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Symbiosis Tutorial

Consider using Cortex, a tool that extends Symbiosis to expose concurrency bugs (that may depend on both the path and the schedule), in addition to finding their root cause.

Symbiosis is a tool to help developers diagnose concurrency bugs by computing differential schedule projections. For more information check our PLDI'15 paper.

Symbiosis for C/C++

Download VM with everything already set up here:


$ cd SymbiosisRuntime
$ make
  • Build Symbiosis Symbolic Execution Engine:
$ cd SymbiosisSE
$ make
  • Build Symbiosis Symbolic Solver:
$ cd SymbiosisSolver
$ make

Example: Crasher

  • Compile and run instrumented version:
$ cd Tests/CTests/crasher 
$ make Run
$ export SYMBTRACE=$PWD/crasher.trace
$ export LD_LIBRARY_PATH=/path/to/SymbiosisRuntime
$ ./CrasherRUN_inst

This will create an execution path trace with extension .ok (in case of a successful execution) or .fail (in case of a failing execution).

  • Run symbolic execution with the generated path trace:
$ make KLEE
$ /path/to/SymbiosisSE/Release+Asserts/bin/symbiosisse --allow-external-sym-calls --bb-trace=$PWD/ CrasherKLEE_inst.bc

This will generate the symbolic trace files into folder klee-last.

  • Run symbiosis solver to find the failing schedule:
$ cd /path/to/SymbiosisSolver
$ ./symbiosisSolver --trace-folder=/path/to/Tests/CTests/crasher/klee-last --model=$PWD/tmp/modelCrasher.txt --solution=$PWD/tmp/failCrasher.txt --with-solver=/path/to/z3-folder/bin/z3

If the solver yields satisfiable, it will store the failing scheduel into failCrasher.txt.

  • Run symbiosis solver to find an alternate non-failing schedule and generate a differential schedule projection (DSP):
$ ./symbiosisSolver --model=$PWD/tmp/modelCrasher.txt --solution=$PWD/tmp/failCrasher.txt --with-solver=/path/to/z3-folder/bin/z3 --source=/path/to/Tests/CTests/crasher/ --fix-mode

If the solver finds a valid alternate schedule, it will output a graphviz file containing the DSP (extension .gv) into folder SymbiosisSolver/tmp/DSP.

  • (Optional) Create a .ps version of the DSP:
$ cd ./tmp/DSP
$ dot -Tps dsp_failCrasher_Alt0.gv -o


Symbiosis - Concurrency Debugging via Differential Schedule Projections



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