I have recently been involved in bug reports etc for a new problem in Fedora 40, where a recent update has effectively broken all QT applications, resulting in KDE not functioning, and even # make xconfig is broken.

The Fedora bug report is here:  https://bugzilla.redhat.com/show_bug.cgi?id=2272758

The problem is:

# kwrite
Illegal instruction (core dumped)
# kate
Illegal instruction (core dumped)
# make xconfig
make[2]: *** [scripts/kconfig/Makefile:56: xconfig] Illegal instruction (core dumped)
make[1]: *** [/usr/src/linux-6.8.2/Makefile:689: xconfig] Error 2
make: *** [Makefile:240: __sub-make] Error 2
and
# startplasma
Illegal instruction (core dumped)

The system then becomes very sluggish, as various coredump processes start to hog the CPU..

It seems that the actual problem is caused by a recent update to GCC 14, and the solution would have been to revert to an earlier version of the affected software (#dnf downgrade…), but these are no longer on the servers (as F40 is still in dev mode)..

Until a proper solution is available, I have found a ‘nasty hack’ that at least gets most things working properly…

The affected version of qt6-qtbase is 6.6.2, so I found ‘good’ versions as follows:
qt6-qtbase-6.6.2-1.el9.next.x86_64.rpm
which requires an earlier version of libicu, so:
libicu-67.1-9.el9.x86_64.rpm
Both of these have to be forcibly installed, not surprisingly, so:

# rpm -Uvh qt6-qtbase-6.6.2-1.el9.next.x86_64.rpm --nodeps --force

and

# rpm -ivh libicu-67.1-9.el9.x86_64.rpm --nodeps --force

After that, the affected applications work again, and I can get a Plasma desktop…

As I mentioned, this is a ‘nasty hack’ and should only be applied if you can’t wait for the ‘official’ fix to be available (which as of April 3rd has no date for availability…)

Robert Gadsdon.    April 3rd 2024.