% clang -emit-llvm -c -g -O0 -Xclang -disable-O0-optnone -I /tmp/klee_src/include/klee/ klee_CRC64.c

% time klee --libc=uclibc --optimize klee_CRC64.bc

...

KLEE: done: total instructions = 17036
KLEE: done: completed paths = 1
KLEE: done: partially completed paths = 32
KLEE: done: generated tests = 3

real    2m47.538s
user    2m46.299s
sys     0m0.619s

% ls klee-last/*
klee-last/assembly.ll   klee-last/solver-queries.smt2  klee-last/test000002.ktest
klee-last/info          klee-last/test000001.kquery    klee-last/test000002.user.err
klee-last/messages.txt  klee-last/test000001.ktest     klee-last/test000003.ktest
klee-last/run.istats    klee-last/test000001.user.err  klee-last/warnings.txt
klee-last/run.stats     klee-last/test000002.kquery

% ktest-tool klee-last/test000001.ktest | grep data
object 0: data: b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

% ktest-tool klee-last/test000002.ktest | grep data
object 0: data: b'Hello, world!.. aaaaaaaaaaaaaa\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff'

% ktest-tool klee-last/test000003.ktest | grep data
object 0: data: b'Hello, world!.. xnzhtcktymchxy ... and goodbye'