Merge pull request #1759 from AFLplusplus/dev

Dev

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+# Target Intelligence
+
+These are some ideas you can do so that your target that you are fuzzing can
+give helpful feedback to AFL++.
+
+## Add to the AFL++ dictionary from your target
+
+For this you target must be compiled for CMPLOG (`AFL_LLVM_CMPLOG=1`).
+
+Add in your source code:
+
+```
+__attribute__((weak)) void __cmplog_rtn_hook_strn(u8 *ptr1, u8 *ptr2, u64 len);
+__attribute__((weak)) void __cmplog_ins_hook1(uint8_t arg1, uint8_t arg2, uint8_t attr);
+__attribute__((weak)) void __cmplog_ins_hook2(uint16_t arg1, uint16_t arg2, uint8_t attr);
+__attribute__((weak)) void __cmplog_ins_hook4(uint32_t arg1, uint32_t arg2, uint8_t attr);
+__attribute__((weak)) void __cmplog_ins_hook8(uint64_t arg1, uint64_t arg2, uint8_t attr);
+
+int in_your_function(...) {
+
+  // to add two strings to the AFL++ dictionary:
+  if (__cmplog_rtn_hook_strn)
+    __cmplog_rtn_hook_strn(string1, length_of_string1, string2, length_of_string2);
+
+  // to add two 32 bit integers to the AFL++ dictionary:
+  if (__cmplog_ins_hook4)
+    __cmplog_ins_hook4(first_32_bit_var, second_32_bit_var, 0);
+
+}
+```
+
+Note that this only makes sense if these values are in-depth processed in the
+target in a way that AFL++ CMPLOG cannot uncover these, e.g. if these values
+are transformed by a matrix computation.
+
+Fixed values are always better to give to afl-fuzz via a `-x dictionary`.
+
+## Add inputs to AFL++ dictionary from your target
+
+If for whatever reason you want your target to propose new inputs to AFL++,
+then this is actually very easy.
+The environment variable `AFL_CUSTOM_INFO_OUT` contains the output directory
+of this run - including the fuzzer instance name (e.g. `default`), so if you
+run `afl-fuzz -o out -S foobar`, the value would be `out/foobar`).
+
+To show afl-fuzz an input it should consider just do the following:
+
+1. create the directory `$AFL_CUSTOM_INFO_OUT/../target/queue`
+2. create any new inputs you want afl-fuzz to notice in that directory with the
+   following naming convention: `id:NUMBER-OF-LENGTH-SIX-WITH-LEADING-ZEROES,whatever`
+   where that number has to be increasing.
+   e.g.:
+```
+   id:000000,first_file
+   id:000001,second_file
+   id:000002,third_file
+   etc.
+```
+
+Note that this will not work in nyx_mode because afl-fuzz cannot see inside the
+virtual machine.