Installation instructions

This document provides basic installation instructions and discusses known issues for a variety of platforms.


Linux on x86

This platform is expected to work well. Compile the program with:

$ make

You can start using the fuzzer without installation, but it is also possible to install it with:

# make install

There are no special dependencies to speak of; you will need GNU make and a working compiler (gcc or clang). Some of the optional scripts bundled with the program may depend on bash, gdb, and similar basic tools.

If you are using clang, please review llvm_mode/README.llvm; the LLVM integration mode can offer substantial performance gains compared to the traditional approach.

You may have to change several settings to get optimal results (most notably, disable crash reporting utilities and switch to a different CPU governor), but afl-fuzz will guide you through that if necessary.

OpenBSD, FreeBSD, NetBSD on x86

Similarly to Linux, these platforms are expected to work well and are regularly tested. Compile everything with GNU make:

$ gmake

Note that BSD make will not work; if you do not have gmake on your system, please install it first. As on Linux, you can use the fuzzer itself without installation, or install it with:

# gmake install

Keep in mind that if you are using csh as your shell, the syntax of some of the shell commands given in the README and other docs will be different.

The llvm_mode requires a dynamically linked, fully-operational installation of clang. At least on FreeBSD, the clang binaries are static and do not include some of the essential tools, so if you want to make it work, you may need to follow the instructions in llvm_mode/README.llvm.

Beyond that, everything should work as advertised.

The QEMU mode is currently supported only on Linux. I think it’s just a QEMU problem, I couldn’t get a vanilla copy of user-mode emulation support working correctly on BSD at all.

MacOS X on x86

MacOS X should work, but there are some gotchas due to the idiosyncrasies of the platform. On top of this, I have limited release testing capabilities and depend mostly on user feedback.

To build AFL, install Xcode and follow the general instructions for Linux.

The Xcode ‘gcc’ tool is just a wrapper for clang, so be sure to use afl-clang to compile any instrumented binaries; afl-gcc will fail unless you have GCC installed from another source (in which case, please specify AFL_CC and AFL_CXX to point to the “real” GCC binaries).

Only 64-bit compilation will work on the platform; porting the 32-bit instrumentation would require a fair amount of work due to the way OS X handles relocations, and today, virtually all MacOS X boxes are 64-bit.

The crash reporting daemon that comes by default with MacOS X will cause problems with fuzzing. You need to turn it off by following the instructions provided here:

The fork() semantics on OS X are a bit unusual compared to other unix systems and definitely don’t look POSIX-compliant. This means two things:

  • Fuzzing will be probably slower than on Linux. In fact, some folks report considerable performance gains by running the jobs inside a Linux VM on MacOS X.
  • Some non-portable, platform-specific code may be incompatible with the AFL forkserver. If you run into any problems, set AFL_NO_FORKSRV=1 in the environment before starting afl-fuzz.

User emulation mode of QEMU does not appear to be supported on MacOS X, so black-box instrumentation mode (-Q) will not work.

The llvm_mode requires a fully-operational installation of clang. The one that comes with Xcode is missing some of the essential headers and helper tools. See llvm_mode/README.llvm for advice on how to build the compiler from scratch.

Linux or *BSD on non-x86 systems

Standard build will fail on non-x86 systems, but you should be able to leverage two other options:

  • The LLVM mode (see llvm_mode/README.llvm), which does not rely on x86-specific assembly shims. It’s fast and robust, but requires a complete installation of clang.
  • The QEMU mode (see qemu_mode/README.qemu), which can be also used for fuzzing cross-platform binaries. It’s slower and more fragile, but can be used even when you don’t have the source for the tested app.

If you’re not sure what you need, you need the LLVM mode. To get it, try:

$ AFL_NO_X86=1 gmake && gmake -C llvm_mode

…and compile your target program with afl-clang-fast or afl-clang-fast++ instead of the traditional afl-gcc or afl-clang wrappers.

Solaris on x86

The fuzzer reportedly works on Solaris, but I have not tested this first-hand, and the user base is fairly small, so I don’t have a lot of feedback.

To get the ball rolling, you will need to use GNU make and GCC or clang. I’m being told that the stock version of GCC that comes with the platform does not work properly due to its reliance on a hardcoded location for ‘as’ (completely ignoring the -B parameter or $PATH).

To fix this, you may want to build stock GCC from the source, like so:

$ ./configure --prefix=$HOME/gcc --with-gnu-as --with-gnu-ld \
  --with-gmp-include=/usr/include/gmp --with-mpfr-include=/usr/include/mpfr
$ make
$ sudo make install

Do not specify --with-as=/usr/gnu/bin/as - this will produce a GCC binary that ignores the -B flag and you will be back to square one.

Note that Solaris reportedly comes with crash reporting enabled, which causes problems with crashes being misinterpreted as hangs, similarly to the gotchas for Linux and MacOS X. AFL does not auto-detect crash reporting on this particular platform, but you may need to run the following command:

$ coreadm -d global -d global-setid -d process -d proc-setid \
  -d kzone -d log

User emulation mode of QEMU is not available on Solaris, so black-box instrumentation mode (-Q) will not work.

Everything else

You’re on your own. On POSIX-compliant systems, you may be able to compile and run the fuzzer; and the LLVM mode may offer a way to instrument non-x86 code.

The fuzzer will not run on Windows. It will also not work under Cygwin. It could be ported to the latter platform fairly easily, but it’s a pretty bad idea, because Cygwin is extremely slow. It makes much more sense to use VirtualBox or so to run a hardware-accelerated Linux VM; it will run around 20x faster or so. If you have a really compelling use case for Cygwin, let me know.

Although Android on x86 should theoretically work, the stock kernel may have SHM support compiled out, and if so, you may have to address that issue first. It’s possible that all you need is this workaround:

Joshua J. Drake notes that the Android linker adds a shim that automatically intercepts SIGSEGV and related signals. To fix this issue and be able to see crashes, you need to put this at the beginning of the fuzzed program:

signal(SIGILL, SIG_DFL);
signal(SIGBUS, SIG_DFL);
signal(SIGFPE, SIG_DFL);

You may need to #include <signal.h> first.