.com>
 <20200915204912.GA14436@zn.tnic>
 <20200915215054.GA1104608@rani.riverdale.lan>
 <CAKwvOdnctit9cQ9Na8kO5TXbZh-3ZV5x1=GLHhRVdBUK23HjnA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAKwvOdnctit9cQ9Na8kO5TXbZh-3ZV5x1=GLHhRVdBUK23HjnA@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Sep 15, 2020 at 02:59:19PM -0700, Nick Desaulniers wrote:
> On Tue, Sep 15, 2020 at 2:50 PM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > On Tue, Sep 15, 2020 at 10:49:12PM +0200, Borislav Petkov wrote:
> > >
> > > (Btw, clang doesn't need to add that "xor %eax,%eax" - panic() should not be
> > >  returning, ever. :-))
> > >
> >
> > I think this is because panic() is varargs, and clang doesn't support
> > gcc's -mskip-rax-setup. The normal ABI requires the caller to set RAX to
> > the number of arguments in vector registers.
> >
> > https://patchwork.ozlabs.org/project/gcc/patch/20141218131150.GA32638@intel.com/
> 
> Thanks for the report.  Filed
> https://bugs.llvm.org/show_bug.cgi?id=47538.  Do you have an account
> there Arvind so that I can CC you on them?

Nope, no bugzilla account.

If you're adding flags, another set the kernel uses is the
-falign-{jumps,labels,loops} to turn off alignment of jumps and loops.

> 
> Yikes, it looks like gcc 5.0 supports that.  We'd better get to
> implementing that lest someone try to remove the cc-option on it soon.
> -- 
> Thanks,
> ~Nick Desaulniers