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From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Tue, 15 Sep 2020 17:50:54 -0400
To:     Borislav Petkov <bp@alien8.de>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        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: <20200915215054.GA1104608@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>
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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/