linux-kernel - Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e

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Message-ID: <20200915224401.GA1156663@rani.riverdale.lan>
Date:   Tue, 15 Sep 2020 18:44:01 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Rong Chen <rong.a.chen@...el.com>,
        kernel test robot <lkp@...el.com>,
        "Li, Philip" <philip.li@...el.com>, x86-ml <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Marco Elver <elver@...gle.com>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING
 e6eb15c9ba3165698488ae5c34920eea20eaa38e

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@...m.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