Merge branch 'master' into readme_example

README.md

@@ -245,13 +245,22 @@ ERROR: Failed: Runlength_EncodeDecode
 By default, DeepState is not very verbose about testing activity,
 other than failing tests.  The `--log_level` argument lowers the
 threshold for output, with 0 = `DEBUG`, 1 = `TRACE` (output from the
-tests, including `printf`), 2 = `INFO` (DeepState messages; this is the default), 3 = `WARNING`,
+tests, including from `printf`), 2 = INFO (DeepState messages, the default), 3 = `WARNING`,
 4 = `ERROR`, 5 = `EXTERNAL` (output from other programs such as
-libFuzzer), and 6 = `CRITICAL`/`FATAL` messages.  Lowering the `log_level` can be very
+libFuzzer), and 6 = `CRITICAL` messages.  Lowering the `log_level` can be very
 useful for understanding what a DeepState harness is actually doing;
 often, setting `--log_level 1` in either fuzzing or symbolic
 execution will give sufficient information to debug your test harness.
 
+## A Note on Mac OS and Forking
+
+Normally, when running a test for replay or fuzzing, DeepState forks
+in order to cleanly handle crashes of a test.  Unfortunately, `fork()`
+on mac OS is extremely slow.  When using the built-in fuzzer or
+replaying tests, it is highly recommended to add the `--no_fork`
+option on mac OS, unless you need the added crash handling (that is,
+things aren't working without that option).
+
 ## Built-In Fuzzer
 
 Every DeepState executable provides a simple built-in fuzzer that