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#About#

SeaHorn is an automated analysis framework for LLVM-based languages.

#License# SeaHorn is distributed under a modified BSD license. See license.txt for details.

#Installation#

• cd seahorn ; mkdir build ; cd build
• cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=run ../
• (optional) cmake --build . --target extra to download extra packages
• cmake --build . to build dependencies (Z3 and LLVM)
• (optional) cmake --build . to build extra packages (crab-llvm)
• cmake --build . to build seahorn
• cmake --build . --target install to install everything in run directory

SeaHorn and dependencies are installed in build/run

Optional components can be installed individually as well:

• dsa-seahorn: git clone https://github.com/seahorn/dsa-seahorn.git

• crab-llvm: git clone https://github.com/seahorn/crab-llvm.git

• llvm-seahorn: git clone https://github.com/seahorn/llvm-seahorn.git

Note that both dsa-seahorn and crab-llvm are optional. Nevertheless both are highly recommended. The former is needed when reasoning about memory contents while the latter provides inductive invariants using abstract interpretation techniques to the rest of SeaHorn's backends.

Latest news: due to some unsolved licensing issues crab-llvm is temporary not publicly available. Please, if this impacts your current project do not hesitate to contact us at seahorn@aguga.net.

#Usage#

SeaHorn provides a python script called sea to interact with users. Given a C program annotated with assertions, users just need to type: sea pf file.c

This will output unsat if all assertions hold or otherwise sat if any of the assertions is violated. The option pf tells SeaHorn to translate file.c into LLVM bitecode, generate a set of verification conditions (VCs), and finally, solve them. This command uses as main default options:

• --step=large: large-step encoding. Each step corresponds to a loop-free program block.

• --step=small: small-step encoding. Each step corresponds to a basic block.

• --track=mem: model both scalars, pointers, and memory contents

• --track=ptr : model registers and pointers (but not memory content)

• --track=reg : model registers only

• --inline : inlines the program before verification

• --cex=FILE : stores a counter-example in FILE

• --crab : generates invariants using the Crab abstract-interpretation-based tool. Read here for details about Crab options. This option is currently disabled.

• -g : compiles with debug information for more trackable counterexamples.

sea pf is a pipeline that runs multiple commands. Individual parts of the pipeline can be ran separately as well:

1. sea fe file.c -o file.bc: SeaHorn frontend translates a C program into optimized LLVM bitcode including mixed-semantics transformation.

2. sea horn file.bc -o file.smt2: SeaHorn generates the verification conditions from file.bc and outputs them into SMT-LIB v2 format. Users can choose between different encoding styles with several levels of precision by adding:

   • --step={small,large,fsmall,flarge} where small is small step encoding, large is block-large encoding, fsmall is small step encoding producing flat Horn clauses (i.e., it generates a transition system with only one predicate), and flarge: block-large encoding producing flat Horn clauses.

   • --track={reg,ptr,mem} where reg only models integer scalars, ptr models reg and pointer addresses, and mem models ptr and memory contents.

3. sea smt file.c -o file.smt2: Generates CHC in SMT-LIB2 format. Is an alias for sea fe followed by sea horn. The command sea pf is an alias for sea smt --prove.

4. sea clp file.c -o file.clp: Generates CHC in CLP format.

5. sea lfe file.c -o file.ll : runs the legacy front-end

To see all the options, type sea --help.

##Annotating C programs##

This is an example of a C program annotated with a safety property:

    /* verification command: sea pf --horn-stats test.c */
    #include "seahorn/seahorn.h"
    int nd();

    int main(void){
      int k=1;
      int i=1;
      int j=0;
      int n = nd();
      while(i<n) {
        j=0;
        while(j<i) {
          k += (i-j);
          j++;
        }
        i++;
      }
      sassert(k>=n);
    }

SeaHorn follows SV-COMP convention of encoding error locations by a call to the designated error function __VERIFIER_error(). SeaHorn returns unsat when __VERIFIER_error() is unreachable, and the program is considered safe. SeaHorn returns sat when __VERIFIER_error() is reachable and the program is unsafe. sassert() method is defined in seahorn/seahorn.h which can be found in seahorn/share.

#People#

• Arie Gurfinkel
• Jorge Navas
• Temesghen Kahsai