Hi all,

I do not have a good repro for this yet, but I have been running into the following bug a few times a day in the last two days, after updating to the latest emacs-25; I didn't have this issue with a version from about a month ago:

> (gdb) run
> Starting program: /build/emacs/src/emacs 
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
> [New Thread 0x7fffe9d0d700 (LWP 3717)]
> [New Thread 0x7fffe3fff700 (LWP 3718)]
> [New Thread 0x7fffe37fe700 (LWP 3719)]
> lisp.h:1555: Emacs fatal error: assertion failed: 0 <= size
> Fatal error 6: Aborted
> lisp.h:1555: Emacs fatal error: assertion failed: 0 <= size
> 
> Program received signal SIGABRT, Aborted.
> 0x00007ffff130920b in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:37
> 37	../nptl/sysdeps/unix/sysv/linux/pt-raise.c: No such file or directory.
> (gdb) backtrace
> #0  0x00007ffff130920b in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/pt-raise.c:37
> #1  0x0000000000588b41 in terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:398
> #2  0x000000000061a40d in die (msg=0x73e9ab "0 <= size", file=0x73e850 "lisp.h", line=1555) at alloc.c:7036
> #3  0x0000000000583b8e in ASIZE (array=14489661) at lisp.h:1555
> #4  0x0000000000584aa6 in VECTORP (x=14489661) at lisp.h:2640
> #5  0x0000000000677e4d in check_obarray (obarray=14489661) at lread.c:3723
> #6  0x000000000067814f in intern_1 (str=0x74bf1a "auto-save-hook", len=14) at lread.c:3770
> #7  0x0000000000585ae1 in intern (str=0x74bf1a "auto-save-hook") at lisp.h:3843
> #8  0x00000000005e46f0 in Fdo_auto_save (no_message=44352, current_only=0) at fileio.c:5506
> #9  0x000000000058af1c in shut_down_emacs (sig=6, stuff=0) at emacs.c:2030
> #10 0x0000000000588af1 in terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:382
> #11 0x000000000061a40d in die (msg=0x73e9ab "0 <= size", file=0x73e850 "lisp.h", line=1555) at alloc.c:7036
> #12 0x0000000000583b8e in ASIZE (array=49306789) at lisp.h:1555
> #13 0x0000000000584aa6 in VECTORP (x=49306789) at lisp.h:2640
> #14 0x0000000000616b75 in compact_font_cache_entry (entry=18559459) at alloc.c:5349
> #15 0x0000000000616ee0 in compact_font_caches () at alloc.c:5412
> #16 0x0000000000617679 in garbage_collect_1 (end=0x7fffffff4ca8) at alloc.c:5587
> #17 0x0000000000617d2b in Fgarbage_collect () at alloc.c:5792
> #18 0x0000000000585c55 in maybe_gc () at lisp.h:4649
> #19 0x000000000063f3e9 in Ffuncall (nargs=4, args=0x7fffffff4dd8) at eval.c:2643
> #20 0x000000000068c604 in exec_byte_code (bytestr=10672364, vector=10672397, maxdepth=30, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #21 0x000000000064050d in funcall_lambda (fun=10672253, nargs=5, arg_vector=0xa2d90d <pure+503021>) at eval.c:2921
> #22 0x000000000063f9c0 in Ffuncall (nargs=6, args=0x7fffffff5338) at eval.c:2742
> #23 0x000000000068c604 in exec_byte_code (bytestr=10672644, vector=10672677, maxdepth=30, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #24 0x000000000064050d in funcall_lambda (fun=10672597, nargs=2, arg_vector=0xa2da25 <pure+503301>) at eval.c:2921
> #25 0x000000000063f9c0 in Ffuncall (nargs=3, args=0x7fffffff5898) at eval.c:2742
> #26 0x000000000068c604 in exec_byte_code (bytestr=10672836, vector=10672869, maxdepth=18, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #27 0x000000000064050d in funcall_lambda (fun=10672789, nargs=2, arg_vector=0xa2dae5 <pure+503493>) at eval.c:2921
> #28 0x000000000063f9c0 in Ffuncall (nargs=3, args=0x7fffffff5de8) at eval.c:2742
