bug#42931: 27.1; json-pretty-print-buffer on ~2MB line causes core dump

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Wed, 19 Aug 2020 16:15:38 +0200
> Cc: 42931@debbugs.gnu.org
> 
> Phil Sainty <psainty@orcon.net.nz> writes:
> 
> > On my system, Emacs hangs for quite a while and then core dumps.
> 
> I can confirm that this leads to a segmentation fault (on Debian).
> 
> [Current thread is 1 (Thread 0x7fbbb1c04000 (LWP 2154403))]
> (gdb) bt
> #0  raise (sig=<optimized out>) at ../sysdeps/unix/sysv/linux/raise.c:50
> #1  0x000055d08b0a0ac9 in terminate_due_to_signal
>     (sig=sig@entry=11, backtrace_limit=backtrace_limit@entry=40) at 
> emacs.c:408
> #2  0x000055d08b0a0f5f in handle_fatal_signal (sig=sig@entry=11)
>     at sysdep.c:1786
> #3  0x000055d08b19bf9d in deliver_thread_signal
>     (sig=sig@entry=11, handler=0x55d08b0a0f54 <handle_fatal_signal>)
>     at sysdep.c:1760
> #4  0x000055d08b19c019 in deliver_fatal_thread_signal (sig=11) at 
> sysdep.c:1883
> #5  handle_sigsegv (sig=11, siginfo=<optimized out>, arg=<optimized out>)
>     at sysdep.c:1883
> #6  0x00007fbbb530d140 in <signal handler called> ()
>     at /lib/x86_64-linux-gnu/libpthread.so.0
> #7  0x000055d08b1f7a43 in compareseq
>     (xoff=xoff@entry=897, xlim=xlim@entry=17383858, yoff=yoff@entry=1353, 
> ylim=ylim@entry=25500750, find_minimal=false, ctxt=ctxt@entry=0x7fff5bfa5610)
>     at ../lib/diffseq.h:472
> #8  0x000055d08b1f7d94 in compareseq (xoff=<optimized out>, 
>     xoff@entry=897, xlim=xlim@entry=17383882, yoff=yoff@entry=1353, 
> ylim=ylim@entry=25500806, find_minimal=false, ctxt=ctxt@entry=0x7fff5bfa5610)
>     at ../lib/diffseq.h:510

looks like stack overflow?  I guess the recursive nature of compareseq
is got to cause this at some point?