This is a reproducible crash. I have loaded a lot of experimental lisp code, including some which creates a custom header line. It seems to be this that causes the crash, however only in combination with some buggy stuff that causes new frames to be used where a window split would do quite well. Without my window splitting bugs, I still get crashes but they are random and infrequent and I have been unable to create a reproducible test case. I am attaching a tgz of all the files involved, and embedding a gdb backtrace below. To reproduce: $ emacs .emacs That's all. Thanks. __ Marc ----------------gdb session showing backtrace--------------------- marc:~$ gdb /usr/local/bin/emacs --pid 3820 GNU gdb (Debian 7.12-6) 7.12.0.20161007-git Copyright (C) 2016 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: . Find the GDB manual and other documentation resources online at: . For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from /usr/local/bin/emacs...done. Attaching to program: /usr/local/bin/emacs, process 3820 [New LWP 3821] [New LWP 3822] [New LWP 3823] [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux- gnu/libthread_db.so.1". 0x00007f0cb10194cc in __pselect (nfds=13, readfds=0x7ffe74b635c0, writefds=0x7ffe74b63540, exceptfds=0x0, timeout=, sigmask=) at ../sysdeps/unix/sysv/linux/pselect.c:69 69 ../sysdeps/unix/sysv/linux/pselect.c: No such file or directory. (gdb) c Continuing. buffer.h:914: Emacs fatal error: assertion failed: BUFFERP (a) Fatal error 6: Aborted Backtrace: emacs[0x5af2a5] emacs[0x582c24] emacs[0x61849e] emacs[0x5802b3] emacs[0x468bb3] emacs[0x468ffd] emacs[0x4bbe06] emacs[0x63e3d7] emacs[0x638d1c] emacs[0x640ae0] emacs[0x63fc47] emacs[0x63f42b] emacs[0x64d106] emacs[0x64d5d6] emacs[0x63e406] emacs[0x638d1c] emacs[0x640ae0] emacs[0x640392] emacs[0x63e7d6] emacs[0x638d1c] emacs[0x640ae0] emacs[0x63fc47] emacs[0x63f3f8] emacs[0x58969d] emacs[0x63c004] emacs[0x589aa0] emacs[0x63f2b4] emacs[0x589b0c] emacs[0x587b2a] emacs[0x63bd55] emacs[0x58765b] emacs[0x63b285] emacs[0x587589] emacs[0x586b7b] emacs[0x5d02ab] emacs[0x5d0f00] emacs[0x640149] emacs[0x63fb06] emacs[0x68fb93] emacs[0x640710] emacs[0x63fb4a] emacs[0x5d29fc] emacs[0x6401b7] emacs[0x63fb06] emacs[0x63ed5e] emacs[0x63e219] emacs[0x638d1c] emacs[0x640ae0] emacs[0x63fc47] emacs[0x63ed5e] emacs[0x63febc] emacs[0x63fb06] emacs[0x68fb93] emacs[0x640710] emacs[0x63fb4a] emacs[0x68fb93] emacs[0x640710] emacs[0x63fb4a] emacs[0x68fb93] emacs[0x68edcc] emacs[0x63e439] emacs[0x63d993] emacs[0x635b30] emacs[0x640022] emacs[0x63fb06] emacs[0x68fb93] emacs[0x640710] emacs[0x63fb4a] emacs[0x63f42b] emacs[0x58824a] emacs[0x63bd55] emacs[0x58765b] emacs[0x63b285] emacs[0x5875f9] emacs[0x586b7b] emacs[0x586d6d] emacs[0x58494b] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f0cb0f582b1] emacs[0x41777a] Thread 