linux-kernel - Re: [tip: objtool/urgent] objtool: Fix seg fault with Clang non-section symbols

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Date:   Fri, 12 Feb 2021 17:40:03 +0800
From:   Xi Ruoyao <xry111@...gyan1223.wang>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "# 3.4.x" <stable@...r.kernel.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip: objtool/urgent] objtool: Fix seg fault with Clang
 non-section symbols

Hi Greg and Nick,

On 2021-02-11 10:46 -0800, Nick Desaulniers wrote:
> On Thu, Feb 11, 2021 at 5:55 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> > 
> > On Thu, Feb 11, 2021 at 09:32:03PM +0800, Xi Ruoyao wrote:
> > > Hi all,
> > > 
> > > The latest GNU assembler (binutils-2.36.1) is removing unused section
> > > symbols
> > > like Clang [1].  So linux-5.10.15 can't be built with binutils-2.36.1
> > > now.  It
> > > has been reported as https://bugzilla.kernel.org/show_bug.cgi?id=211693.
> 
> Xi,
> Happy Lunar New Year to you, too, and thanks for the report.  Did you
> observe such segfaults for older branches of stable?

We found this issue building Linux From Scratch
(http://www.linuxfromscratch.org/lfs/view/development/).  We use the latest
stable kernel in the project so we have no report of older branches.

I tried 5.4.97 with a configuration "looks like" the one triggers the segfault
in 5.10.15.  But 5.4.97 build does not segfault.

However, I guess for "some" config older branches may segfault too.

> > 2.36 of binutils fails to build the 4.4.y tree right now as well, but as
> > objtool isn't there, I don't know what to do about it :(
> 
> Greg,
> There may be multiple issues in the latest binutils release for the
> kernel; we should still avoid segfaults in host tools so I do
> recommend considering this patch for inclusion at least into 5.10.y.

I strongly agree, or it may affect "rolling-release" distros (which are likely
to use binutils-2.36.1 and linux-5.10.y together) in an annoying way.

> Arnd's report in https://github.com/ClangBuiltLinux/linux/issues/1207
> mentions this was found via randconfig testing, so likely some set of
> configs is needed to reproduce reliably.

I attached a config in https://bugzilla.kernel.org/show_bug.cgi?id=211693 (also
attached in this mail).  It reproduces the issue for 5.10.15 very reliably.  At
least three of us tried this configuration on the system personally used (with
binutils-2.36.1) and we got exactly same error: objtool segfaults on apic.o.

> Do you have more info about the failure you're observing? Trolling
> lore, I only see:
> https://lore.kernel.org/stable/YCLeJcQFsDIsrAEc@kroah.com/
> (Maybe it was reported on a different list; I only searched stable ML).

-- 
Xi Ruoyao <xry111@...gyan1223.wang>
School of Aerospace Science and Technology, Xidian University

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