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Overview of the auxiliary tools provided by KLEE



KLEE can be configured to output .ktest files whenever it finds an error, covers new code or terminates a path. The content of a .ktest file describes the program input that is needed to guide a concrete execution exactly along the corresponding execution path. Typically, it comprises concrete values for symbolic input files, symbolic arguments, and symbolic variables introduced with klee_make_symbolic. The ktest-tool is a Python script that converts the contents of a .ktest file into human-readable form. For instance for the get_sign.c example from the KLEE directory it would print a concrete value for the symbolic 32bit integer a in different representations (Python byte string, hexadecimal, little-endian uint/int, …):

$ ktest-tool klee-last/test000003.ktest
ktest file : 'klee-last/test000003.ktest'
args       : ['get_sign.bc']
num objects: 1
object 0: name: 'a'
object 0: size: 4
object 0: data: b'\\x00\\x00\\x00\\x80'
object 0: hex : 0x00000080
object 0: int : -2147483648
object 0: uint: 2147483648
object 0: text: ....


klee-stats is a Python script used to extract and present statistics from run.stats files present in KLEE’s klee-out-* directories. klee-stats can be invoked on a single directory or list of directories:

$ klee-stats klee-out-2
|   Path   |  Instrs|  Time(s)|  ICov(%)|  BCov(%)|  ICount|  TSolver(%)|
|klee-out-2|     499|     0.09|    45.69|    39.13|     394|        0.03|
$ klee-stats .
|   Path   |  Instrs|  Time(s)|  ICov(%)|  BCov(%)|  ICount|  TSolver(%)|
|klee-last |     499|     0.13|    45.69|    39.13|     394|        0.04|
|klee-out-3|     499|     0.03|    45.69|    39.13|     394|        0.12|
|klee-out-2|     499|     0.09|    45.69|    39.13|     394|        0.03|
|klee-out-8|     499|     0.13|    45.69|    39.13|     394|        0.04|
|klee-out-4|     499|     0.02|    45.69|    39.13|     394|        0.14|
|Total (5) |    2495|     0.40|    45.69|    39.13|    1970|        0.07|

This is only a small subset of statistics that KLEE keeps track of during execution. By using --print-all, a much larger set can be displayed:

Statistic Description
Instrs number of executed instructions
Time(s) total wall time
ICov(%) instruction coverage in the LLVM bitcode
BCov(%) conditional branch (br) coverage in the LLVM bitcode
ICount total static instructions in the LLVM bitcode
TSolver(%) relative time spent in the solver chain wrt wall time (incl. caches and constraint solver)
ICovered total covered instructions in the LLVM bitcode
IUncovered total uncovered instructions in the LLVM bitcode
Branches number of conditional branch (br) instructions in the LLVM bitcode
FullBranches number of fully-explored conditional branch (br) instructions in the LLVM bitcode
PartialBranches number of partially-explored conditional branch (br) instructions in the LLVM bitcode
ExternalCalls number of external calls
TUser(s) total user time
TResolve(s) time spent in object resolution
TResolve(%) relative time spent in object resolution wrt wall time
TCex(s) time spent in the counterexample caching code (incl. constraint solver)
TCex(%) relative time spent in the counterexample caching code wrt wall time (incl. constraint solver)
TQuery(s) time spent in the constraint solver
TSolver(s) time spent in the solver chain (incl. caches and constraint solver)
States number of created states
ActiveStates number of currently active states (0 after successful termination)
MaxActiveStates maximum number of active states
AvgActiveStates average number of active states
InhibitedForks number of inhibited state forks due to e.g. memory pressure
Queries number of queries issued to the solver chain
SolverQueries number of queries issued to the constraint solver
SolverQueryConstructs number of query constructs for all queries send to the constraint solver
AvgSolverQuerySize average number of query constructs per query issued to the constraint solver
QCacheMisses Query cache misses
QCacheHits Query cache hits
QCexCacheMisses Counterexample cache misses
QCexCacheHits Counterexample cache hits
Allocations number of allocated heap objects of the program under test
Mem(MiB) mebibytes of memory currently used
MaxMem(MiB) maximum memory usage
AvgMem(MiB) average memory usage
BrConditional number of forks caused by symbolic branch conditions (br)
BrIndirect number of forks caused by indirect branches (indirectbr) with symbolic address
BrSwitch number of forks caused by switch with symbolic value
BrCall number of forks caused by symbolic function pointers
BrMemOp number of forks caused by memory operation with symbolic address
BrResolvePointer number of forks caused by symbolic pointers
BrAlloc number of forks caused by symbolic allocation size
BrRealloc number of forks caused by symbolic reallocation size
BrFree number of forks caused by freeing a symbolic pointer
BrGetVal number of forks caused by user-invoked concretization while seeding
TermExit number of states that reached end of execution path
TermEarly number of early terminated states (e.g. due to memory pressure, state limt)
TermSolverErr number of states terminated due to solver errors
TermProgrErr number of states terminated due to program errors (e.g. division by zero)
TermUserErr number of states terminated due to user errors (e.g. misuse of KLEE API)
TermExecErr number of states terminated due to execution errors (e.g. unsupported intrinsics)
TermEarlyAlgo number of state terminations required by algorithm (e.g. state merging or replaying)
TermEarlyUser number of states terminated via klee_silent_exit()
TArrayHash(s) time spent hashing arrays (if KLEE_ARRAY_DEBUG enabled, otherwise -1)
TFork(s) time spent forking states
TFork(%) relative time spent forking states wrt wall time
TUser(%) relative user time wrt wall time

