# This version crashes.
package require Tclsdl
set screen [sdl::surface -width 640 -height 480 -bpp 32]
vwait forever

# This version does not crash.
package require Tclsdl
package require Tk
set screen [sdl::surface -width 640 -height 480 -bpp 32]
vwait forever

# This version does not crash.
package require Tclsdl
set screen [sdl::surface -width 640 -height 480 -bpp 32]
catch {wm withdraw .}
vwait forever

# Here is an excerpt from the backtrace:

#0  0x00007ffff70b95d1 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007ffff7b86849 in Tcl_DStringAppend (dsPtr=0x7fffffffd7c0, bytes=0x0, 
    length=-1)
    at /home/ben/local/distfiles/tcl8.5.9/unix/../generic/tclUtil.c:1838
#2  0x00007ffff57690cd in Tclsdl_BackgroundEvalObjv (interp=0x618df0, objc=2, 
    objv=0x7fffffffd910, flags=0) at ./generic/bgeval.c:43
#3  0x00007ffff5767eca in BgEvalObjv (interp=0x618df0, objc=2, 
    objv=0x7fffffffd910) at ./generic/tclsdl.c:22
#4  0x00007ffff576812f in EventProc (eventPtr=0x6b43a0, flags=-3)
    at ./generic/tclsdl.c:60
#5  0x00007ffff7b57014 in Tcl_ServiceEvent (flags=-3)
    at /home/ben/local/distfiles/tcl8.5.9/unix/../generic/tclNotify.c:677
#6  0x00007ffff7b5748b in Tcl_DoOneEvent (flags=-3)
    at /home/ben/local/distfiles/tcl8.5.9/unix/../generic/tclNotify.c:980
#7  0x00007ffff7b0cf38 in Tcl_VwaitObjCmd (clientData=0x0, interp=0x618df0, 
    objc=2, objv=0x61d100)
    at /home/ben/local/distfiles/tcl8.5.9/unix/../generic/tclEvent.c:1349
#8  0x00007ffff7aaa75c in TclEvalObjvInternal (interp=0x618df0, objc=2, 
    objv=0x61d100, command=0x629b48 "vwait forever\n", length=14, flags=0)
    at /home/ben/local/distfiles/tcl8.5.9/unix/../generic/tclBasic.c:3689
...