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

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Date:   Wed, 8 Sep 2021 14:16:28 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Nathan Chancellor <nathan@...nel.org>,
        Arnd Bergmann <arnd@...nel.org>
Cc:     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@...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@...glegroups.com
Subject: Re: [PATCH] Enable '-Werror' by default for all kernel builds

On 9/8/21 1:55 PM, Nathan Chancellor wrote:
> Hi Arnd,
> 
> 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@...nel.org> wrote:
>>>
>>> arm32-allmodconfig.log: crypto/wp512.c:782:13: error: stack frame size (1176) exceeds limit (1024) in function 'wp512_process_buffer' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/firmware/tegra/bpmp-debugfs.c:294:12: error: stack frame size (1256) exceeds limit (1024) in function 'bpmp_debug_show' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/firmware/tegra/bpmp-debugfs.c:357:16: error: stack frame size (1264) exceeds limit (1024) in function 'bpmp_debug_store' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c:3043:6: error: stack frame size (1384) exceeds limit (1024) in function 'bw_calcs' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dce_calcs.c:77:13: error: stack frame size (5560) exceeds limit (1024) in function 'calculate_bandwidth' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/mtd/chips/cfi_cmdset_0001.c:1872:12: error: stack frame size (1064) exceeds limit (1024) in function 'cfi_intelext_writev' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/ntb/hw/idt/ntb_hw_idt.c:1041:27: error: stack frame size (1032) exceeds limit (1024) in function 'idt_scan_mws' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/staging/fbtft/fbtft-core.c:902:12: error: stack frame size (1072) exceeds limit (1024) in function 'fbtft_init_display_from_property' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/staging/fbtft/fbtft-core.c:992:5: error: stack frame size (1064) exceeds limit (1024) in function 'fbtft_init_display' [-Werror,-Wframe-larger-than]
>>> arm32-allmodconfig.log: drivers/staging/rtl8723bs/core/rtw_security.c:1288:5: error: stack frame size (1040) exceeds limit (1024) in 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.
> 

Would it make sense to make KASAN depend on !COMPILE_TEST ?
After all, the point of KASAN is runtime testing, not build testing.

Guenter