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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH] Enable '-Werror' by default for all kernel builds
To:     =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Christoph Hellwig <hch@infradead.org>,
        Marco Elver <elver@google.com>
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From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <80a56a5a-5351-1897-b87e-3c3cd84bb13c@roeck-us.net>
Date:   Thu, 9 Sep 2021 07:59:56 -0700
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On 9/9/21 12:30 AM, Christian König wrote:
> 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.
> 

That specific warning is surrounded with "#ifndef CONFIG_COMPILE_TEST"
so it doesn't really matter because it doesn't cause test build failures.
Of course, we could do the same for any #warning which does now
cause a test build failure.

Guenter