tmp: add segfault reproduce insns

hypervisor.md

@@ -127,3 +127,42 @@ $ ${CROSS_COMPILE}strip lkvm-static
 ```
 
 The above commands will create `kvmtool/lkvm-static` that you need to copy to your host root file system.
+
+## kvmtool segfault reproduce
+
+The segfault bug does not reproduce each time the hypervisor lauches. The reproducibility depends on the delays in the code, e.g. executing `sleep` or putting more printfs influences the reproducibility. The usual reproducibility rate is around 13-16%. It is also important to mention that virtio driver should be used (`-n virtio`) to reproduce the issue.
+
+The issue reproduces by booting hypervisor with no command:
+```
+/hp/lkvm-static run --kernel /hp/Image --console serial --params "console=ttyS0 earlycon=sbi" -n virtio -d /hp/rootfs-virt.ext2 -m 100M
+```
+
+To test issue fixes I crafted a script that executes the hypervisor 100 times and checks the output fot segfault.
+
+```
+#!/bin/sh
+
+SEG_FAULT_COUNT=0
+TOTAL_RUNS=100
+CURRENT_RUN=1
+FILE=.test_file
+
+while [ "$CURRENT_RUN" -le "$TOTAL_RUNS" ]; do
+  /hp/lkvm-static run --kernel /hp/Image --console serial --params "console=ttyS0 earlycon=sbi -- /benchmarks/sleep; dmesg" -d /hp/rootfs-virt.ext2 -n virtio -m 100M &> $FILE
+  segfault=$(cat $FILE | grep "Segmentation fault")
+
+  if [ -z "$segfault" ]; then
+    echo "Run $CURRENT_RUN: No segmentation fault"
+  else
+    SEG_FAULT_COUNT=$((SEG_FAULT_COUNT + 1))
+    cat $FILE
+    echo "Run $CURRENT_RUN: Segmentation fault"
+  fi
+
+  CURRENT_RUN=$((CURRENT_RUN + 1))
+done
+
+rm $FILE
+
+echo "Total Segmentation Faults: $SEG_FAULT_COUNT out of $TOTAL_RUNS runs"
+```