> From: Reuben Thomas <rrt@sc3d.org>
> Date: Sat, 8 Oct 2016 00:12:26 +0100
>
> In both cases, the crash occurs while Emacs is lazy-loading my desktop.

What does "lazy-loading" mean in this context?

> I can't tell exactly what it's doing, but it appears to be about the
> same place each time.

If you run Emacs under GDB, and source the src/.gdbinit file provided
in the source tree, the backtrace command will automatically try to
produce a Lisp-level backtrace as well.  That could be helpful.

This string in the 1st backtrace you show could help figure out what
form was being evaluated:

  #41 0x000000000059af2d in read_process_output (coding=0x53b3920, nbytes=652, chars=0x7fff0376eaa0
  "Unescaped left brace in regex is deprecated, passed through in regex; marked by <-- HERE in m/\\\\begin{
  <-- HERE tex}(.*?)\\\\end{tex}/ at /usr/bin/texify line 521.\nUnescaped left brace in regex is depre"..., p=0x287)
  at process.c:5440

The SIGSEGV happens here:

      nextsym:
        if (ptr->gcmarkbit)  <<<<<<<<<<<<<<<<<<
          break;

So the value of 'ptr' there (frame 20 in the 1st backtrace) is of
interest.