Re: [PATCH] lib/math/rational.c: Fix divide by zero

From: Daniel Latypov <dlatypov@google.com>
To: Randy Dunlap <rdunlap@infradead.org>
Cc: Andy Shevchenko <andriy.shevchenko@intel.com>,
	Trent Piepho <tpiepho@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	andy@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	Oskar Schirmer <oskar@scara.com>, Yiyuan Guo <yguoaz@gmail.com>
Subject: Re: [PATCH] lib/math/rational.c: Fix divide by zero
Date: Mon, 24 May 2021 15:56:25 -0700	[thread overview]
Message-ID: <CAGS_qxrZAxvRD5Scvd-dMahnf-27npMjbzKKjG-+Bk7hZgZj5g@mail.gmail.com> (raw)
In-Reply-To: <b5511f68-814b-1f8c-08d2-a7dbddce4e8d@infradead.org>

On Mon, May 24, 2021 at 3:04 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> On 5/24/21 9:55 AM, Daniel Latypov wrote:
> > diff --git a/lib/math/Kconfig b/lib/math/Kconfig
> > index f19bc9734fa7..20460b567493 100644
> > --- a/lib/math/Kconfig
> > +++ b/lib/math/Kconfig
> > @@ -15,3 +15,14 @@ config PRIME_NUMBERS
> >
> >  config RATIONAL
> >         bool
> > +
> > +config RATIONAL_KUNIT_TEST
> > +       tristate "KUnit test for rational number support" if !KUNIT_ALL_TESTS
> > +       # depends on KUNIT && RATIONAL  # this is how it should work, but
> > +       depends on KUNIT
> > +       select RATIONAL # I don't grok kconfig enough to know why this
>
> Only to set the symbol CONFIG_RATIONAL.
> Then when 'make' descends into the lib/math/ subdir and looks at its Makefile,
> it will decide to build the binary rational.o.
>
> obj-$(CONFIG_RATIONAL)          += rational.o
>

Ack, I understand that much.

My confusion is why this doesn't work:

$ ./tools/testing/kunit/kunit.py run --kunitconfig /dev/stdin <<EOF
CONFIG_KUNIT=y
CONFIG_RATIONAL=y
EOF
...
ERROR:root:Provided Kconfig is not contained in validated .config.
Following fields found in kunitconfig, but not in .config:
CONFIG_RATIONAL=y

What it's complaining about is that `make  ARCH=um olddefconfig` is
leaving CONFIG_RATIONAL=y unset.

Stripping out kunit.py, it's this:

$ echo -e 'CONFIG_KUNIT=y\nCONFIG_RATIONAL=y' > .kunit/.config
$ make ARCH=um olddefconfig O=.kunit
$ grep RATIONAL .kunit/.config

I'm not versed in Kconfig enough to know why CONFIG_RATIONAL=y is
getting removed.

>
> > is necessary
> > +       default KUNIT_ALL_TESTS
> > +       help
> > +               This builds unit tests for the rational number support.
> > +
> > +               If unsure, say N.
>
>
> --
> ~Randy
>