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

From: "Christian König" <christian.koenig@amd.com>
To: Guenter Roeck <linux@roeck-us.net>,
	Christoph Hellwig <hch@infradead.org>,
	Marco Elver <elver@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Arnd Bergmann <arnd@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	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@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@googlegroups.com, "Pan, Xinhui" <Xinhui.Pan@amd.com>,
	amd-gfx@lists.freedesktop.org
Subject: Re: [PATCH] Enable '-Werror' by default for all kernel builds
Date: Thu, 9 Sep 2021 09:30:27 +0200	[thread overview]
Message-ID: <78aeab09-de88-966f-9f03-a2d56a0a6064@amd.com> (raw)
In-Reply-To: <a04c4c37-7151-ef7e-09ce-a61ac7b12106@roeck-us.net>

Am 09.09.21 um 08:07 schrieb Guenter Roeck:
> On 9/8/21 10:58 PM, Christoph Hellwig 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.
>>
>> While we're at it, with -Werror something like this is really futile:
>>
>> drivers/gpu/drm/amd/amdgpu/amdgpu_object.c: In function 
>> ‘amdgpu_bo_support_uswc’:
>> drivers/gpu/drm/amd/amdgpu/amdgpu_object.c:493:2: warning: #warning
>> Please enable CONFIG_MTRR and CONFIG_X86_PAT for better performance 
>> thanks to write-combining [-Wcpp
>>    493 | #warning Please enable CONFIG_MTRR and CONFIG_X86_PAT for 
>> better performance \
>>        |  ^~~~~~~

Ah, yes good point!

>
> I have been wondering if all those #warning "errors" should either
> be removed or be replaced with "#pragma message".

Well we started to add those warnings because people compiled their 
kernel with CONFIG_MTRR and CONFIG_X86_PAT and was then wondering why 
the performance of the display driver was so crappy.

When those warning now generate an error which you have to disable 
explicitly then that might not be bad at all.

It at least points people to this setting and makes it really clear that 
they are doing something very unusual and need to keep in mind that it 
might not have the desired result.

Regards,
Christian.

>
> Guenter