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

From: Arnd Bergmann <arnd@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>,
	"Guenter Roeck" <linux@roeck-us.net>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	llvm@lists.linux.dev,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	"Andrey Ryabinin" <ryabinin.a.a@gmail.com>,
	"Alexander Potapenko" <glider@google.com>,
	"Dmitry Vyukov" <dvyukov@google.com>,
	"Andrey Konovalov" <andreyknvl@gmail.com>,
	kasan-dev <kasan-dev@googlegroups.com>,
	"Harry Wentland" <harry.wentland@amd.com>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Christian König" <christian.koenig@amd.com>,
	"xinhui pan" <Xinhui.Pan@amd.com>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>
Subject: Re: [PATCH] Enable '-Werror' by default for all kernel builds
Date: Tue, 21 Sep 2021 17:41:58 +0200	[thread overview]
Message-ID: <CAK8P3a0tswcc1icb99cmdX7w0nBc4CAXjaAKJMuYSdJC1MS8YQ@mail.gmail.com> (raw)
In-Reply-To: <YTkjJPCdR1VGaaVm@archlinux-ax161>

On Wed, Sep 8, 2021 at 10:55 PM Nathan Chancellor <nathan@kernel.org> wrote:
> On Tue, Sep 07, 2021 at 11:11:17AM +0200, Arnd Bergmann wrote:
> > On Tue, Sep 7, 2021 at 4:32 AM Nathan Chancellor <nathan@kernel.org> wrote:
function 'rtw_aes_decrypt' [-Werror,-Wframe-larger-than]
> > > arm32-fedora.log: drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c:3043:6: error: stack frame size (1376) exceeds limit (1024) in function 'bw_calcs' [-Werror,-Wframe-larger-than]
> > > arm32-fedora.log: drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c:77:13: error: stack frame size (5384) exceeds limit (1024) in function 'calculate_bandwidth' [-Werror,-Wframe-larger-than]
> > >
> > > Aside from the dce_calcs.c warnings, these do not seem too bad. I
> > > believe allmodconfig turns on UBSAN but it could also be aggressive
> > > inlining by clang. I intend to look at all -Wframe-large-than warnings
> > > closely later.
> >
> > I've had them close to zero in the past, but a couple of new ones came in.
> >
> > The amdgpu ones are probably not fixable unless they stop using 64-bit
> > floats in the kernel for
> > random calculations. The crypto/* ones tend to be compiler bugs, but hard to fix
>
> I have started taking a look at these. Most of the allmodconfig ones
> appear to be related to CONFIG_KASAN, which is now supported for
> CONFIG_ARM.
>
> The two in bpmp-debugfs.c appear regardless of CONFIG_KASAN and it turns
> out that you actually submitted a patch for these:
>
> https://lore.kernel.org/r/20201204193714.3134651-1-arnd@kernel.org/
>
> Is it worth resending or pinging that?

I'm now restarting from a clean tree for my randconfig patches to see which
ones are actually needed, will hopefully get to that.

> The dce_calcs.c ones also appear without CONFIG_KASAN, which you noted
> is probably unavoidable.

(adding amdgpu folks to Cc here)

Harry Wentland did a nice rework for dcn_calcs.c that should also be
portable to dce_calcs.c, I hope that he will be able to get to that as well.

Looking at my older patches now, I found that I had only suppressed that one
and given up fixing it, but I did put my analysis into
https://bugs.llvm.org/show_bug.cgi?id=42551, which should be helpful
for addressing it in either the kernel or the compiler.

        Arnd