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

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Message-ID: <20210609110531.GA1528247@roeck-us.net>
Date:   Wed, 9 Jun 2021 04:05:31 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Arnd Bergmann <arnd@...db.de>,
        David Brazdil <dbrazdil@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Mikhail Petrov <Mikhail.Petrov@....dev>,
        linux-kernel@...r.kernel.org, mfaltesek@...gle.com
Subject: Re: [PATCH] kallsyms: fix nonconverging kallsyms table with lld

Hi Arnd,

On Thu, Feb 04, 2021 at 04:29:47PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> ARM randconfig builds with lld sometimes show a build failure
> from kallsyms:
> 
>   Inconsistent kallsyms data
>   Try make KALLSYMS_EXTRA_PASS=1 as a workaround
> 
> The problem is the veneers/thunks getting added by the linker extend
> the symbol table, which in turn leads to more veneers being needed,
> so it may take a few extra iterations to converge.
> 
> This bug has been fixed multiple times before, but comes back every time
> a new symbol name is used. lld uses a different set of idenitifiers from
> ld.bfd, so the additional ones need to be added as well.
> 
> I looked through the sources and found that arm64 and mips define similar
> prefixes, so I'm adding those as well, aside from the ones I observed. I'm
> not sure about powerpc64, which seems to already be handled through a
> section match, but if it comes back, the "__long_branch_" and "__plt_"
> prefixes would have to get added as well.
> 

This is such a whack-a-mole. The problem is hitting us yet again. I suspect
it may be due to a new version of lld using new symbols, but I didn't really
try to track it down. Is there an easy way to search for missed symbols ?

In this context .. is there a chance to apply [1] after all ? This is getting
really time consuming and annoying, and I really dislike having to fix the same
problem over and over again.

Thanks,
Guenter

---
[1] https://patchwork.kernel.org/project/linux-kbuild/patch/20200910153204.156871-1-linux@roeck-us.net/