bug#20471: Emacs ceased to respond to C-g on a tty; SIGINT became blocked?

[Ivan Shmakov <ivan@siamics.net>]

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>>>>> Andreas Schwab <schwab@linux-m68k.org> writes:
>>>>> Ivan Shmakov <ivan@siamics.net> writes:

 >> Attaching GDB to it shows no signals being delivered on C-g, which
 >> (AIUI) hints at either SIGINT being blocked /or/ C-g “unbound” from
 >> the signal via terminal settings.  I’ve copied the latter from a
 >> terminal used by a properly working Emacs instance with the stty(1)
 >> invocation below, yet I still see no signals via GDB, which leaves
 >> the signal mask as the only point of failure that I can think of.

 >> Any suggestion on how do I debug this issue any further?

 > A blocked signal would still be visible in the debugger

	It’s not what I observe.  Why, SIGINT seem to be ignored by GDB
	itself when it’s attached to that Emacs instance.

 > (assuming you haven't changed the handling of SIGINT in gdb).

	I didn’t.

(gdb) info signals 
Signal        Stop      Print   Pass to program Description

SIGHUP        Yes       Yes     Yes             Hangup
SIGINT        Yes       Yes     No              Interrupt
SIGQUIT       Yes       Yes     Yes             Quit
…

	Just in case, the ps(1) output for two of my Emacs instances
	goes below.  The GDB ‘bt’ output at SIGCONT time (after a
	properly handled C-z) is MIMEd, too.

	To note is that I’ve tried to set a breakpoint on the next line
	of internal_catch (), but it doesn’t seem to ever be triggered.
	Could it hint at some non-local exit issue, perhaps?

$ ps -o pid,pending,blocked,ignored,caught,stat,bsdtime,command \
      -C emacs24 -C emacs25 
  PID   PENDING   BLOCKED   IGNORED    CAUGHT STAT   TIME COMMAND
19987  00000000  00000000  14001000 <cb816eff S+   843:01 emacs24
25806  00000002  04002006  04001000 <db816eff Sl+   52:00 emacs25
$ 

-- 
FSF associate member #7257  http://am-1.org/~ivan/      … 3013 B6A0 230E 334A

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(gdb) bt 
#0  0x00007f4cb4d13f0a in tcsetattr () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00000000004a5e71 in emacs_set_tty (fd=5, 
    settings=settings@entry=0x7fffb46cfaf0, flushp=flushp@entry=false)
    at sysdep.c:850
#2  0x00000000004a6c84 in init_sys_modes (tty_out=0x12c20c0) at sysdep.c:1079
#3  0x00000000004a6f18 in init_all_sys_modes () at sysdep.c:907
#4  0x00000000004fcce2 in unbind_to (count=<optimized out>, value=0)
    at eval.c:3217
#5  0x000000000049d8f5 in Fsuspend_emacs (stuffstring=0) at keyboard.c:10266
#6  0x00000000004fdf13 in Ffuncall (nargs=5, args=0x7b0250 <Ssuspend_emacs>)
    at eval.c:2718
#7  0x0000000000530073 in exec_byte_code (bytestr=<optimized out>, 
    vector=9208813, maxdepth=<optimized out>, args_template=<optimized out>, 
    nargs=<optimized out>, args=<optimized out>) at bytecode.c:919
#8  0x00000000004fdd33 in Ffuncall (nargs=5, nargs@entry=1, 
    args=0x8c8390 <pure+1118096>) at eval.c:2779
#9  0x00000000004f9b3a in Ffuncall_interactively (nargs=1, args=0x7fffb46cff88)
    at callint.c:252
#10 0x00000000004fde19 in Ffuncall (nargs=5, nargs@entry=2, 
    args=0xa95dd8 <Sfuncall_interactively>) at eval.c:2698
#11 0x00000000004ff18c in Fapply (nargs=nargs@entry=3, 
    args=args@entry=0x7fffb46cff80) at eval.c:2289
#12 0x00000000004f9e98 in Fcall_interactively (function=3671376, 
    record_flag=0, keys=<optimized out>) at callint.c:394
#13 0x00000000004fdef7 in Ffuncall (nargs=5, 
    args=0xa95da8 <Scall_interactively>) at eval.c:2725
#14 0x0000000000530073 in exec_byte_code (bytestr=<optimized out>, 
    vector=8964949, maxdepth=<optimized out>, args_template=<optimized out>, 
    nargs=<optimized out>, args=<optimized out>) at bytecode.c:919
#15 0x00000000004fdd33 in Ffuncall (nargs=5, nargs@entry=2, 
    args=0x88cb00 <pure+874240>) at eval.c:2779
#16 0x00000000004fdfea in call1 (fn=fn@entry=12096, arg1=<optimized out>)
    at eval.c:2573
#17 0x000000000049c90d in command_loop_1 () at keyboard.c:1521
#18 0x00000000004fc617 in internal_condition_case (
    bfun=bfun@entry=0x49c520 <command_loop_1>, handlers=handlers@entry=15888, 
    hfun=hfun@entry=0x493a50 <cmd_error>) at eval.c:1348
#19 0x000000000048f5ac in command_loop_2 (ignore=ignore@entry=0)
    at keyboard.c:1139
#20 0x00000000004fc4f3 in internal_catch (tag=tag@entry=40992, 
    func=func@entry=0x48f590 <command_loop_2>, arg=arg@entry=0) at eval.c:1108
#21 0x000000000048f569 in command_loop () at keyboard.c:1118
#22 0x0000000000493666 in recursive_edit_1 () at keyboard.c:728
#23 0x0000000000493980 in Frecursive_edit () at keyboard.c:799
#24 0x0000000000407f78 in main (argc=1, argv=0x7fffb46d05e8) at emacs.c:1626
(gdb)