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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 8 Sep 2021 15:27:52 -0700
Message-ID: <CAHk-=wiQoxwGkMF34k3twte0N2phNCjbxtsgoW9YNybVPXZtsA@mail.gmail.com>
Subject: Re: ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger
 than 1024 bytes [-Werror=frame-larger-than=]
To:     Brendan Higgins <brendanhiggins@google.com>
Cc:     Shuah Khan <skhan@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Ariel Elior <aelior@marvell.com>,
        GR-everest-linux-l2@marvell.com, Wei Liu <wei.liu@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        open list <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>, lkft-triage@lists.linaro.org,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        KUnit Development <kunit-dev@googlegroups.com>
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On Wed, Sep 8, 2021 at 2:25 PM Brendan Higgins
<brendanhiggins@google.com> wrote:
>
> I definitely agree that in the cases where KUnit is not actually
> contributing to blowing the stack - struct leak just thinks it is,
> this is fine; however, it sounds like Linus' concerns with KUnit's
> macros go deeper than this.

I don't mind Kunit tests when they don't cause problems, but one very
natural way to use the Kunit test infrastructure does seem to be to
just put a lot of them into one function.

And then the individually fairly small structures just add up.
Probably mainly in some special configurations (ie together with
CONFIG_KASAN_STACK as pointed out by Arnd, but there might be other
cases that cause that issue too) where the compiler then doesn't merge
stack slots.

I wonder if those 'kunit_assert' structures could be split into two:
one part that could be 'static const', and at least shrink the dynamic
stack use that way. Because at a minimun, things like
type/file/line/format-msg seem to be things that really are just
static and const.

Hmm?

          Linus