GCC LTO breaks color management in Plasma 6.3.0

[Vlad Zahorodnii]

On 2/13/25 2:04 PM, Neal Gompa wrote:
> On Thu, Feb 13, 2025 at 7:01 AM Vlad Zahorodnii<vlad.zahorodnii at kde.org> wrote:
>> Hello,
>>
>> We've received a number of complaints from Plasma Wayland users about
>> screen turning black when using an ICC profile (which contains a BToA
>> tag) and the new "Prefer color accuracy" setting. [1]
>>
>> The issue is reproducible only when kwin is built with GCC + LTO. If
>> kwin is built in the debug mode or the release mode but without LTO, the
>> issue is not reproducible. The issue is also not reproducible when using
>> clang + LTO.
>>
>> It might be worth to disable LTO when building kwin 6.3.0.
>>
>> Regards,
>> Vlad
>>
>> [1]https://bugs.kde.org/show_bug.cgi?id=499789
>>
> Is there a corresponding upstream GCC bug report about this? Also, the

Hi,

No, there is no upstream bug report yet. We would appreciate some help 
with communicating this issue upstream.

> linked bug report doesn't mention anything about LTO. How did we
> determine LTO is the cause?

We determined it by meticulously going through various combinations of 
build options, compilers, and linkers. We were able to reproduce the 
issue only when running kwin shipped by Arch, Fedora, and Neon. With dev 
builds, we are unable to reproduce the issue (unless LTO is enabled).

Regards,
Vlad
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