> #29 0x000000000068c604 in exec_byte_code (bytestr=10694580, vector=10694613, maxdepth=22, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #30 0x000000000064050d in funcall_lambda (fun=10694533, nargs=2, arg_vector=0xa32fd5 <pure+525237>) at eval.c:2921
> #31 0x000000000063f9c0 in Ffuncall (nargs=3, args=0x7fffffff6338) at eval.c:2742
> #32 0x000000000068c604 in exec_byte_code (bytestr=10701108, vector=10701141, maxdepth=26, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #33 0x000000000064050d in funcall_lambda (fun=10701045, nargs=2, arg_vector=0xa34955 <pure+531765>) at eval.c:2921
> #34 0x000000000063f9c0 in Ffuncall (nargs=3, args=0x7fffffff68b0) at eval.c:2742
> #35 0x000000000063f0d1 in call2 (fn=20304, arg1=46566453, arg2=0) at eval.c:2560
> #36 0x0000000000560724 in x_create_tip_frame (dpyinfo=0xe8fa00, parms=60874755, text=51799508) at xfns.c:5637
> #37 0x000000000056140e in Fx_show_tip (string=51799508, frame=20942149, parms=60877619, timeout=22, dx=22, dy=-38) at xfns.c:5883
> #38 0x000000000063f884 in Ffuncall (nargs=7, args=0x7fffffff6c98) at eval.c:2714
> #39 0x000000000068c604 in exec_byte_code (bytestr=30015060, vector=21201429, maxdepth=54, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #40 0x000000000064050d in funcall_lambda (fun=20717717, nargs=10, arg_vector=0x1438215) at eval.c:2921
> #41 0x000000000063f9c0 in Ffuncall (nargs=11, args=0x7fffffff7228) at eval.c:2742
> #42 0x000000000068c604 in exec_byte_code (bytestr=29716340, vector=20569765, maxdepth=46, args_template=0, nargs=0, args=0x0) at bytecode.c:880
> #43 0x000000000064050d in funcall_lambda (fun=20570117, nargs=5, arg_vector=0x139dea5) at eval.c:2921
> #44 0x000000000063fd95 in apply_lambda (fun=20570117, args=34388947, count=81) at eval.c:2794
> #45 0x000000000063e0a8 in eval_sub (form=34388995) at eval.c:2211
> #46 0x0000000000638c13 in Fif (args=34389027) at eval.c:383
> #47 0x000000000063da93 in eval_sub (form=34389059) at eval.c:2119
> #48 0x0000000000638e97 in Fprogn (body=34388243) at eval.c:426
> #49 0x000000000063abc6 in Flet (args=34389075) at eval.c:946
> #50 0x000000000063da93 in eval_sub (form=34390467) at eval.c:2119
> #51 0x0000000000638e97 in Fprogn (body=34388179) at eval.c:426
> #52 0x000000000064047c in funcall_lambda (fun=34387299, nargs=1, arg_vector=0x7fffffff7d98) at eval.c:2914
> #53 0x000000000063fac8 in Ffuncall (nargs=2, args=0x7fffffff7d90) at eval.c:2754
> #54 0x000000000063dd22 in eval_sub (form=34386051) at eval.c:2137
> #55 0x0000000000638e97 in Fprogn (body=34426323) at eval.c:426
> #56 0x000000000063da93 in eval_sub (form=34426307) at eval.c:2119
> #57 0x0000000000638c13 in Fif (args=34425955) at eval.c:383
> #58 0x000000000063da93 in eval_sub (form=34425939) at eval.c:2119
> #59 0x0000000000638e97 in Fprogn (body=34425923) at eval.c:426
> #60 0x000000000063abc6 in Flet (args=34425907) at eval.c:946
> #61 0x000000000063da93 in eval_sub (form=34425891) at eval.c:2119
> #62 0x0000000000638e97 in Fprogn (body=34425683) at eval.c:426
> #63 0x000000000063da93 in eval_sub (form=34425699) at eval.c:2119
> #64 0x0000000000638c13 in Fif (args=34425619) at eval.c:383
> #65 0x000000000063da93 in eval_sub (form=34425635) at eval.c:2119
> #66 0x0000000000638e97 in Fprogn (body=34425539) at eval.c:426
> #67 0x000000000064047c in funcall_lambda (fun=34425331, nargs=1, arg_vector=0x7fffffff8748) at eval.c:2914
> #68 0x000000000063fac8 in Ffuncall (nargs=2, args=0x7fffffff8740) at eval.c:2754
