netdev - Re: [PATCH net-next V2] net: ks8851: Fix mixed module/builtin build

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Date:   Sat, 16 Jan 2021 18:04:12 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Marek Vasut <marex@...x.de>
Cc:     Networking <netdev@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>,
        Arnd Bergmann <arnd@...db.de>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH net-next V2] net: ks8851: Fix mixed module/builtin build

On Sat, Jan 16, 2021 at 5:48 PM Marek Vasut <marex@...x.de> wrote:
>
> When either the SPI or PAR variant is compiled as module AND the other
> variant is compiled as built-in, the following build error occurs:
>
> arm-linux-gnueabi-ld: drivers/net/ethernet/micrel/ks8851_common.o: in function `ks8851_probe_common':
> ks8851_common.c:(.text+0x1564): undefined reference to `__this_module'
>
> Fix this by passing THIS_MODULE as argument to ks8851_probe_common(),
> ks8851_register_mdiobus(), and ultimately __mdiobus_register() in the
> ks8851_common.c.
>
> Fixes: ef3631220d2b ("net: ks8851: Register MDIO bus and the internal PHY")
> Signed-off-by: Marek Vasut <marex@...x.de>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Heiner Kallweit <hkallweit1@...il.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Lukas Wunner <lukas@...ner.de>

I don't really like this version, as it does not actually solve the problem of
linking the same object file into both vmlinux and a loadable module, which
can have all kinds of side-effects besides that link failure you saw.

If you want to avoid exporting all those symbols, a simpler hack would
be to '#include "ks8851_common.c" from each of the two files, which
then always duplicates the contents (even when both are built-in), but
at least builds the file the correct way.

       Arnd