update debugging information in readme file

diff --git a/doc/README.txt b/doc/README.txt
index 268b9afabd664fb6dda2be85fb8863941c850c72..ddb8763c9ec22c975bd0ad15a1d695455cbd2c50 100644 (file)
--- a/doc/README.txt
+++ b/doc/README.txt
@@ -27,3 +27,18 @@ Run the model checker.
 
 Use dot (from graphviz) to convert the outputted dot files into the
 format of your choice.
+
+III. Using the debugger (gdb).
+
+You can launch the debugger by passing in the gdb option to run.sh (or
+you can lok at run.sh to see how to launch the model checker from
+within a debugger).  Since we trap SIGSEGV to detect pages that we
+need to update, you have to disable stopping on SIGSEGV.  To do this,
+use the following commands:
+
+To run inside MacOS under gdb you need (lldb won't work as far as I know):
+set dont-handle-bad-access 1 (sometime not necessary)
+handle SIGBUS nostop noprint
+
+To run in Linux under gdb, use:
+handle SIGSEGV nostop noprint