1 "emacs" received signal SIGABRT, Aborted. raise (sig=6) at ../sysdeps/unix/sysv/linux/raise.c:51 51 ../sysdeps/unix/sysv/linux/raise.c: No such file or directory. (gdb) bt full #0 0x00007f0cb1a09f9f in raise (sig=6) at ../sysdeps/unix/sysv/linux/raise.c:51 set = {__val = {402653184, 0, 0, 0, 0, 0, 280375465082880, 71776119061217280, 7311138192406574195, 7074363581918293363, 8031173095775809139, 7596496585268228909, 0, 0, 32880, 139692512411867}} pid = tid = #1 0x0000000000582c67 in terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:399 #2 0x000000000061849e in die (msg=0x743f3f "BUFFERP (a)", file=0x743f36 "buffer.h", line=914) at alloc.c:7406 #3 0x00000000005802b3 in XBUFFER (a=0) at buffer.h:914 #4 0x0000000000468bb3 in mark_window_display_accurate_1 (w=0x558e410, accurate_p=false) at xdisp.c:14754 b = 0x7ffe74b60e40 #5 0x0000000000468ffd in mark_window_display_accurate (window=89711637, accurate_p=false) at xdisp.c:14811 w = 0x558e410 #6 0x00000000004bbe06 in Fforce_window_update (object=89711637) at window.c:3643 w = 0x558e410 #7 0x000000000063e3d7 in eval_sub (form=60546803) at eval.c:2241 i = 1 maxargs = 1 args_left = 0 numargs = 6 fun = 10198117 val = 140730856509392 original_fun = 715280 original_args = 60546787 funcar = 140730856509344 count = 47 argvals = {89711637, 47, 16360, 0, 0, 140730856509056, 3, 0} #8 0x0000000000638d1c in Fprogn (body=0) at eval.c:459 form = 60546803 val = 0 #9 0x0000000000640ae0 in funcall_lambda (fun=60544963, nargs=1, arg_vector=0x7ffe74b61118) at eval.c:3052 val = 32880 syms_left = 0 next = 55584 lexenv = 0 count = 46 i = 1 optional = false rest = false previous_optional_or_rest = false #10 0x000000000063fc47 in Ffuncall (nargs=2, args=0x7ffe74b61110) at eval.c:2790 fun = 60544963 original_fun = 60544963 funcar = 32880 numargs = 1 val = 49344 count = 45 #11 0x000000000063f42b in call1 (fn=60544963, arg1=89711637) at eval.c:2627 #12 0x000000000064d106 in mapcar1 (leni=2, vals=0x0, fn=60544963, seq=116876403) at fns.c:2486 tail = 117742163 dummy = 49344 i = 1 #13 0x000000000064d5d6 in Fmapc (function=60544963, sequence=116876403) at fns.c:2555 leni = 2 #14 0x000000000063e406 in eval_sub (form=60544883) at eval.c:2244 i = 2 maxargs = 2 args_left = 0 numargs = 10 fun = 14071717 val = 140730856510176 original_fun = 555488 original_args = 60544867 ---Type to continue, or q to quit--- funcar = 5755230 count = 44 argvals = {60544963, 116876403, 5757352, 60544387, 140730856510256, 6547512, 140730856510016, 19325507} #15 0x0000000000638d1c in Fprogn (body=60546483) at eval.c:459 form = 60544883 val = 59085860 #16 0x0000000000640ae0 in funcall_lambda (fun=60544835, nargs=0, arg_vector=0x7ffe74b613b0) at eval.c:3052 val = 2 syms_left = 0 next = 0 lexenv = 0 