MIME-Version: 1.0
References: <20230225014529.2259752-1-davidgow@google.com>
In-Reply-To: <20230225014529.2259752-1-davidgow@google.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 27 Feb 2023 14:43:27 -0800
Message-ID: <CAHk-=wgK07PQ_DBBbAbSJ41t__6de1xZ6q7RRu-JS=2SU0wqLQ@mail.gmail.com>
Subject: Re: [PATCH] kunit: Fix 'hooks.o' build by recursing into kunit
To:     David Gow <davidgow@google.com>
Cc:     Shuah Khan <skhan@linuxfoundation.org>,
        Brendan Higgins <brendan.higgins@linux.dev>,
        Rae Moar <rmoar@google.com>,
        Daniel Latypov <dlatypov@google.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Feb 24, 2023 at 5:45=E2=80=AFPM David Gow <davidgow@google.com> wro=
te:
>
> +# Some KUnit files (hooks.o) need to be built-in even when KUnit is a mo=
dule,
> +# so we can't just use obj-$(CONFIG_KUNIT).
> +ifdef CONFIG_KUNIT
> +obj-y +=3D kunit/
>  endif

We actually have a pattern for this, although I guess it's rare enough
that "pattern" isn't necessarily the right word.

But you can find things like the Hyper-V drivers having similar
issues, and so the driver Makefile has

    obj-$(subst m,y,$(CONFIG_HYPERV))       +=3D hv/

See a few other cases with

    git grep "subst m,y,"

but I guess the "ifdef CONFIG_KUNIT" thing works too. I can only find
one case of that (in arch/mips/Kbuild).

Another way of dealing with this - that is more common for individual
object files rather than directories - is to just do

    kunit-dir-$(CONFIG_KUNIT) :=3D kunit/
    obj-y +=3D $(kunit-dir-y) $(kunit-dir-m)

which admittedly is also not a hugely common pattern, but does exist
in various places (see for example the 'sfp-bus.o' file and CONFIG_SFP
in drivers/net/phy/Makefile.

That last pattern is probably most common in scripts/Makefile.lib,
where we have things like

       hostprogs +=3D $(hostprogs-always-y) $(hostprogs-always-m)

which is similar but not the exact same thing.

Anyway, I guess I'll just apply that patch as-is, I just wanted to
point out that the particular pattern it uses may be simple, but we've
generally tried to just do our Makefile evaluations with "arithmetic"
rather than conditionals.

              Linus