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+# afl-untracer - fast fuzzing of binary-only libraries
+
+## Introduction
+
+afl-untracer is an example skeleton file which can easily be used to fuzz
+a closed source library.
+
+It requires less memory and is x3-5 faster than qemu_mode however it is way
+more course grained and does not provide interesting features like compcov
+or cmplog.
+
+Supported is so far Intel (i386/x86_64) and AARCH64.
+
+## How-to
+
+### Modify afl-untracer.c
+
+Read and modify afl-untracer.c then `make`.
+To adapt afl-untracer.c to your needs, read the header of the file and then
+search and edit the `STEP 1`, `STEP 2` and `STEP 3` locations.
+
+### Generate patches.txt file
+
+To generate the `patches.txt` file for your target library use the
+`ida_get_patchpoints.py` script for IDA Pro or
+`ghidra_get_patchpoints.java` for Ghidra.
+
+The patches.txt file has to be pointed to by `AFL_UNTRACER_FILE`.
+
+To easily run the scripts without needing to run the GUI with Ghidra:
+```
+/opt/ghidra/support/analyzeHeadless /tmp/ tmp$$ -import libtestinstr.so -postscript ./ghidra_get_patchpoints.java
+rm -rf /tmp/tmp$$
+```
+The file is created at `~/Desktop/patches.txt`
+
+### Fuzzing
+
+Example (after modifying afl-untracer.c to your needs, compiling and creating
+patches.txt):
+```
+LD_LIBRARY_PATH=/path/to/target/library AFL_UNTRACER_FILE=./patches.txt afl-fuzz -i in -o out -- ./afl-untracer
+```
+(or even remote via afl-network-proxy).
+
+### Testing and debugging
+
+For testing/debugging you can try:
+```
+make DEBUG=1
+AFL_UNTRACER_FILE=./patches.txt AFL_DEBUG=1 gdb ./afl-untracer
+```
+and then you can easily set breakpoints to "breakpoint" and "fuzz".
+
+# Background
+
+This idea is based on [UnTracer](https://github.com/FoRTE-Research/UnTracer-AFL)
+and modified by [Trapfuzz](https://github.com/googleprojectzero/p0tools/tree/master/TrapFuzz).
+This implementation is slower because the traps are not patched out with each
+run, but on the other hand gives much better coverage information.