count = 44 i = 0 optional = false rest = false previous_optional_or_rest = false #17 0x0000000000640392 in apply_lambda (fun=60544835, args=0, count=43) at eval.c:2913 args_left = 0 i = 0 numargs = 0 arg_vector = 0x7ffe74b613b0 tem = 140730856510512 sa_avail = 16384 sa_count = 44 sa_must_free = false #18 0x000000000063e7d6 in eval_sub (form=60544323) at eval.c:2316 fun = 60544835 val = 0 original_fun = 45016704 original_args = 0 funcar = 32880 count = 43 argvals = {62107717, 0, 0, 0, 0, 0, 140730856510000, 140730856510000} #19 0x0000000000638d1c in Fprogn (body=0) at eval.c:459 form = 60544323 val = 0 #20 0x0000000000640ae0 in funcall_lambda (fun=60543331, nargs=0, arg_vector=0x7ffe74b61690) at eval.c:3052 val = 32880 syms_left = 0 next = 140730856512128 lexenv = 0 count = 43 i = 0 optional = false rest = false previous_optional_or_rest = false #21 0x000000000063fc47 in Ffuncall (nargs=1, args=0x7ffe74b61688) at eval.c:2790 fun = 60543331 original_fun = 45016752 funcar = 32880 numargs = 0 val = 140730856511104 count = 42 #22 0x000000000063f3f8 in call0 (fn=45016752) at eval.c:2619 #23 0x000000000058969d in safe_run_hooks_1 (nargs=2, args=0x7ffe74b61730) at keyboard.c:1792 #24 0x000000000063c004 in internal_condition_case_n (bfun=0x589650 , nargs=2, args=0x7ffe74b61730, handlers=49344, hfun= 0x58969f ) at eval.c:1416 val = 0 c = 0x386a830 #25 0x0000000000589aa0 in safe_run_hook_funcall (nargs=2, args=0x7ffe74b617c0) at keyboard.c:1840 #26 0x000000000063f2b4 in run_hook_with_args (nargs=2, args=0x7ffe74b617c0, funcall=0x589a20 ) at eval.c:2584 global_vals = 0 sym = 42048 ---Type to continue, or q to quit--- val = 89262371 ret = 0 #27 0x0000000000589b0c in safe_run_hooks (hook=42048) at keyboard.c:1856 count = 41 #28 0x0000000000587b2a in command_loop_1 () at keyboard.c:1280 prev_modiff = 0 prev_buffer = 0x0 already_adjusted = false #29 0x000000000063bd55 in internal_condition_case (bfun=0x587a37 , handlers=21120, hfun=0x58708e ) at eval.c:1336 val = 14099072 c = 0x3514e30 #30 0x000000000058765b in command_loop_2 (ignore=0) at keyboard.c:1110 val = 0 #31 0x000000000063b285 in internal_catch (tag=21792, func=0x58762e , arg=0) at eval.c:1101 val = 140730856512080 c = 0x351a3b0 #32 0x0000000000587589 in command_loop () at keyboard.c:1081 val = 14682304 #33 0x0000000000586b7b in recursive_edit_1 () at keyboard.c:695 count = 39 val = 140730856512128 #34 0x00000000005d02ab in read_minibuf (map=19501747, initial=0, prompt=62735124, expflag=false, histvar=5335856, histpos=2, defalt=0, allow_props=false, inherit_input_method=false) at minibuf.c:685 val = 0 count = 30 mini_frame = 22932533 ambient_dir = 61850116 minibuffer = 62107717 input_method = 0 enable_multibyte = 0 pos = 0 histstring = 5752337 histval = 0 empty_minibuf = 15209477 dummy = 0 frame = 22932533 #35 0x00000000005d0f00 in Fread_from_minibuffer (prompt=62735124, initial_contents=0, keymap=19501747, read=0, hist=5335856, default_value=0, inherit_input_method=0) at minibuf.c:992 histvar = 5335856 histpos = 2 val = 25784485600 #36 0x0000000000640149 in funcall_subr (subr=0x9c06e0 , numargs=7, args=0x7ffe74b61db0) at eval.c:2871 internal_argbuf = {10225376, 140730856512680, 5755230, 42964302368, 10225381, 140730856512712, 10225376, 140730856512704} internal_args = 0x7ffe74b61db0 #37 0x000000000063fb06 in Ffuncall (nargs=8, args=0x7ffe74b61da8) at eval.c:2776 fun = 10225381 original_fun = 659680 funcar = 11006539 numargs = 7 val = 140730856512832 count = 29 #38 0x000000000068fb93 in exec_byte_code (bytestr=11006396, vector=11006429, maxdepth=74, args_template=8202, nargs=8, args=0x7ffe74b62308) at bytecode.c:630 op = 7 type = CATCHER targets = {0x692b7f , 0x692ba7 , 0x692ba9 , 0x692bab , 0x692bad , 0x692bad , 0x692c12 , 0x692c86 , 0x68f2ff , 0x68f301 , 0x68f303 , 0x68f305 , 0x68f307 , 0x68f307 , 0x68f30d , 0x68f2ce , 0x68f7ab , 0x68f7ad , 0x68f7af , 0x68f7b1 , 0x68f7b3 , 0x68f7b3 , 0x68f7e8 , 0x68f7b9 , 0x68faab , 0x68faad , 0x68faaf , 0x68fab1 , 0x68fab3 , 0x68fab3 , 0x68fa65 , 0x68fa7c , 0x68fb6---Type to continue, or q to quit--- 0 , 0x68fb62 , 0x68fb64 , 0x68fb66 , 0x68fb68 , 0x68fb68 , 0x68fb1a , 0x68fb31 , 0x68fc15 , 0x68fc17 , 0x68fc19 , 0x68fc1b , 0x68fc1d , 0x68fc1d , 0x68fbcf , 0x68fbe6 , 0x690487 , 0x69036a , 0x690361 , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x6906c4 , 0x6907dd , 0x690840 , 0x6908a4 , 0x69090c , 0x68f608 , 0x68f683 , 0x690986 , 0x68f54c , 0x68f6ee , 0x6909f1 , 0x690a5c , 0x690aa7 , 0x690b12 , 0x690b64 , 0x690c35 , 0x690c80 , 0x690ceb , 0x690d73 , 0x690dbe , 0x690e09 , 0x690e74 , 0x690edf , 0x690f4a , 0x690fd2 , 0x691024 , 0x691076 , 0x691147 , 0x6911bd , 0x691233 , 0x6913f5 , 0x691465 , 0x6914d5 , 0x691545 , 0x6915b5 , 0x691607 , 0x69167e , 0x6916d0 , 0x691722 , 0x691774 , 0x691883 , 0x6901db , 0x6918e1 , 0x69192c , 0x6919f8 , 0x691a61 , 0x691abf , 0x691b0a , 0x691b50 , 0x691b96 , 0x691be4 , 0x692b7f , 0x691c3f , 0x691c85 , 0x691ccb , 0x691d11 , 0x691d57 , 0x691d9d , 0x6901db , 0x692b7f , 0x691de8 , 0x691e3d , 0x691e88 , 0x691ed3 , 0x691f3e , 0x691fa9 , 0x691ff4 , 0x692129 , 0x692194 , 0x6921ff , 0x69226a , 0x6922b0 , 0x692b7f , 0x69010f , 0x68fccc , 0x68f4c0 , 0x68fd7f , 0x68fe00 , 0x68fe7e , 0x6900c3 , 0x6900d8 , 0x68fa12 , 0x690192 , 0x690212 , 0x6902a6 , 0x6902ef , 0x6904d3 , 0x690550 , 0x6905d8 , 0x69063e , 0x68fc7e , 0x6922fb , 0x692383 , 0x6923ce , 0x692419 , 0x692464 , 0x6924af , 0x69251a , 0x692585 , 0x6925f0 , 0x69265b , 0x6927d4 , 0x69283f , 0x6928aa , 0x6928f5 , 0x692960 , 0x6929cb , 0x692a16 , 0x692a61 , 0x6917c6 , 0x691818 , 0x692ab3 , 0x692b1b , 0x692b7f , 0x68fefc , 