Further exploration running slackware64-current
I tried different window managers using xwmconfig and startx to get a GUI window
These are the results:
xorg-server: = 1.19.6 ........ 1.20.0
xfce4 ......... OK ............ crashes X
fluxbox ....... OK ............ OK
blackbox ...... OK ............ OK
xfwm2 ......... OK ............ OK
wmaker ........ OK ............ OK
twm ........... OK ............ OK
kde4 .......... not installed / not installed
traceback from startx: (the warnings from xfce4-session are a red herring - they occur in
1.19.6 also, but it runs normally)
xauth: file /root/.serverauth.10487 does not exist
X.Org X Server 1.20.0
X Protocol Version 11, Revision 0
Build Operating System: Slackware 15.0 Slackware Linux Project
Current Operating System: Linux core5.localdomain 4.14.40 #2 SMP Wed May 9 15:56:50 CDT 2018 x86_64
Kernel command line: BOOT_IMAGE=Linux-ssd-m ro root=811 vt.default_utf8=1 acpi_enforce_resources=lax
Build Date: 10 May 2018 01:09:13PM
Current version of pixman: 0.34.0
Before reporting problems, check
http://wiki.x.org
to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.2.log", Time: Sun May 13 14:00:19 2018
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
resize called 1920 1080
/usr/bin/startxfce4: X server already running on display :2
gpg-agent[10531]: WARNING: "--write-env-file" is an obsolete option - it has no effect
gpg-agent: a gpg-agent is already running - not starting a new one
(xfce4-session:10525): xfce4-session-WARNING **: 14:00:19.723: gpg-agent returned no PID in the variables
(xfce4-session:10525): xfce4-session-WARNING **: 14:00:19.725: xfsm_manager_load_session: Something wrong with /root/.cache/sessions/xfce4-session-core5.localdomain:2, Does it exist? Permissions issue?
(EE)
(EE) Backtrace:
(EE) 0: /usr/libexec/Xorg (OsLookupColor+0x139) [0x58a319]
(EE) 1: /lib64/libpthread.so.0 (funlockfile+0x50) [0x7f91d23083cf]
(EE) 2: /usr/libexec/Xorg (miRenderColorToPixel+0xe) [0x4fef4e]
(EE) 3: /usr/lib64/xorg/modules/libexa.so (exaEnableDisableFBAccess+0x1fa6) [0x7f91cdc6f3e6]
(EE) 4: /usr/libexec/Xorg (DamageRegionAppend+0x676) [0x511406]
(EE) 5: /usr/libexec/Xorg (AddTraps+0x36d5) [0x5095d5]
(EE) 6: /usr/libexec/Xorg (SendErrorToClient+0x348) [0x43fa48]
(EE) 7: /usr/libexec/Xorg (InitFonts+0x3b8) [0x443928]
(EE) 8: /lib64/libc.so.6 (__libc_start_main+0xe7) [0x7f91d1f2dba7]
(EE) 9: /usr/libexec/Xorg (_start+0x2a) [0x42e5ba]
(EE)
(EE) Segmentation fault at address 0x8
(EE)
Fatal server error:
(EE) Caught signal 11 (Segmentation fault). Server aborting
(EE)
(EE)
Please consult the The X.Org Foundation support
at
http://wiki.x.org
for help.
(EE) Please also check the log file at "/var/log/Xorg.2.log" for additional information.
(EE)
(II) AIGLX: Suspending AIGLX clients for VT switch
(EE) Server terminated with error (1). Closing log file.
... messages from unhappy X clients deleted ....
So the segfault is in the server, probably unrelated to the particular video driver, but is triggered by calls made from the xfce4-session client.
Sorry I couldn't try kde4, but I'll bet it works, and nobody tested xfce4 before posting the upgrade...