linux-kernel - Re: [PATCH] Enable '-Werror' by default for all kernel builds

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Date:   Thu, 9 Sep 2021 13:00:25 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev, Nick Desaulniers <ndesaulniers@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>
Subject: Re: [PATCH] Enable '-Werror' by default for all kernel builds

On Thu, Sep 9, 2021 at 12:54 PM Marco Elver <elver@...gle.com> wrote:
> On Thu, 9 Sept 2021 at 07:59, Christoph Hellwig <hch@...radead.org> wrote:
> > On Wed, Sep 08, 2021 at 11:58:56PM +0200, Marco Elver wrote:
> > > It'd be good to avoid. It has helped uncover build issues with KASAN in
> > > the past. Or at least make it dependent on the problematic architecture.
> > > For example if arm is a problem, something like this:
> >
> > I'm also seeing quite a few stack size warnings with KASAN on x86_64
> > without COMPILT_TEST using gcc 10.2.1 from Debian.  In fact there are a
> > few warnings without KASAN, but with KASAN there are a lot more.
> > I'll try to find some time to dig into them.
>
> Right, this reminded me that we actually at least double the real
> stack size for KASAN builds, because it inherently requires more stack
> space. I think we need Wframe-larger-than to match that, otherwise
> we'll just keep having this problem:
>
> https://lkml.kernel.org/r/20210909104925.809674-1-elver@google.com

The problem with this is that it completely defeats the point of the
stack size warnings in allmodconfig kernels when they have KASAN
enabled and end up missing obvious code bugs in drivers that put
large structures on the stack. Let's not go there.

        Arnd