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# laf-intel instrumentation
## Introduction
This originally is the work of an individual nicknamed laf-intel. His blog
[Circumventing Fuzzing Roadblocks with Compiler Transformations](https://lafintel.wordpress.com/)
and GitLab repo [laf-llvm-pass](https://gitlab.com/laf-intel/laf-llvm-pass/)
describe some code transformations that help AFL++ to enter conditional blocks,
where conditions consist of comparisons of large values.
## Usage
By default, these passes will not run when you compile programs using
afl-clang-fast. Hence, you can use AFL++ as usual. To enable the passes, you
must set environment variables before you compile the target project.
The following options exist:
`export AFL_LLVM_LAF_SPLIT_SWITCHES=1`
Enables the split-switches pass.
`export AFL_LLVM_LAF_TRANSFORM_COMPARES=1`
Enables the transform-compares pass (strcmp, memcmp, strncmp, strcasecmp,
strncasecmp).
`export AFL_LLVM_LAF_SPLIT_COMPARES=1`
Enables the split-compares pass. By default, it will
1. simplify operators >= (and <=) into chains of > (<) and == comparisons
2. change signed integer comparisons to a chain of sign-only comparison and
unsigned integer comparisons
3. split all unsigned integer comparisons with bit widths of 64, 32, or 16 bits
to chains of 8 bits comparisons.
You can change the behavior of the last step by setting `export
AFL_LLVM_LAF_SPLIT_COMPARES_BITW=<bit_width>`, where bit_width may be 64, 32, or
16. For example, a bit_width of 16 would split larger comparisons down to 16 bit
comparisons.
A new unique feature is splitting floating point comparisons into a series
of sign, exponent and mantissa comparisons followed by splitting each of them
into 8 bit comparisons when necessary. It is activated with the
`AFL_LLVM_LAF_SPLIT_FLOATS` setting.
Note that setting this automatically activates `AFL_LLVM_LAF_SPLIT_COMPARES`.
You can also set `AFL_LLVM_LAF_ALL` and have all of the above enabled. :-)
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