> #69 0x000000000063dd22 in eval_sub (form=34634115) at eval.c:2137
> #70 0x0000000000638e97 in Fprogn (body=34634515) at eval.c:426
> #71 0x000000000063da93 in eval_sub (form=34634531) at eval.c:2119
> #72 0x0000000000638c13 in Fif (args=34634563) at eval.c:383
> #73 0x000000000063da93 in eval_sub (form=34634579) at eval.c:2119
> #74 0x0000000000638e97 in Fprogn (body=34632707) at eval.c:426
> #75 0x000000000064047c in funcall_lambda (fun=34632803, nargs=1, arg_vector=0x7fffffff8ba0) at eval.c:2914
> #76 0x000000000063fd95 in apply_lambda (fun=34632819, args=34632563, count=62) at eval.c:2794
> #77 0x000000000063e2a6 in eval_sub (form=34632547) at eval.c:2241
> #78 0x0000000000638e97 in Fprogn (body=34631443) at eval.c:426
> #79 0x000000000063da93 in eval_sub (form=34631459) at eval.c:2119
> #80 0x0000000000638c13 in Fif (args=34629699) at eval.c:383
> #81 0x000000000063da93 in eval_sub (form=34629715) at eval.c:2119
> #82 0x0000000000638e97 in Fprogn (body=34629731) at eval.c:426
> #83 0x000000000063abc6 in Flet (args=34629747) at eval.c:946
> #84 0x000000000063da93 in eval_sub (form=34629763) at eval.c:2119
> #85 0x0000000000638e97 in Fprogn (body=34629907) at eval.c:426
> #86 0x000000000063da93 in eval_sub (form=34629891) at eval.c:2119
> #87 0x0000000000638c13 in Fif (args=34629939) at eval.c:383
> #88 0x000000000063da93 in eval_sub (form=34629923) at eval.c:2119
> #89 0x0000000000638e97 in Fprogn (body=34630003) at eval.c:426
> #90 0x000000000063da93 in eval_sub (form=34629971) at eval.c:2119
> #91 0x000000000063ba41 in internal_lisp_condition_case (var=19875456, bodyform=34629971, handlers=34631203) at eval.c:1280
> #92 0x000000000063b533 in Fcondition_case (args=34630099) at eval.c:1206
> #93 0x000000000063da93 in eval_sub (form=34630115) at eval.c:2119
> #94 0x0000000000638e97 in Fprogn (body=34630179) at eval.c:426
> #95 0x000000000064047c in funcall_lambda (fun=34630275, nargs=0, arg_vector=0x7fffffff9870) at eval.c:2914
> #96 0x000000000063fd95 in apply_lambda (fun=34630291, args=0, count=52) at eval.c:2794
> #97 0x000000000063e2a6 in eval_sub (form=34420275) at eval.c:2241
> #98 0x0000000000638e97 in Fprogn (body=34416291) at eval.c:426
> #99 0x000000000063da93 in eval_sub (form=34416307) at eval.c:2119
> #100 0x0000000000638c13 in Fif (args=34416339) at eval.c:383
> #101 0x000000000063da93 in eval_sub (form=34416355) at eval.c:2119
> #102 0x0000000000638e97 in Fprogn (body=34416579) at eval.c:426
> #103 0x0000000000638cc6 in Fif (args=34416467) at eval.c:384
> #104 0x000000000063da93 in eval_sub (form=34416451) at eval.c:2119
> #105 0x0000000000638e97 in Fprogn (body=34414595) at eval.c:426
> #106 0x000000000063abc6 in Flet (args=34414611) at eval.c:946
> #107 0x000000000063da93 in eval_sub (form=34414627) at eval.c:2119
> #108 0x0000000000638e97 in Fprogn (body=34414643) at eval.c:426
> #109 0x000000000063a5fa in FletX (args=34414659) at eval.c:882
> #110 0x000000000063da93 in eval_sub (form=34414675) at eval.c:2119
> #111 0x0000000000638e97 in Fprogn (body=34414739) at eval.c:426
> #112 0x000000000064047c in funcall_lambda (fun=34414835, nargs=1, arg_vector=0x7fffffffa280) at eval.c:2914
> #113 0x000000000063fd95 in apply_lambda (fun=34414851, args=34391843, count=43) at eval.c:2794
> #114 0x000000000063e2a6 in eval_sub (form=34391827) at eval.c:2241
> #115 0x0000000000638e97 in Fprogn (body=34422355) at eval.c:426
> #116 0x000000000063da93 in eval_sub (form=34422371) at eval.c:2119
