linux-kernel - Re: [RFC 0/6] Regressions for "imply" behavior change

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Date:   Wed, 8 Apr 2020 16:38:29 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Arnd Bergmann <arnd@...db.de>
cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [RFC 0/6] Regressions for "imply" behavior change

On Wed, 8 Apr 2020, Arnd Bergmann wrote:

> Hi everyone,
> 
> I've just restarted doing randconfig builds on top of mainline Linux and
> found a couple of regressions with missing dependency from the recent
> change in the "imply" keyword in Kconfig, presumably these two patches:
> 
> 3a9dd3ecb207 kconfig: make 'imply' obey the direct dependency
> def2fbffe62c kconfig: allow symbols implied by y to become m
> 
> I have created workarounds for the Kconfig files, which now stop using
> imply and do something else in each case. I don't know whether there was
> a bug in the kconfig changes that has led to allowing configurations that
> were not meant to be legal even with the new semantics, or if the Kconfig
> files have simply become incorrect now and the tool works as expected.

In most cases it is the code that has to be fixed. It typically does:

	if (IS_ENABLED(CONFIG_FOO))
		foo_init();

Where it should rather do:

	if (IS_REACHABLE(CONFIG_FOO))
		foo_init();

A couple of such patches have been produced and queued in their 
respective trees already.


Nicolas