0x68ff19 , 0x68ff85 , 0x68fff1 , 0x69005a , 0x690bb6 , 0x6910c8 , 0x691979 , 0x692d19 , 0x692d8e , 0x692b7f , 0x692b7f , 0x692e24 , 0x692eab , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x6930b2 } const_length = 13 bytestr_length = 91 vectorp = 0xa7f1e0 quitcounter = 1 '\001' stack_items = 19 sa_avail = 16141 sa_count = 26 sa_must_free = false stack_base = 0x7ffe74b61d50 stack_lim = 0x7ffe74b61de8 top = 0x7ffe74b61da8 void_stack_lim = 0x7ffe74b61de8 bytestr_data = 0x7ffe74b61de8 "\003:\203\r" pc = 0x7ffe74b61e2a "\211˚\203Y" count = 26 result = 139692541216827 #39 0x0000000000640710 in funcall_lambda (fun=11006349, nargs=8, arg_vector=0x7ffe74b622c8) at eval.c:2977 size = 5 val = 0 syms_left = 8202 next = 6182 lexenv = 77324040736 count = 26 i = 5755230 optional = false rest = false previous_optional_or_rest = 127 #40 0x000000000063fb4a in Ffuncall (nargs=9, args=0x7ffe74b622c0) at eval.c:2778 ---Type to continue, or q to quit--- fun = 11006349 original_fun = 5312064 funcar = 24 numargs = 8 val = 140730856514176 count = 25 #41 0x00000000005d29fc in Fcompleting_read (prompt=62735124, collection=11037325, predicate=16224, require_match=49344, initial_input=0, hist=5335856, def=0, inherit_input_method=0) at minibuf.c:1698 #42 0x00000000006401b7 in funcall_subr (subr=0x9c08e0 , numargs=8, args=0x7ffe74b62438) at eval.c:2876 internal_argbuf = {10225888, 140730856514440, 5755230, 42964302368, 10225893, 140730856514472, 10225888, 140730856514464} internal_args = 0x7ffe74b62438 #43 0x000000000063fb06 in Ffuncall (nargs=9, args=0x7ffe74b62430) at eval.c:2776 fun = 10225893 original_fun = 10225893 funcar = 0 numargs = 8 val = 140730856514592 count = 24 #44 0x000000000063ed5e in Fapply (nargs=2, args=0x7ffe74b62520) at eval.c:2396 i = 9 numargs = 8 funcall_nargs = 9 funcall_args = 0x7ffe74b62430 spread_arg = 0 fun = 10225893 retval = 5755230 sa_avail = 16312 sa_count = 24 sa_must_free = false #45 0x000000000063e219 in eval_sub (form=21981923) at eval.c:2212 vals = 0x7ffe74b62520 argnum = 2 sa_avail = 16368 sa_count = 24 sa_must_free = false args_left = 0 numargs = 10 fun = 14065701 val = 0 original_fun = 10464 original_args = 21981907 funcar = 140730856515096 count = 23 argvals = {140730856515712, 120, 139692541310816, 0, 513, 4096, 140730856515712, 55831552} #46 0x0000000000638d1c in Fprogn (body=0) at eval.c:459 form = 21981923 val = 0 #47 0x0000000000640ae0 in funcall_lambda (fun=21687635, nargs=7, arg_vector=0x7ffe74b62788) at eval.c:3052 val = 32880 syms_left = 0 next = 41029888 lexenv = 0 count = 14 i = 7 optional = true rest = false previous_optional_or_rest = false #48 0x000000000063fc47 in Ffuncall (nargs=8, args=0x7ffe74b62780) at eval.c:2790 fun = 21687635 original_fun = 41029696 funcar = 32880 numargs = 7 val = 140730856515440 ---Type to continue, or q to quit--- count = 13 #49 0x000000000063ed5e in Fapply (nargs=3, args=0x7ffe74b62978) at eval.c:2396 i = 8 numargs = 7 funcall_nargs = 8 funcall_args = 0x7ffe74b62780 spread_arg = 0 fun = 21687635 retval = 140730856515696 sa_avail = 16320 sa_count = 13 sa_must_free = false #50 0x000000000063febc in funcall_subr (subr=0xd6a020 , numargs=3, args=0x7ffe74b62978) at eval.c:2831 #51 0x000000000063fb06 in Ffuncall (nargs=4, args=0x7ffe74b62970) at eval.c:2776 fun = 14065701 original_fun = 10464 funcar = 140730856515888 numargs = 3 val = 140730856517120 count = 12 #52 0x000000000068fb93 in exec_byte_code (bytestr=22467972, vector=23203765, maxdepth=22, args_template=514, nargs=6, args=0x7ffe74b62e00) at bytecode.c:630 op = 3 type = (unknown: 1958096304) targets = {0x692b7f , 0x692ba7 , 0x692ba9 , 0x692bab , 0x692bad , 0x692bad , 0x692c12 , 0x692c86 , 0x68f2ff , 0x68f301 , 0x68f303 , 0x68f305 , 0x68f307 , 0x68f307 , 0x68f30d , 0x68f2ce , 0x68f7ab , 0x68f7ad , 0x68f7af , 0x68f7b1 , 0x68f7b3 , 0x68f7b3 , 0x68f7e8 , 0x68f7b9 , 0x68faab , 0x68faad , 0x68faaf , 0x68fab1 , 0x68fab3 , 0x68fab3 , 0x68fa65 , 0x68fa7c , 0x68fb60 , 0x68fb62 , 0x68fb64 , 0x68fb66 , 0x68fb68 , 0x68fb68 , 0x68fb1a , 0x68fb31 , 0x68fc15 , 0x68fc17 , 0x68fc19 , 0x68fc1b , 0x68fc1d , 0x68fc1d , 0x68fbcf , 0x68fbe6 , 0x690487 , 0x69036a , 0x690361 , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x692b7f , 0x6906c4 , 0x6907dd , 0x690840 , 0x6908a4 , 0x69090c , 0x68f608 , 0x68f683 , 0x690986 , 0x68f54c , 0x68f6ee , 0x6909f1 , 0x690a5c , 0x690aa7 , 0x690b12 , 0x690b64 , 0x690c35 , 0x690c80 , 0x690ceb , 0x690d73 , 0x690dbe , 0x690e09 , 0x690e74 , 0x690edf , 0x690f4a , 0x690fd2 , 0x691024 , 0x691076 , 0x691147 , 0x6911bd , 0x691233 , 0x6913f5 , 0x691465 , 0x6914d5 , 0x691545 , 0x6915b5 , 0x691607 , 0x69167e , 0x6916d0 , 0x691722 , 0x691774 , 0x691883 , 0x6901db , 0x6918e1 , 0x69192c , 0x6919f8 , 0x691a61 , 0x691abf , 0x691b0a , 0x691b50 , 0x691b96 , 0x691be4 , 0x692b7f , 0x691c3f , 0x691c85 , 0x691ccb , 0x691d11 , 0x691d57 , 0x691d9d , 0x6901db , 0x692b7f , 0x691de8 , 0x691e3d , 0x691e88 , 0x691ed3 , 0x691f3e , 0x691fa9 , 0x691ff4 , 0x692129 , 0x692194 , 0x6921ff , 0x69226a , 0x6922b0 , 0x692b7f , 0x69010f , 0x68fccc , 0x68f4c0 , 0x68fd7f , 0x68fe00 , 0x68fe7e , 0x6900c3 , 0x6900d8 , 0x68fa12 , 0x690192 , 0x690212 , 0x6902a6 , 0x6902ef , 0x6904d3 , 0x690550 , 0x6905d8 , 0x69063e , 0x68fc7e , 0x6922fb , 0x692383 , 0x6923ce , 0x692419 , 0x692464 , 0x6924af , 0x69251a , 0x692585 , 0x6925f0 , 0x69265b , 0x6927d4 , 0x69283f , 0x6928aa , 0x6928f5 , 0x692960 , 0x6929cb , 0x692a16 , 0x692a61 , 0x6917c6 , 0x691818 , 0x692ab3 , 0x692b1b , 0x692b7f , 0x68fefc , 0x68ff19 , 0x68ff85 , 0x68fff1 , 0x69005a , 0x690bb6 to continue, or q to quit--- byte_code+7624>, 0x6910c8