Bug#1125313: libc6: Performance regression in KDE/Qt apps after update to 2.41-12+deb13u1
Package: libc6
Version: 2.41-12+deb13u1
Severity: important
X-Debbugs-Cc: alexsc.debian@gmail.com
Dear Maintainer,
After upgrading to glibc 2.41-12+deb13u1 (Debian 13.3 point release on
January 10, 2026), all KDE/Qt applications experience severe startup
delays of 1-3 seconds. Previously these applications started instantly.
What led up to the situation:
System was updated with 'apt upgrade' which included the glibc update
from the 13.3 point release.
What exactly did you do:
Tested multiple terminals and applications:
- Konsole: 2-3 second startup delay
- Alacritty: 1-2 second startup delay
- Other Qt/KDE applications show similar slowdown
- Non-Qt applications (xterm) start instantly
What was the outcome:
All Qt/KDE applications now have significant startup delays making the
system feel sluggish and unresponsive.
What outcome did you expect:
Applications should start instantly as they did before the update.
Additional information:
- Tested on both kernel 6.12.57 and 6.12.63 - issue persists on both
- GLIBC_TUNABLES=glibc.rtld.execstack=1 workaround does NOT resolve the issue
- Intel Iris Xe Graphics (amd64), KDE Plasma on Wayland
- This represents a significant usability regression for a stable release
-- System Information:
Debian Release: 13.3
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)
Kernel: Linux 6.12.63+deb13-amd64 (SMP w/8 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled
Versions of packages libc6 depends on:
ii libgcc-s1 14.2.0-19
Versions of packages libc6 recommends:
ii libidn2-0 2.3.8-2
Versions of packages libc6 suggests:
ii debconf [debconf-2.0] 1.5.91
pn glibc-doc <none>
ii libc-l10n 2.41-12+deb13u1
pn libnss-nis <none>
pn libnss-nisplus <none>
ii locales 2.41-12+deb13u1
-- debconf information excluded
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