1 files changed, 19 insertions, 2 deletions
diff --git a/docs/custom_mutators.md b/docs/custom_mutators.md
index 4ffeda7a..a1de479e 100644
--- a/docs/custom_mutators.md
+++ b/docs/custom_mutators.md
@@ -48,6 +48,7 @@ C/C++:
 ```c
 void *afl_custom_init(afl_state_t *afl, unsigned int seed);
 unsigned int afl_custom_fuzz_count(void *data, const unsigned char *buf, size_t buf_size);
+void afl_custom_splice_optout(void *data);
 size_t afl_custom_fuzz(void *data, unsigned char *buf, size_t buf_size, unsigned char **out_buf, unsigned char *add_buf, size_t add_buf_size, size_t max_size);
 const char *afl_custom_describe(void *data, size_t max_description_len);
 size_t afl_custom_post_process(void *data, unsigned char *buf, size_t buf_size, unsigned char **out_buf);
@@ -72,6 +73,9 @@ def init(seed):
 def fuzz_count(buf):
     return cnt
 
+def splice_optout()
+    pass
+
 def fuzz(buf, add_buf, max_size):
     return mutated_out
 
@@ -114,7 +118,7 @@ def deinit():  # optional for Python
 
 ### Custom Mutation
 
-- `init`:
+- `init` (optional in Python):
 
     This method is called when AFL++ starts up and is used to seed RNG and set
     up buffers and state.
@@ -132,6 +136,13 @@ def deinit():  # optional for Python
     for a specific queue entry, use this function. This function is most useful
     if `AFL_CUSTOM_MUTATOR_ONLY` is **not** used.
 
+- `splice_optout` (optional):
+
+    If this function is present, no splicing target is passed to the `fuzz`
+    function. This saves time if splicing data is not needed by the custom
+    fuzzing function.
+    This function is never called, just needs to be present to activate.
+
 - `fuzz` (optional):
 
     This method performs custom mutations on a given input. It also accepts an
@@ -139,6 +150,7 @@ def deinit():  # optional for Python
     sense to use it. You would only skip this if `post_process` is used to fix
     checksums etc. so if you are using it, e.g., as a post processing library.
     Note that a length > 0 *must* be returned!
+    The returned output buffer is under **your** memory management!
 
 - `describe` (optional):
 
@@ -172,6 +184,11 @@ def deinit():  # optional for Python
     to the target, e.g. if it is too short, too corrupted, etc. If so,
     return a NULL buffer and zero length (or a 0 length string in Python).
 
+    NOTE: Do not make any random changes to the data in this function!
+
+    PERFORMANCE for C/C++: If possible make the changes in-place (so modify
+    the `*data` directly, and return it as `*outbuf = data`.
+
 - `fuzz_send` (optional):
 
     This method can be used if you want to send data to the target yourself,
@@ -190,7 +207,7 @@ def deinit():  # optional for Python
     discovered if compiled with INTROSPECTION. The custom mutator can then
     return a string (const char *) that reports the exact mutations used.
 
-- `deinit`:
+- `deinit` (optional in Python):
 
     The last method to be called, deinitializing the state.