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

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Date:   Tue, 15 Sep 2020 10:44:51 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Borislav Petkov <bp@...en8.de>, 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>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e

On Tue, Sep 15, 2020 at 10:02 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Tue, Sep 15, 2020 at 06:05:54PM +0200, Borislav Petkov wrote:
> > On Tue, Sep 15, 2020 at 10:18:16PM +0800, Rong Chen wrote:
> > > On Tue, Sep 15, 2020 at 03:55:19PM +0200, Borislav Petkov wrote:
> > > > On Tue, Sep 15, 2020 at 09:42:56PM +0800, kernel test robot wrote:
> > > > > tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git  x86/seves
> > > > > branch HEAD: e6eb15c9ba3165698488ae5c34920eea20eaa38e  KVM: nSVM: Avoid freeing uninitialized pointers in svm_set_nested_state()
> > > > >
> > > > > Warning in current branch:
> > > > >
> > > > > arch/x86/kernel/sev-es.o: warning: objtool: ist_exc_vmm_communication()+0x12: unreachable instruction
> > > > >
> > > > > Warning ids grouped by kconfigs:
> > > > >
> > > > > clang_recent_errors
> > > > > `-- x86_64-randconfig-r001-20200913
> > > > >     `-- arch-x86-kernel-sev-es.o:warning:objtool:ist_exc_vmm_communication():unreachable-instruction
> >
> > Ok, I can't trigger this with gcc-9, gcc-10 and clang-10.
> >
> > .config below says clang-12 so it could be some experimental
> > bug^Wfeature :)
> >
> > peterz says this has been fixed by:
> >
> > 318af7b80b6a ("Revert "kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled"")
> >
> > but that was reportedly for gcc.
> >
> > Lemme Cc the people of interest and leave the rest in here for
> > reference. Note that CONFIG_LIVEPATCH is enabled in that .config.
>
> If somebody can share the .o file, I can take a look.

I'm cc'ed on and read every report from 0day bot from builds with
Clang.  I started noticing a few randconfigs getting this report from
objtool.  I had filed a bug to follow up on this:
https://github.com/ClangBuiltLinux/linux/issues/1148.  They all seem
to be coming from randconfigs.  I've not yet had the time to bisect
configs to isolate which config this is coming from, but I wouldn't be
surprised if it was UBSAN.

-- 
Thanks,
~Nick Desaulniers