On platforms with sigaltstack, TXR programs can now catch the

segmentation fault that occurs when running out of stack space,
and escape by throwing an exception.

Also, bugfix: save and restore the gc enable/disable state.  Without
this, if we are ever running cod in a gc disabled state and it jumps
out, gc stays disabled.

* configure: added check for sigaltstack.

* gc.h (gc_enabled): Declaration added for existing variable.

* signal.c (is_cpu_exception): New static function.
(sig_handler): For cpu_exception type signals that pertain
to the execution of some instruction, turn on async_sig_enabled,
so that the signal is not deferred. Otherwise we will just
return without calling the user-defined handler, restart
the instruction and get into a loop. Also, disable gc around
the handler just in case. One issue is that we might be on
an alternate stack, which gc won't like.
(setup_alt_stack, teardown_alt_stack): New static functions.
(set_sig_handler): If we have sigaltstack, and are asked
to set up a SEGV handler, then set it up on the alternate
stack.

* signal.h (extended_jmp_buf): Adding new member, gc.
(extended_setjmp, extended_longjmp): use gc member
to save and restore the gc_enable state across
setjmp and longjmp.

1 files changed, 2 insertions, 0 deletions

diff --git a/gc.h b/gc.h
index ba7c5777..345cdadb 100644
--- a/gc.h
+++ b/gc.h
@@ -43,6 +43,8 @@ val gc_mutated(val);
 void unmark(void);
 void gc_hint_func(val *);
 
+extern int gc_enabled;
+
 #if EXTRA_DEBUGGING
 val break_obj;
 #endif