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

Arnd Bergmann
2021-09-21T15:42:17Z

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