linux-kernel - Re: [PATCH 4/5] kbuild: disable KBUILD

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Date:   Wed, 04 Jul 2018 08:14:28 +1000
From:   NeilBrown <neilb@...e.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH 4/5] kbuild: disable KBUILD_MODNAME when building for mod.a

On Wed, Jun 27 2018, Masahiro Yamada wrote:

> 2018-06-18 13:55 GMT+09:00 NeilBrown <neilb@...e.com>:
>> When building an object to be included in mod.a we
>> cannot know the name of the module.  So don't define
>> KBUILD_MODNAME.  This will ensure attempt to use
>> that macro when the module name isn't know will
>> trigger an error.
>
> Honestly, I hate KBUILD_MODNAME.
>
> If KBUILD_MODNAME is undefined,
> you cannot call pr_debug() in the sub-directory for example.

I think this is only true if you have something like

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

in your .c files.  Developers who use modobj-m could be advised not to
do this.

>
> CONFIG_DYNAMIC_DEBUG requires KBUILD_MODNAME,
> but people often miss to notice that, then cause build errors.

Yes, I can see that.
We could change it to use a default ("no-name") if KBUILD_MODNAME isn't
defined.  Or we could require that KBUILD_MODNAME always be defined.

Where I've been using these patches I've sometimes been adding

  ccflags-y += -DKBUILD_MODNAME='"FOO"'

to Makefiles so that modules_params get handled correctly on non-module
builds.  I've thought about instead allowing "modobj-name" to be defined
and requiring that it be set if either modobj-[yn] is set.  Then it gets
used for the KBUILD_MODNAME when building modobj modules.

Would you prefer to always require KBUILD_MODNAME, or to use a default
name for dynamic-debug?

Thanks,
NeilBrown

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