tor/doc/HACKING/HelpfulTools.md

Useful tools

These aren't strictly necessary for hacking on Tor, but they can help track down bugs.

Jenkins

https://jenkins.torproject.org

Dmalloc

The dmalloc library will keep track of memory allocation, so you can find out if we're leaking memory, doing any double-frees, or so on.

dmalloc -l -/dmalloc.log
(run the commands it tells you)
./configure --with-dmalloc

Valgrind

valgrind --leak-check=yes --error-limit=no --show-reachable=yes src/or/tor

(Note that if you get a zillion openssl warnings, you will also need to pass --undef-value-errors=no to valgrind, or rebuild your openssl with -DPURIFY.)

Coverity

Nick regularly runs the coverity static analyzer on the Tor codebase.

The preprocessor define __COVERITY__ is used to work around instances where coverity picks up behavior that we wish to permit.

clang Static Analyzer

The clang static analyzer can be run on the Tor codebase using Xcode (WIP) or a command-line build.

The preprocessor define __clang_analyzer__ is used to work around instances where clang picks up behavior that we wish to permit.

clang Runtime Sanitizers

To build the Tor codebase with the clang Address and Undefined Behavior sanitizers, see the file contrib/clang/sanitize_blacklist.txt.

Preprocessor workarounds for instances where clang picks up behavior that we wish to permit are also documented in the blacklist file.

Running lcov for unit test coverage

Lcov is a utility that generates pretty HTML reports of test code coverage. To generate such a report:

./configure --enable-coverage
make
make coverage-html
$BROWSER ./coverage_html/index.html

This will run the tor unit test suite ./src/test/test and generate the HTML coverage code report under the directory ./coverage_html/. To change the output directory, use make coverage-html HTML_COVER_DIR=./funky_new_cov_dir.

Coverage diffs using lcov are not currently implemented, but are being investigated (as of July 2014).

Running the unit tests

To quickly run all the tests distributed with Tor:

make check

To run the fast unit tests only:

make test

To selectively run just some tests (the following can be combined arbitrarily):

./src/test/test <name_of_test> [<name of test 2>] ...
./src/test/test <prefix_of_name_of_test>.. [<prefix_of_name_of_test2>..] ...
./src/test/test :<name_of_excluded_test> [:<name_of_excluded_test2]...

To run all tests, including those based on Stem or Chutney:

make test-full

To run all tests, including those based on Stem or Chutney that require a working connection to the internet:

make test-full-online

Running gcov for unit test coverage

./configure --enable-coverage
make
make check
# or--- make test-full ? make test-full-online?
mkdir coverage-output
./scripts/test/coverage coverage-output

(On OSX, you'll need to start with --enable-coverage CC=clang.)

Then, look at the .gcov files in coverage-output. '-' before a line means that the compiler generated no code for that line. '######' means that the line was never reached. Lines with numbers were called that number of times.

If that doesn't work:

• Try configuring Tor with --disable-gcc-hardening
• You might need to run make clean after you run ./configure.

If you make changes to Tor and want to get another set of coverage results, you can run make reset-gcov to clear the intermediary gcov output.

If you have two different coverage-output directories, and you want to see a meaningful diff between them, you can run:

./scripts/test/cov-diff coverage-output1 coverage-output2 | less

In this diff, any lines that were visited at least once will have coverage "1". This lets you inspect what you (probably) really want to know: which untested lines were changed? Are there any new untested lines?

Running integration tests

We have the beginnings of a set of scripts to run integration tests using Chutney. To try them, set CHUTNEY_PATH to your chutney source directory, and run make test-network.

We also have scripts to run integration tests using Stem. To try them, set STEM_SOURCE_DIR to your Stem source directory, and run test-stem.

Profiling Tor with oprofile

The oprofile tool runs (on Linux only!) to tell you what functions Tor is spending its CPU time in, so we can identify performance bottlenecks.

