Handle C stack overflow caused by too nested Lisp evaluation.

* configure.ac: Check for sigaltstack and related sigaction
support.  Unconditionally check for sigsetjmp and siglongjmp.
(HAVE_STACK_OVERFLOW_HANDLING): Define if we can support it.
* src/lisp.h (toplevel) [HAVE_STACK_OVERFLOW_HANDLING]: Declare
siglongjmp point to transfer control from SIGSEGV handler.
* src/keyboard.c (return_to_command_loop, recover_top_level_message)
[HAVE_STACK_OVERFLOW_HANDLING]: New variables.
(regular_top_level_message): New variable.
(command_loop) [HAVE_STACK_OVERFLOW_HANDLING]: Handle non-local
exit from SIGSEGV handler and adjust message displayed by Vtop_level
if appropriate.
(syms_of_keyboard): DEFVAR Vtop_level_message and initialize
new variables described above.
* src/sysdep.c [HAVE_SYS_RESOURCE_H]: Include sys/resource.h as such.
(stack_grows_down, sigsegv_stack, handle_sigsegv)
[HAVE_STACK_OVERFLOW_HANDLING]: New variables and function.
(init_sigsegv): New function.
(init_signals): Use it.
* lisp/startup.el (normal-top-level): Use top-level-message.

1 files changed, 33 insertions, 0 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index 9b0b19ada2f..ed00b38a7db 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -133,6 +133,19 @@ static ptrdiff_t this_single_command_key_start;
 static ptrdiff_t before_command_key_count;
 static ptrdiff_t before_command_echo_length;
 
+#ifdef HAVE_STACK_OVERFLOW_HANDLING
+
+/* For longjmp to recover from C stack overflow.  */
+sigjmp_buf return_to_command_loop;
+
+/* Message displayed by Vtop_level when recovering from C stack overflow.  */
+static Lisp_Object recover_top_level_message;
+
+#endif /* HAVE_STACK_OVERFLOW_HANDLING */
+
+/* Message normally displayed by Vtop_level.  */
+static Lisp_Object regular_top_level_message;
+
 /* For longjmp to where kbd input is being done.  */
 
 static sys_jmp_buf getcjmp;
@@ -1134,6 +1147,17 @@ static Lisp_Object top_level_1 (Lisp_Object);
 Lisp_Object
 command_loop (void)
 {
+#ifdef HAVE_STACK_OVERFLOW_HANDLING  
+  /* At least on GNU/Linux, saving signal mask is important here.  */
+  if (sigsetjmp (return_to_command_loop, 1) != 0)
+    {
+      /* Comes here from handle_sigsegv, see sysdep.c.  */
+      init_eval ();
+      Vtop_level_message = recover_top_level_message;
+    }
+  else
+    Vtop_level_message = regular_top_level_message;
+#endif /* HAVE_STACK_OVERFLOW_HANDLING */
   if (command_loop_level > 0 || minibuf_level > 0)
     {
       Lisp_Object val;
@@ -11000,6 +11024,15 @@ syms_of_keyboard (void)
   Vlispy_mouse_stem = build_pure_c_string ("mouse");
   staticpro (&Vlispy_mouse_stem);
 
+  regular_top_level_message = build_pure_c_string ("Back to top level");
+#ifdef HAVE_STACK_OVERFLOW_HANDLING
+  recover_top_level_message
+    = build_pure_c_string ("Re-entering top level after C stack overflow");
+#endif  
+  DEFVAR_LISP ("top-level-message", Vtop_level_message,
+               doc: /* Message displayed by `normal-top-level'.  */);
+  Vtop_level_message = regular_top_level_message;
+
   /* Tool-bars.  */
   DEFSYM (QCimage, ":image");
   DEFSYM (Qhelp_echo, "help-echo");