Public bug reported:
Title: plasmashell segfaults in FcCharSetHasChar (libfontconfig) via
QFontEngineMultiFontConfig during any QML text Label rendering at
startup — 100% reproducible
Affected packages: fontconfig 2.17.1-3ubuntu1, libfontconfig1
2.17.1-3ubuntu1, qt6-declarative 6.10.2+dfsg-3 (libqt6qml6), on Ubuntu
26.10 "resolute"
Summary:
plasmashell crashes with SIGSEGV on every launch, deterministically, in
FcCharSetHasChar() inside libfontconfig.so.1, called from
QFontEngineMultiFontConfig::shouldLoadFontEngineForCharacter() in Qt6Gui. The
crash occurs the moment any QQuickLabel/Text element completes layout during
Plasma's early startup — confirmed across multiple different trigger widgets
(Klipper's clipboard applet, and later the systray's own "plugin not found"
error notification label), indicating this is not specific to any one applet
but a general failure in fontconfig/Qt's font-matching path.
Steps already ruled out:
Not caused by clipboard history data (cleared, still crashes)
Not caused by missing/corrupt font files (fc-validate found no structural
issues)
Not caused by stale fontconfig cache (full rebuild via fc-cache -f -v — crash
returns after reboot)
Not caused by disk/hardware failure (extended SMART self-test on system drive
completed with zero errors)
Not caused by the specific applet (disabling Klipper's plugin file entirely —
libklipperplugin.so renamed — crash still occurs, now triggered by a different
Label instead)
Backtrace (key frames):
Thread 1 "plasmashell" received signal SIGSEGV, Segmentation fault.
#1 FcCharSetHasChar () from libfontconfig.so.1
#2 QFontEngineMultiFontConfig::shouldLoadFontEngineForCharacter(int, unsigned
int) const
#3 QFontEngineMulti::stringToCMap(...)
#4 QTextEngine::shapeText(int) const
#5 QTextLine::layout_helper(int)
#6 QQuickTextPrivate::setLineGeometry(...)
#9 QQuickTextPrivate::updateLayout()
#10 QQuickLabel::componentComplete()
Reproduction: Simply launch plasmashell --replace on a fresh session;
crashes within 1-2 seconds every time.
Suspected cause: Possible use-after-free or stale pointer in Qt's
QFontEngineMultiFontConfig cached FcPattern* handling, interacting with
fontconfig 2.17.1's internal charset/pattern lifetime — both are very
recent versions paired together for the first time in this Ubuntu
release.
ProblemType: Bug
DistroRelease: Ubuntu 26.04
Package: libqt6qml6 6.10.2+dfsg-3
ProcVersionSignature: Ubuntu 7.0.0-34.34-generic 7.0.14
Uname: Linux 7.0.0-34-generic x86_64
ApportVersion: 2.34.1-0ubuntu0.1
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: KDE
Date: Fri Sep 25 21:24:53 2026
InstallationDate: Installed on 2026-04-27 (152 days ago)
InstallationMedia: Kubuntu 26.04 "Resolute Raccoon" - Release amd64 (20260423)
SourcePackage: qt6-declarative
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: qt6-declarative (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug resolute wayland-session
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https://bugs.launchpad.net/bugs/2168591
Title:
plamsamhell crashes consistently after login
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