> #117 0x0000000000638c13 in Fif (args=34422403) at eval.c:383
> #118 0x000000000063da93 in eval_sub (form=34422419) at eval.c:2119
> #119 0x0000000000638e97 in Fprogn (body=34422499) at eval.c:426
> #120 0x000000000063abc6 in Flet (args=34422515) at eval.c:946
> #121 0x000000000063da93 in eval_sub (form=34422531) at eval.c:2119
> #122 0x0000000000638e97 in Fprogn (body=34422563) at eval.c:426
> #123 0x0000000000638dd6 in Fcond (args=34422579) at eval.c:408
> #124 0x000000000063da93 in eval_sub (form=34422691) at eval.c:2119
> #125 0x0000000000638e97 in Fprogn (body=34422707) at eval.c:426
> #126 0x000000000063abc6 in Flet (args=34422723) at eval.c:946
> #127 0x000000000063da93 in eval_sub (form=34422739) at eval.c:2119
> #128 0x0000000000638e97 in Fprogn (body=34420771) at eval.c:426
> #129 0x000000000062953c in Fsave_current_buffer (args=34420755) at editfns.c:1027
> #130 0x000000000063da93 in eval_sub (form=34420739) at eval.c:2119
> #131 0x0000000000638e97 in Fprogn (body=34420803) at eval.c:426
> #132 0x000000000063da93 in eval_sub (form=34420787) at eval.c:2119
> #133 0x0000000000638c13 in Fif (args=34420835) at eval.c:383
> #134 0x000000000063da93 in eval_sub (form=34420819) at eval.c:2119
> #135 0x0000000000638e97 in Fprogn (body=34420867) at eval.c:426
> #136 0x000000000063abc6 in Flet (args=34420883) at eval.c:946
> #137 0x000000000063da93 in eval_sub (form=34420899) at eval.c:2119
> #138 0x0000000000638e97 in Fprogn (body=34420963) at eval.c:426
> #139 0x000000000064047c in funcall_lambda (fun=34421059, nargs=3, arg_vector=0x7fffffffb3a8) at eval.c:2914
> #140 0x000000000063fac8 in Ffuncall (nargs=4, args=0x7fffffffb3a0) at eval.c:2754
> #141 0x000000000063e9d9 in Fapply (nargs=3, args=0x7fffffffb470) at eval.c:2321
> #142 0x000000000063dd22 in eval_sub (form=34395395) at eval.c:2137
> #143 0x0000000000638e97 in Fprogn (body=34395843) at eval.c:426
> #144 0x000000000064047c in funcall_lambda (fun=60093955, nargs=2, arg_vector=0x7fffffffb738) at eval.c:2914
> #145 0x000000000063fac8 in Ffuncall (nargs=3, args=0x7fffffffb730) at eval.c:2754
> #146 0x000000000063dd22 in eval_sub (form=34252099) at eval.c:2137
> #147 0x0000000000638e97 in Fprogn (body=34251907) at eval.c:426
> #148 0x000000000063abc6 in Flet (args=34251891) at eval.c:946
> #149 0x000000000063da93 in eval_sub (form=34251811) at eval.c:2119
> #150 0x0000000000638e97 in Fprogn (body=34251683) at eval.c:426
> #151 0x000000000064047c in funcall_lambda (fun=34251267, nargs=5, arg_vector=0x7fffffffbb20) at eval.c:2914
> #152 0x000000000063fd95 in apply_lambda (fun=34251251, args=34230211, count=21) at eval.c:2794
> #153 0x000000000063e2a6 in eval_sub (form=34230419) at eval.c:2241
> #154 0x0000000000638e97 in Fprogn (body=34230067) at eval.c:426
> #155 0x000000000063abc6 in Flet (args=34226755) at eval.c:946
> #156 0x000000000063da93 in eval_sub (form=34226739) at eval.c:2119
> #157 0x0000000000638e97 in Fprogn (body=34225411) at eval.c:426
> #158 0x0000000000638dd6 in Fcond (args=34225347) at eval.c:408
> #159 0x000000000063da93 in eval_sub (form=34225315) at eval.c:2119
> #160 0x0000000000638e97 in Fprogn (body=34225251) at eval.c:426
> #161 0x000000000063a5fa in FletX (args=34225235) at eval.c:882
> #162 0x000000000063da93 in eval_sub (form=34225219) at eval.c:2119
> #163 0x000000000063ba41 in internal_lisp_condition_case (var=8523776, bodyform=34225219, handlers=34229795) at eval.c:1280
