linux-kernel - Re: [PATCH] modpost: add an option to suppress 'exported twice' warnings

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Date:   Wed, 06 Nov 2019 09:34:02 -0500
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-kbuild@...r.kernel.org,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] modpost: add an option to suppress 'exported twice' warnings

Masahiro Yamada <yamada.masahiro@...ionext.com> writes:

> Since commit "modpost: do not set ->preloaded for symbols from
> Module.symvers", the modpost always warns about symbols exported
> multiple times.
>
> Generally, I believe it is a good thing to show a warning when the
> same symbol name is exported twice. This avoids the accidental symbol
> conflict.
>
> However, in some cases, we build an external module to provide a
> different version/variant of the in-kernel module, overriding the
> same set of exported symbols.
>
> At least, there is one use-case in the upstream code;
> tools/testing/nvdimm/libnvdimm.ko replaces drivers/nvdimm/libnvdimm.ko
> in order to link it against mocked version of core kernel symbols.
>
> Now, this emits a lots of 'exported twice' warnings:
>
>   https://lkml.org/lkml/2019/10/31/627
>
> To suppress those, add a new option KBUILD_DUPLICATED_EXPORTS_NO_WARN.
>
> If you intentionally override the existing symbols, you can pass it
> from the command line:
>
>   make M=tools/testing/nvdimm KBUILD_DUPLICATED_EXPORTS_NO_WARN=1
>
> Or, more conveniently, you can add it to the module Makefile, so
> you can still do:
>
>   make M=tools/testing/nvdimm
>
> without sprinkling the warnings.
>
> Reported-by: Jeff Moyer <jmoyer@...hat.com>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
> Jeff Moyer,
> Dan Williams,
>
> Please check if this patch solves the nvdimm build issue.

Yep, that fixes it for me.

You can add:

Tested-by: Jeff Moyer <jmoyer@...hat.com>

Thanks!