linux-kernel - Re: [PATCH] Documentation: kunit: update kconfig options needed for UML coverage

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Message-ID: <CAGS_qxp604tXbqzSg0nmz=Ws9ZzX47u-XCftNxfcamyM=GrQYw@mail.gmail.com>
Date:   Mon, 28 Mar 2022 13:58:06 -0500
From:   Daniel Latypov <dlatypov@...gle.com>
To:     Brendan Higgins <brendanhiggins@...gle.com>
Cc:     David Gow <davidgow@...gle.com>, Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Shuah Khan <skhan@...uxfoundation.org>, maxime@...no.tech
Subject: Re: [PATCH] Documentation: kunit: update kconfig options needed for
 UML coverage

On Mon, Mar 28, 2022 at 11:54 AM 'Brendan Higgins' via KUnit
Development <kunit-dev@...glegroups.com> wrote:
>
> On Mon, Mar 28, 2022 at 12:35 PM Daniel Latypov <dlatypov@...gle.com> wrote:
> >
> > On Fri, Mar 25, 2022 at 9:56 PM David Gow <davidgow@...gle.com> wrote:
> > >
> >
> > <snip>
> >
> > > >         # Append coverage options to the current config
> > > > -       $ echo -e "CONFIG_DEBUG_KERNEL=y\nCONFIG_DEBUG_INFO=y\nCONFIG_GCOV=y" >> .kunit/.kunitconfig
> > > > +       $ echo -e "CONFIG_DEBUG_KERNEL=y\nCONFIG_DEBUG_INFO=y\nCONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y\nCONFIG_GCOV=y" >> .kunit/.kunitconfig
> > > >         $ ./tools/testing/kunit/kunit.py run
> > >
> > > Would we want to instead use a chain of --kconfig_add arguments? (I
> > > think there are advantages either way...)
> >
> > I've been considering this ever since the --kconfig_add patch was accepted.
> > It's more compatible w/ commands using --kunitconfig, but it also
> > looks very verbose.
> > E.g. it looks like
> >
> > $ tools/testing/kunit/kunit.py run --make_options=CC=/usr/bin/gcc-6
> > --kconfig_add=CONFIG_DEBUG_INFO=y
> > --kconfig_add=CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> > --kconfig_add=CONFIG_GCOV=y
>
> I don't think it's *that* much more verbose, but I see your point. I
> personally prefer this, but not enough to argue about it.

I personally prefer it too, but I'm biased as the person who added
--kconfig_add.
They're both ugly enough I'd figured I'd save the bikeshedding for
another patch.

>
> > Neither looks very appealing to me, so I've just kept it as-is for now.
> >
> > Maybe there's something we can do to make this easier (e.g. allowing
> > --kunitconfig to be repeated and mergable)?
>
> I would like --kunitconfig to be repeadable and mergable.

Ack.
There's some things to consider first.

1. This will conflict w/
https://patchwork.kernel.org/project/linux-kselftest/patch/20220226212325.2984807-1-dlatypov@google.com/,
so I'm going to wait until that gets merged first.

2. some kconfigs can be incompatible (e.g. these options only work on
UML, can't combine w/ a non-UML compatible file)
How do we make this less of a footgun?
We'd talked about how it'd be nice if kconfig/"make olddefconfig"
could print out *why* options get dropped (either they're not visible,
have unmet deps, etc.). If we had that, I'd feel more comfortable w/
repeatable kunitconfig.

3. People have the ability to do this already if they're really sure it's safe
$ cat <files...> | ./tools/testing/kunit/kunit.py run --kunitconfig=/dev/stdin

4. are we committed to supporting a "uml_coverage.kunitconfig" file?
As shown by the existence of this patch, we've let it get broken for a
bit, at least against linux-next (afaik, it was working on
torvalds/master up until the 5.18 window opened and we had some
patches reworking CONFIG_DEBUG_INFO).

These instructions exist so others don't have to try and re-figure out
the steps/workarounds.
But they're not more formally "part of KUnit" since no one has had the
expertise to maintain it (and fix issues like the reliance on gcc-6),
etc.

Creating a kunitconfig file for this will further imply ownership.