> #164 0x000000000063b533 in Fcondition_case (args=34224435) at eval.c:1206
> #165 0x000000000063da93 in eval_sub (form=34224419) at eval.c:2119
> #166 0x0000000000638e97 in Fprogn (body=34224355) at eval.c:426
> #167 0x000000000062953c in Fsave_current_buffer (args=34224371) at editfns.c:1027
> #168 0x000000000063da93 in eval_sub (form=34224403) at eval.c:2119
> #169 0x0000000000638e97 in Fprogn (body=34224307) at eval.c:426
> #170 0x000000000063da93 in eval_sub (form=34224323) at eval.c:2119
> #171 0x0000000000638c13 in Fif (args=34224259) at eval.c:383
> #172 0x000000000063da93 in eval_sub (form=34224275) at eval.c:2119
> #173 0x0000000000638e97 in Fprogn (body=34224051) at eval.c:426
> #174 0x000000000063abc6 in Flet (args=34224035) at eval.c:946
> #175 0x000000000063da93 in eval_sub (form=34224019) at eval.c:2119
> #176 0x0000000000638e97 in Fprogn (body=34223987) at eval.c:426
> #177 0x000000000063da93 in eval_sub (form=34224003) at eval.c:2119
> #178 0x0000000000638c13 in Fif (args=34223955) at eval.c:383
> #179 0x000000000063da93 in eval_sub (form=34223971) at eval.c:2119
> #180 0x0000000000638e97 in Fprogn (body=34223875) at eval.c:426
> #181 0x000000000064047c in funcall_lambda (fun=34223731, nargs=2, arg_vector=0x7fffffffce38) at eval.c:2914
> #182 0x000000000063fac8 in Ffuncall (nargs=3, args=0x7fffffffce30) at eval.c:2754
> #183 0x000000000063e9d9 in Fapply (nargs=2, args=0x7fffffffcf00) at eval.c:2321
> #184 0x000000000063f040 in apply1 (fn=18936912, arg=60814083) at eval.c:2537
> #185 0x000000000069c5f0 in read_process_output_call (fun_and_args=60814067) at process.c:5237
> #186 0x000000000063bb67 in internal_condition_case_1 (bfun=0x69c566 <read_process_output_call>, arg=60814067, handlers=18960, hfun=0x69f534 <exec_sentinel_error_handler>)
>     at eval.c:1333
> #187 0x000000000069f700 in exec_sentinel (proc=45524853, reason=51837972) at process.c:6590
> #188 0x000000000069f94b in status_notify (deleting_process=0x0, wait_proc=0x0) at process.c:6692
> #189 0x000000000069ac7b in wait_reading_process_output (time_limit=30, nsecs=0, read_kbd=-1, do_display=true, wait_for_cell=0, wait_proc=0x0, just_wait_proc=0) at process.c:4674
> #190 0x00000000004273d2 in sit_for (timeout=122, reading=true, display_option=1) at dispnew.c:5751
> #191 0x00000000005916a7 in read_char (commandflag=1, map=60824323, prev_event=0, used_mouse_menu=0x7fffffffd759, end_time=0x0) at keyboard.c:2700
> #192 0x00000000005a1963 in read_key_sequence (keybuf=0x7fffffffd930, bufsize=30, prompt=0, dont_downcase_last=false, can_return_switch_frame=true, fix_current_buffer=true, 
>     prevent_redisplay=false) at keyboard.c:9024
> #193 0x000000000058d96c in command_loop_1 () at keyboard.c:1344
> #194 0x000000000063bacd in internal_condition_case (bfun=0x58d51d <command_loop_1>, handlers=18960, hfun=0x58cb65 <cmd_error>) at eval.c:1309
> #195 0x000000000058d14b in command_loop_2 (ignore=0) at keyboard.c:1087
> #196 0x000000000063b09e in internal_catch (tag=45744, func=0x58d122 <command_loop_2>, arg=0) at eval.c:1074
> #197 0x000000000058d0eb in command_loop () at keyboard.c:1066
> #198 0x000000000058c64a in recursive_edit_1 () at keyboard.c:672
> #199 0x000000000058c84f in Frecursive_edit () at keyboard.c:743
> #200 0x000000000058a559 in main (argc=1, argv=0x7fffffffdd58) at emacs.c:1656
> (gdb) 

Can anyone guess what's going on based on the stacktrace? Are there other commands I should run in GDB next time the problem occurs?

Thanks!
Clément.