linux-kernel - Re: [PATCH] [RFC] kunit: move binary assertion out of line

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Date:   Mon, 13 Jan 2020 18:13:39 -0800
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] kunit: move binary assertion out of line

On Mon, Jan 13, 2020 at 6:12 PM Brendan Higgins
<brendanhiggins@...gle.com> wrote:
>
> On Fri, Jan 10, 2020 at 5:43 AM Arnd Bergmann <arnd@...db.de> wrote:
> >
> > In combination with the structleak gcc plugin, kunit can lead to excessive
> > stack usage when each assertion adds another structure to the stack from
> > of the calling function:
> >
> > base/test/property-entry-test.c:99:1: error: the frame size of 3032 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> >
> > As most assertions are binary, change those over to a direct function
> > call that does not have this problem.  This can probably be improved
> > further, I just went for a straightforward conversion, but a function
> > call with 12 fixed arguments plus varargs it not great either.
>
> Yeah, I am not exactly excited by maintaining such a set of functions.
>
> I don't think anyone wants to go with the heap allocation route.
>
> Along the lines of the union/single copy idea[1]. What if we just put
> a union of all the assertion types in the kunit struct? One is already
> allocated for every test case and we only need one assertion object
> for each test case at a time, so I imagine that sould work.
>
> I will start messing around with the idea. Still, it sounds like we
> are down to either reducing the number of instances of this struct
> that get created per test case, or we need to remove it entirely (as
> you have done here).
>
> Cheers

Woops forgot to link the original discussion.

[1] https://lkml.org/lkml/2020/1/13/1166