In order to limit printed information only to the values of measured times, the following options can be used:

Several table styles are supported (e.g. csv, latex_booktabs or html) that can be enabled with --table-format=<format>, e.g.:

$ klee-stats --table-format=readable-csv klee-out-2 klee-out-3
Path      ,  Instrs,  Time(s),  ICov(%),  BCov(%),  ICount,  TSolver(%)
klee-out-2,     499,     0.09,    45.69,    39.13,     394,        0.03
klee-out-3,     499,     0.03,    45.69,    39.13,     394,        0.12

Various other options can be used to specify what values are displayed and how they are displayed. Options for comparison of statistics are also provided. More information about available options can be obtained using the command:

$ klee-stats --help

Conversion to comma-separated values (csv)

Starting with version 2.0, KLEE switched from csv to SQLite3 to store its statistics. Of course, these files can be opened and queried with any SQLite client, e.g.:

$ sqlite3 <klee-out-dir>/run.stats
> SELECT * FROM stats

The easiest way to convert the entries for all statistics from a single run.stats file to comma-separated values (csv) is to use klee-stats with the --to-csv flag. If the output needs to be modified or limited to specific columns and rows an SQLite client such as sqlite3 comes handy:

$ sqlite3 -csv -header run.stats "select Instructions,printf(\"%.2f\",100.0*CoveredInstructions/(CoveredInstructions+UncoveredInstructions)) AS 'Icov(%)',printf(\"%.2f\",1.0*SolverTime/60000000) AS 'SolverTime(min)',NumQueries from stats ORDER BY WallTime DESC LIMIT 1" 

Live-monitoring with Grafana

klee-stats can also be used as a Grafana data-source. This enables you to create Grafana dashboards for live monitoring of your KLEE process. First, klee-stats needs to be started with the -grafana flag to start serving the data:

$ klee-stats --grafana <klee-out-dir>

Which starts on port 5000 by default. Then you can start the preconfigured Grafana Docker image with:

$ docker run -d --net=host --name=grafana klee/grafana

This will create a daemon container running Grafana on port 3000. The image may take half a minute or so to start up. Go to http://localhost:3000, then click on ‘Home’ in the top left hand corner and select the dashboard named ‘KLEE’ from the dropdown.

If you would like to see the progress as Grafana starts, you can instead run Grafana in the foreground by omitting the -d flag. Grafana is ready when the output stops and you see a line like this:

t=... lvl=info msg="HTTP Server Listen" logger=http.server address= protocol=http subUrl= socket=

If you are using Grafana to view the statistics of a KLEE run that has already finished, make sure to select a time range that includes the time when KLEE was running. The time range can be changed by with the dropdown in the top right corner.

You can then of course customize your dashboard, add more panels change time ranges and enjoy the live monitoring of KLEE.

To stop Grafana:

$ docker stop grafana

Or if Grafana is running in the foreground then use Ctrl-C.

Logging granularity

The intervals at which KLEE writes its statistics are configurable. All times are lower bounds and a long running solver query might prevent KLEE from writing new entries.


A tool for generating a .ktest file from a concrete input. The contents and format of the generated .ktest is the same as that described above (similarly, it can be converted into a human-readable form using ktest-tool). The .ktest file can be replayed in KLEE (e.g., to generate the path conditions for a concrete input) and used as an interesting seed.

For example, suppose that you had previous fuzzed a target application with the American Fuzzy Lop (AFL) fuzzer. After fuzzing, the input queue/ contains the set of testcases that produced new state transitions. The testcases in the queue can be converted to .ktest files so that they can be further-explored in KLEE:

# Assumes that you are in the AFL output directory (specified via the `-o` option when fuzzing.
# Ignores hidden directories.
# AFL-generated testcases always begin with 'id:'

find ./queue -not -path '*/\.*' -type f -name 'id:*'    \
    -exec ktest-gen --bout-file {}.ktest --sym-file {} \;

KLEE can subsequently be run with the -seed-dir option to seed further exploration.


Similar to ktest-gen, except that it generates random data for the .ktest file.


When KLEE was used with --write-exec-tree, klee-exec-tree can be used to show various statistics of the execution tree, e.g. branch information and information about the termination types of paths:

Example usage:

$ klee-exec-tree branches klee-out-1
branch type,count

$ klee-exec-tree terminations klee-out-1
termination type,count

It also can be used to dump the tree in Graphviz.dot format to generate .png/.svg files. We recommend .svg as it shows tooltips with e.g. state id, asm line, branch type.

$ klee-exec-tree tree-dot klee-out-1 | dot -Tsvg > tree.svg