I was using SKK. It seems I hit C-SPC when it crashed. I don't think I did something special. I cannot reproduce this. (gdb) set height 0 (gdb) bt #0 0x403e3911 in kill () from /lib/libc.so.6 #1 0x808f01d in fatal_error_signal (sig=11) at emacs.c:272 #2 0x403e3848 in sigaction () from /lib/libc.so.6 #3 0x808bc3f in mark_hash_table (obj=141090416) at elhash.c:212 #4 0x8054872 in mark_object (obj=141090416) at alloc.c:2519 #5 0x808bc4b in mark_hash_table (obj=137160128) at elhash.c:213 #6 0x8054872 in mark_object (obj=137160128) at alloc.c:2519