added the grammar mutator as a git submodule + documentation

.gitmodules

@@ -1,3 +1,7 @@
 [submodule "unicorn_mode/unicornafl"]
 	path = unicorn_mode/unicornafl
-	url = https://github.com/AFLplusplus/unicornafl.git
+	url = https://github.com/AFLplusplus/unicornafl
+
+[submodule "custom_mutators/Grammar-Mutator"]
+	path = custom_mutators/Grammar-Mutator
+	url = https://github.com/AFLplusplus/Grammar-Mutator

custom_mutators/README.md

@@ -3,6 +3,22 @@
 Custom mutators enhance and alter the mutation strategies of afl++.
 For further information and documentation on how to write your own, read [the docs](../docs/custom_mutators.md).
 
+## The afl++ Grammar Mutator
+
+If you use git to clone afl++, then the following will incorporate our
+excellent grammar custom mutator:
+```
+git submodule init
+git submodule update
+```
+
+otherwise just checkout the repository here with either
+`git clone https://github.com/AFLplusplus/Grammar-Mutator` or
+`svn co https://github.com/AFLplusplus/Grammar-Mutator`.
+
+Read the [Grammar-Mutator/README.md](Grammar-Mutator/README.md) on how to use
+it.
+
 ## Production-Ready Custom Mutators
 
 This directory holds ready to use custom mutators.

docs/Changelog.md

@@ -10,20 +10,24 @@ sending a mail to <afl-users+subscribe@googlegroups.com>.
 
 
 ### Version ++2.67d (develop)
+  - added the GSoC excellent afl++ grammar mutator by Shengtuo to our
+    custom_mutators/ (see custom_mutators/README.md) - or get it here:
+    https://github.com/AFLplusplus/Grammar-Mutator
   - a few QOL changes for Apple and its outdated gmake
   - afl-fuzz:
     - Fix for auto dictionary entries found during fuzzing to not throw out
       a -x dictionary
     - added total execs done to plot file
-    - AFL_MAX_DET_EXTRAS env variable added to control the amount of deterministic
-      dict entries without recompiling.
-    - AFL_FORKSRV_INIT_TMOUT env variable added to control the time to wait for
-      the forkserver to come up without the need to increase the overall timeout.
+    - AFL_MAX_DET_EXTRAS env variable added to control the amount of
+      deterministic dict entries without recompiling.
+    - AFL_FORKSRV_INIT_TMOUT env variable added to control the time to wait
+      for the forkserver to come up without the need to increase the overall
+      timeout.
     - bugfix for cmplog that results in a heap overflow based on target data
       (thanks to the magma team for reporting!)
   - custom mutators:
-    - added afl_custom_fuzz_count/fuzz_count function to allow specifying the 
-      number of fuzz attempts for custom_fuzz
+    - added afl_custom_fuzz_count/fuzz_count function to allow specifying
+      the number of fuzz attempts for custom_fuzz
   - llvm_mode:
     - Ported SanCov to LTO, and made it the default for LTO. better
       instrumentation locations