no -M/-S: auto-set -S default

3 files changed, 23 insertions, 14 deletions

diff --git a/README.md b/README.md
index 819da093..384ae830 100644
--- a/README.md
+++ b/README.md
@@ -28,28 +28,30 @@
 ## Major changes in afl++ 3.0
 
 With afl++ 3.0 we introduced changes that break some previous afl and afl++
-behaviours:
+behaviours and defaults:
 
   * There are no llvm_mode and gcc_plugin subdirectories anymore and there is
     only one compiler: afl-cc. All previous compilers now symlink to this one
     compiler. All instrumentation source code is now in the `instrumentation/`
     folder.
-  * The gcc_plugin was replaced with a new version submitted by AdaCore, that
-    supports more features, thank you!
+  * The gcc_plugin was replaced with a new version submitted by AdaCore that
+    supports more features. thank you!
   * qemu_mode got upgraded to QEMU 5.1, but to be able to build this a current
     ninja build tool version and python3 setuptools are required.
     qemu_mode also got new options like snapshotting, instrumenting specific
-    shared libraries, etc. and QEMU 5.1 supports more CPU targets so this is
-    worth it.
+    shared libraries, etc. Additionally QEMU 5.1 supports more CPU targets so
+    this is really worth it.
   * When instrumenting targets, afl-cc will not supersede optimizations. This
     allows to fuzz targets as same as they are built for debug or release.
-  * afl-fuzz':
-    * `-i` option now descends into subdirectories.
+  * afl-fuzz:
+    * if neither -M or -S is specified, `-S default` is assumed, so more
+      fuzzers can easily be added later
+    * `-i` input directory option now descends into subdirectories. It also
+      does not fatal on crashes and too large files, instead it skips them
+      and uses them for splicing mutations
     * -m none is now default, set memory limits (in MB) with e.g. -m 250
     * deterministic fuzzing is now disabled by default (unless using -M) and
       can be enabled with -D
-  * afl-fuzz will skip over empty dictionaries and too-large test cases instead
-    of failing, and use them as a source for splicing mutations
 
 ## Contents
 
diff --git a/docs/Changelog.md b/docs/Changelog.md
index f15f1d93..36022399 100644
--- a/docs/Changelog.md
+++ b/docs/Changelog.md
@@ -23,6 +23,7 @@ sending a mail to <afl-users+subscribe@googlegroups.com>.
       with -M)
     - statsd support by Edznux, thanks a lot!
     - Marcel Boehme submitted a patch that improves all AFFast schedules :)
+    - not specifying -M or -S will now auto-set "-S default"
     - reading testcases from -i now descends into subdirectories
     - allow up to 4 -x command line options
     - loaded extras now have a duplicate protection
diff --git a/src/afl-fuzz.c b/src/afl-fuzz.c
index 004adffe..d42a0d36 100644
--- a/src/afl-fuzz.c
+++ b/src/afl-fuzz.c
@@ -411,8 +411,8 @@ int main(int argc, char **argv_orig, char **envp) {
 
         if (afl->sync_id) { FATAL("Multiple -S or -M options not supported"); }
         afl->sync_id = ck_strdup(optarg);
-        afl->skip_deterministic = 0; // force determinsitic fuzzing
-        afl->old_seed_selection = 1; // force old queue walking seed selection
+        afl->skip_deterministic = 0;  // force determinsitic fuzzing
+        afl->old_seed_selection = 1;  // force old queue walking seed selection
 
         if ((c = strchr(afl->sync_id, ':'))) {
 
@@ -847,6 +847,8 @@ int main(int argc, char **argv_orig, char **envp) {
       "Eißfeldt, Andrea Fioraldi and Dominik Maier");
   OKF("afl++ is open source, get it at "
       "https://github.com/AFLplusplus/AFLplusplus");
+  OKF("NOTE: This is v3.x which changes several defaults and behaviours - see "
+      "README.md");
 
   if (afl->sync_id && afl->is_main_node &&
       afl->afl_env.afl_custom_mutator_only) {
@@ -1135,15 +1137,19 @@ int main(int argc, char **argv_orig, char **envp) {
     WARNF("it is wasteful to run more than one main node!");
     sleep(1);
 
-  }
-
-  if (afl->is_secondary_node && check_main_node_exists(afl) == 0) {
+  } else if (afl->is_secondary_node && check_main_node_exists(afl) == 0) {
 
     WARNF(
         "no -M main node found. It is recommended to run exactly one main "
         "instance.");
     sleep(1);
 
+  } else if (!afl->sync_id) {
+
+    afl->sync_id = "default";
+    afl->is_secondary_node = 1;
+    OKF("no -M/-S set, autoconfiguring for \"-S %s\"", afl->sync_id);
+
   }
 
   #ifdef RAND_TEST_VALUES