New frame type to block bad unwinding and cont capture.

If some external function is invoked which can call back
into TXR Lisp, we should guard against the called-back
code from capturing a continuation across the external
stack frames, and also from unwinding across those
frames. This patch prepares a mechanism for this.

* unwind.c (uw_unwind_to_exit_point): Abort with message on
standard error if attempt is made to unwind across UW_GUARD
frame.
(uw_push_guard): New function.
(uw_capture_cont): If the frame search
encounters a UW_GUARD block, an exception is thrown.

* unwind.h (enum uw_frtype): New enum constant, UW_GUARD.
(uw_push_guard): Declared.

0 files changed, 0 insertions, 0 deletions