CBMC is a model checker for C. This means that CBMC will explore all possible paths through your code on all possible inputs, and will check that all assertions in your code are true. CBMC can also check for the possibility of memory safety errors (like buffer overflow) and for instances of undefined behavior (like signed integer overflow). CBMC is a bounded model checker, however, which means that using CBMC may require restricting this set of all possible inputs to inputs of some bounded size.

CBMC Viewer is a tool that scans the output of CBMC and produces a browsable summary of its findings.

Here is a simple example of using cbmc-viewer. Running this example requires installing CBMC. Installation on MacOS is just brew install cbmc. Installation on other operation systems is described on the CBMC release page.

Create a source file main.c containing

#include <stdlib.h>

static int global;

int main() {
  int *ptr = malloc(sizeof(int));

  assert(global > 0);
  assert(*ptr > 0);

  return 0;
}

and run the commands

goto-cc -o main.goto main.c
cbmc main.goto --trace --xml-ui > result.xml
cbmc main.goto --cover location --xml-ui > coverage.xml
cbmc main.goto --show-properties --xml-ui > property.xml
cbmc-viewer --goto main.goto --result result.xml --coverage coverage.xml --property property.xml --srcdir .

and open the report created by cbmc-viewer in a web browser with

open report/html/index.html

What you will see is

• A coverage report summarizing what lines of source code were exercised by cbmc. In this case, coverage is 100%. Clicking on main, you can see the source code for main annotated with coverage data (all lines are green because all lines were hit).

• A bug report summarizing what issues cbmc found with the code. In this case, the bugs are violations of the assertions because, for example, it is possible that the uninitialized integer allocated on the heap contains a negative value. For each bug, there is a link to

  • The line of code where the bug occurred.

  • An error trace showing the steps of the program leading to the bug. For each step, there a link to the line of code that generated the step, making it easy to follow the error trace and root cause the bug.

Most people should just follow the instructions on the release page.

Developers can install the package in Python "development mode" as follows. First, follow the instructions on the release page to install the dependencies. Then,

• Clone the repository with

  git clone https://github.com/model-checking/cbmc-viewer cbmc-viewer
  
• Install development mode with

  cd cbmc-viewer
  make develop
  export PATH=$PATH:$(pwd)
  
• Uninstall development mode with

  cd cbmc-viewer
  make undevelop
  

This training material is a work in progress. If you have suggestions, corrections, or questions, contact us by submitting a GitHub issue. If you have some training of your own that you would like to contribute, submit your contributions as a GitHub pull request.