bug#34394: 27.0.50; Emacs segfaults with SLY, company and C-g

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 10 Feb 2019 18:42:40 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 34394@debbugs.gnu.org
> 
> >   src/emacs -Q -L path/to/company-mode -l company -l foo.el -f foo-test-bug
> 
> Thanks, this reproduces the problem with 100% probability, and I'm
> looking into the problem.

I think I found the culprit.  Please see if the patch below fixes the
problem, including the one you had in the real-life scenario and
environment.

diff --git a/src/keyboard.c b/src/keyboard.c
index 49c687f..f6550f7 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -365,6 +365,7 @@ static Lisp_Object make_lispy_focus_out (Lisp_Object);
 static bool help_char_p (Lisp_Object);
 static void save_getcjmp (sys_jmp_buf);
 static void restore_getcjmp (sys_jmp_buf);
+static void unwind_getcjmp (void *);
 static Lisp_Object apply_modifiers (int, Lisp_Object);
 static void restore_kboard_configuration (int);
 static void handle_interrupt (bool);
@@ -2144,12 +2145,14 @@ read_event_from_main_queue (struct timespec *end_time,
     return c;
 
   /* Actually read a character, waiting if necessary.  */
+  ptrdiff_t count = SPECPDL_INDEX ();
   save_getcjmp (save_jump);
+  record_unwind_protect_ptr (unwind_getcjmp, &save_jump);
   restore_getcjmp (local_getcjmp);
   if (!end_time)
     timer_start_idle ();
   c = kbd_buffer_get_event (&kb, used_mouse_menu, end_time);
-  restore_getcjmp (save_jump);
+  unbind_to (count, Qnil);
 
   if (! NILP (c) && (kb != current_kboard))
     {
@@ -2638,10 +2641,12 @@ read_char (int commandflag, Lisp_Object map,
 	{
 	  Lisp_Object tem0;
 
+	  ptrdiff_t count = SPECPDL_INDEX ();
 	  save_getcjmp (save_jump);
+	  record_unwind_protect_ptr (unwind_getcjmp, &save_jump);
 	  restore_getcjmp (local_getcjmp);
 	  tem0 = sit_for (Vecho_keystrokes, 1, 1);
-	  restore_getcjmp (save_jump);
+	  unbind_to (count, Qnil);
 	  if (EQ (tem0, Qt)
 	      && ! CONSP (Vunread_command_events))
 	    echo_now ();
@@ -2712,10 +2717,12 @@ read_char (int commandflag, Lisp_Object map,
 
 	  timeout = min (timeout, MOST_POSITIVE_FIXNUM / delay_level * 4);
 	  timeout = delay_level * timeout / 4;
+	  ptrdiff_t count1 = SPECPDL_INDEX ();
 	  save_getcjmp (save_jump);
+	  record_unwind_protect_ptr (unwind_getcjmp, &save_jump);
 	  restore_getcjmp (local_getcjmp);
 	  tem0 = sit_for (make_number (timeout), 1, 1);
-	  restore_getcjmp (save_jump);
+	  unbind_to (count1, Qnil);
 
 	  if (EQ (tem0, Qt)
 	      && ! CONSP (Vunread_command_events))
@@ -3329,6 +3336,14 @@ restore_getcjmp (sys_jmp_buf temp)
 {
   memcpy (getcjmp, temp, sizeof getcjmp);
 }
+
+static void
+unwind_getcjmp (void *ptr)
+{
+  sys_jmp_buf jbuf;
+  memcpy (jbuf, *(sys_jmp_buf *)ptr, sizeof getcjmp);
+  restore_getcjmp (jbuf);
+}
 \f
 /* Low level keyboard/mouse input.
    kbd_buffer_store_event places events in kbd_buffer, and