Xterm begins to handle expose events before it finishes to initialize itself.

$ gdb xterm
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This GDB was configured as "x86_64-redhat-linux-gnu"...
Using host libthread_db library "/lib64/libthread_db.so.1".
(gdb) break VTRun
Breakpoint 1 at 0x414190: file ./charproc.c, line 4787.
(gdb) r
Starting program: /usr/bin/xterm 

Program received signal SIGSEGV, Segmentation fault.
0x0000000000430d07 in handle_translated_exposure (xw=0x681c30, rect_x=0,
rect_y=0, rect_width=499, rect_height=316) at ./util.c:1684
1684	    leftcol = x0 / CurFontWidth(screen, screen->cur_row);
Missing separate debuginfos, use: debuginfo-install expat.x86_64 libXau.x86_64
libXcursor.x86_64 libXdmcp.x86_64 libXfixes.x86_64 libXpm.x86_64 libxcb.x86_64
(gdb) bt
#0  0x0000000000430d07 in handle_translated_exposure (xw=0x681c30, rect_x=0,
rect_y=0, rect_width=499, rect_height=316) at ./util.c:1684
#1  0x0000000000423d34 in Redraw () at ./misc.c:1258
#2  0x000000000042ce27 in ScrollBarOn (xw=0x681c30, init=<value optimized out>,
doalloc=1) at ./scrollbar.c:495
#3  0x0000000000415f6a in VTRealize (w=0x681c30, valuemask=0x7fffc341c2d8,
values=0x7fffc341c240) at ./charproc.c:6348
#4  0x0000003e21829166 in RealizeWidget (widget=0x681c30) at Intrinsic.c:306
#5  0x0000003e218292ae in RealizeWidget (widget=0x672790) at Intrinsic.c:355
#6  0x0000003e21829550 in XtRealizeWidget (widget=<value optimized out>) at
Intrinsic.c:385
#7  0x000000000040eb2b in VTInit () at ./charproc.c:5007
#8  0x000000000041dea3 in spawnXTerm (xw=0x681c30) at ./main.c:3227
#9  0x000000000041fb8f in main (argc=0, argv=<value optimized out>) at ./main.c:2274
#10 0x0000003e0c81e074 in __libc_start_main (main=0x41f340 <main>, argc=1,
ubp_av=0x7fffc341d8c8, init=<value optimized out>, fini=<value optimized out>,
rtld_fini=<value optimized out>, 
    stack_end=0x7fffc341d8b8) at libc-start.c:220
#11 0x0000000000406a39 in _start ()
(gdb) print screen->visbuf
$1 = (ScrnBuf) 0x16000
(gdb) print screen->allbuf
$2 = (ScrnBuf) 0x0
(gdb)

handle_translated_exposure() fires before VTRun() has a chance to call to
VTallocbuf() and allocate memory for terminal buffer.