Here are some basic instructions

• Build tor with debugging symbols (you probably already have, unless you messed with CFLAGS during the build process).
• Build all the libraries you care about with debugging symbols (probably you only care about libssl, maybe zlib and Libevent).
• Copy this tor to a new directory
• Copy all the libraries it uses to that dir too (ldd ./tor will tell you)
• Set LD_LIBRARY_PATH to include that dir. ldd ./tor should now show you it's using the libs in that dir
• Run that tor
• Reset oprofiles counters/start it
  • opcontrol --reset; opcontrol --start, if Nick remembers right.
• After a while, have it dump the stats on tor and all the libs in that dir you created.
  • opcontrol --dump;
  • opreport -l that_dir/*
• Profit

Generating and analyzing a callgraph

1. Run ./scripts/maint/generate_callgraph.sh. This will generate a bunch of files in a new ./callgraph directory.

2. Run ./scripts/maint/analyze_callgraph.py callgraph/src/*/*. This will do a lot of graph operations and then dump out a new callgraph.pkl file, containing data in Python's 'pickle' format.

3. Run ./scripts/maint/display_callgraph.py. It will display:

   • the number of functions reachable from each function.
   • all strongly-connnected components in the Tor callgraph
   • the largest bottlenecks in the largest SCC in the Tor callgraph.

Note that currently the callgraph generator can't detect calls that pass through function pointers.

Getting emacs to edit Tor source properly

Nick likes to put the following snippet in his .emacs file:

(add-hook 'c-mode-hook
      (lambda ()
        (font-lock-mode 1)
        (set-variable 'show-trailing-whitespace t)

        (let ((fname (expand-file-name (buffer-file-name))))
          (cond
           ((string-match "^/home/nickm/src/libevent" fname)
            (set-variable 'indent-tabs-mode t)
            (set-variable 'c-basic-offset 4)
            (set-variable 'tab-width 4))
           ((string-match "^/home/nickm/src/tor" fname)
            (set-variable 'indent-tabs-mode nil)
            (set-variable 'c-basic-offset 2))
           ((string-match "^/home/nickm/src/openssl" fname)
            (set-variable 'indent-tabs-mode t)
            (set-variable 'c-basic-offset 8)
            (set-variable 'tab-width 8))
        ))))

You'll note that it defaults to showing all trailing whitespace. The cond test detects whether the file is one of a few C free software projects that I often edit, and sets up the indentation level and tab preferences to match what they want.

If you want to try this out, you'll need to change the filename regex patterns to match where you keep your Tor files.

If you use emacs for editing Tor and nothing else, you could always just say:

(add-hook 'c-mode-hook
    (lambda ()
        (font-lock-mode 1)
        (set-variable 'show-trailing-whitespace t)
        (set-variable 'indent-tabs-mode nil)
        (set-variable 'c-basic-offset 2)))

There is probably a better way to do this. No, we are probably not going to clutter the files with emacs stuff.

Doxygen

We use the 'doxygen' utility to generate documentation from our source code. Here's how to use it:

1. Begin every file that should be documented with

    /**
     * \file filename.c
     * \brief Short description of the file.
     */
   

   (Doxygen will recognize any comment beginning with /** as special.)

2. Before any function, structure, #define, or variable you want to document, add a comment of the form:

   /** Describe the function's actions in imperative sentences.
    *
    * Use blank lines for paragraph breaks
    *   - and
    *   - hyphens
    *   - for
    *   - lists.
    *
    * Write <b>argument_names</b> in boldface.
    *
    * \code
    *     place_example_code();
    *     between_code_and_endcode_commands();
    * \endcode
    */
   

3. Make sure to escape the characters <, >, \, % and # as \<, \>, \\, \% and \#.

4. To document structure members, you can use two forms:

   struct foo {
     /** You can put the comment before an element; */
     int a;
     int b; /**< Or use the less-than symbol to put the comment
            * after the element. */
   };
   

5. To generate documentation from the Tor source code, type:

   $ doxygen -g
   

   to generate a file called Doxyfile. Edit that file and run doxygen to generate the API documentation.

6. See the Doxygen manual for more information; this summary just scratches the surface.