The segfault happens in the child process that was forked by the forkSqueak prim. It occurs in the new epoll code. I don't yet see the cause (there is no obvious null pointer issue) but the gdb backtrace is:
(gdb) bt #0 0x0000000000dd39b0 in ?? () #1 0x00000000004d62dc in aioPoll (microSeconds=0) at /home/lewis/squeak/git/opensmalltalk-vm/platforms/unix/vm/aio.c:405 #2 0x00007fa016315e39 in display_ioProcessEvents () at /home/lewis/squeak/git/opensmalltalk-vm/platforms/unix/vm-display-X11/sqUnixX11.c:4867 #3 0x0000000000417ca3 in ioProcessEvents () at /home/lewis/squeak/git/opensmalltalk-vm/platforms/unix/vm/sqUnixMain.c:726 #4 0x0000000000441f58 in checkForEventsMayContextSwitch (mayContextSwitch=1) at /home/lewis/squeak/git/opensmalltalk-vm/spurstack64src/vm/gcc3x-interp.c:50306 #5 0x00000000004401ca in handleStackOverflowOrEventAllowContextSwitch (mayContextSwitch=1) at /home/lewis/squeak/git/opensmalltalk-vm/spurstack64src/vm/gcc3x-interp.c:53718 #6 0x0000000000426cbd in interpret () at /home/lewis/squeak/git/opensmalltalk-vm/spurstack64src/vm/gcc3x-interp.c:5844 #7 0x000000000043ab1f in enterSmalltalkExecutiveImplementation () at /home/lewis/squeak/git/opensmalltalk-vm/spurstack64src/vm/gcc3x-interp.c:51798 #8 0x000000000041d4ba in interpret () at /home/lewis/squeak/git/opensmalltalk-vm/spurstack64src/vm/gcc3x-interp.c:2493 #9 0x000000000041ad0a in main (argc=2, argv=0x7ffc3ba11f78, envp=0x7ffc3ba11f90) at /home/lewis/squeak/git/opensmalltalk-vm/platforms/unix/vm/sqUnixMain.c:2164