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+# InsTrim
+
+InsTrim: Lightweight Instrumentation for Coverage-guided Fuzzing
+
+## Introduction
+
+InsTrim is the work of Chin-Chia Hsu, Che-Yu Wu, Hsu-Chun Hsiao and Shih-Kun Huang.
+
+It uses a CFG (call flow graph) and markers to instrument just what
+is necessary in the binary (ie less than llvm_mode). As a result the binary is
+about 10-15% faster compared to normal llvm_mode however with some coverage loss.
+It requires at least llvm version 3.8.0 to build.
+If you have LLVM 7+ we recommend PCGUARD instead.
+
+## Usage
+
+Set the environment variable `AFL_LLVM_INSTRUMENT=CFG` or `AFL_LLVM_INSTRIM=1`
+during compilation of the target.
+
+There is also special mode which instruments loops in a way so that
+afl-fuzz can see which loop path has been selected but not being able to
+see how often the loop has been rerun.
+This again is a tradeoff for speed for less path information.
+To enable this mode set `AFL_LLVM_INSTRIM_LOOPHEAD=1`.
+
+## Background
+
+The paper from Chin-Chia Hsu, Che-Yu Wu, Hsu-Chun Hsiao and Shih-Kun Huang:
+[InsTrim: Lightweight Instrumentation for Coverage-guided Fuzzing]
+(https://www.ndss-symposium.org/wp-content/uploads/2018/07/bar2018_14_Hsu_paper.pdf)