linux-kernel - Re: [PATCH] kallsyms: fix nonconverging kallsyms table with lld

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Message-ID: <20210621114752.GA116119@roeck-us.net>
Date:   Mon, 21 Jun 2021 04:47:52 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        David Brazdil <dbrazdil@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Mikhail Petrov <Mikhail.Petrov@....dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marty Faltesek <mfaltesek@...gle.com>
Subject: Re: [PATCH] kallsyms: fix nonconverging kallsyms table with lld

On Thu, Jun 10, 2021 at 02:26:50PM +0200, Arnd Bergmann wrote:
> On Thu, Jun 10, 2021 at 2:05 PM Guenter Roeck <linux@...ck-us.net> wrote:
> > On Wed, Jun 09, 2021 at 10:30:23PM +0200, Arnd Bergmann wrote:
> > > > I thought I'd see the added symbols, but it looks like the only difference
> > > > between the two files is the addresses.
> > > >
> > > > What am I missing ?
> > >
> > > I probably misremembered the part about 'objdump --syms' and there was
> > > something more to it.
> > >
> > > Maybe this was the last version before converging? It looks like the '<' version
> > > has one extra symbol ompared to the '>' version. The diff has no context, but I
> >
> > It is the difference between step 1 and 2. Why would diff on objdump not
> > show the additional symbol ? Is it possible that the symbol is not added
> > to the object file ?
> 
> Note sure. The symbol must be in the object file, but perhaps the
> 'objdump --syms' output skips a different set of symbols compared
> to the list that is used as input for kallsyms, which comes from '${NM}'.
> 
> Comparing the nm output might be another thing to try.
> 
Just following up on this: As Murphy would have told us, the problem
disappeared while trying to track it down. We'll add some instrumentation
into the ChromeOS kernel build to get data once/if/when it shows up again.
When that happens, we'll try to come up with a patch to show the symbol
file differences in the kernel build and submit it upstream.

Thanks,
Guenter