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

On Wed, Sep 8, 2021 at 10:55 PM Nathan Chancellor [off-list ref] wrote:

On Tue, Sep 07, 2021 at 11:11:17AM +0200, Arnd Bergmann wrote:

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On Tue, Sep 7, 2021 at 4:32 AM Nathan Chancellor [off-list ref] wrote:

function 'rtw_aes_decrypt' [-Werror,-Wframe-larger-than]

quoted

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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/ (local)

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