CoFlo 0.0.4 User's Manual

Copyright © 2011, 2012 Gary R. Van Sickle

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

Table of Contents

About CoFlo

CoFlo is a Free and Open Source source code analysis tool which generates and analyzes control flow graphs from C and C++ source.  CoFlo is distributed under the terms of the GNU General Public License Version 3.

The CoFlo home page is graciously hosted by SourceForge at the following URL:


CoFlo's ultimate target audience is all developers in need of a deeper inspection, analysis, and understanding of their C and C++ source code.  As of this alpha release however, CoFlo's target audience is early adopters who fit the prior description: Version 0.0.4 of CoFlo, while usable and arguably even useful, is very much in its early stages of development.  Expect CoFlo's abilities to improve dramatically over the next several releases.

Supported Platforms

CoFlo should build and run on any POSIX platform which supports its few prerequisites listed below.  CoFlo 0.0.4 has been tested and is known to function on the following platforms:

Obtaining CoFlo

The CoFlo 0.0.4 source distribution is available from  Precompiled binaries are not available at this time.

Installing CoFlo

The CoFlo distribution is fully Autoconfiscated and installs easily.  There are few prerequisites, listed below, all of which also are easy to install.


Build Prerequisites




Runtime Prerequisites




Download the DParser 1.26 source distribution

Download the  DParser 1.26 source distribution tarball (.tar.gz format) from here and place the file somewhere outside the CoFlo source tree.  Do not untar it: the CoFlo build process will build and install the necessary static library and the "make_dparser" program under its own source tree.

Download the Boost C++ Libraries 1.48.0 source distribution

Download the Boost C++ Libraries version 1.48.0 source distribution (.tar.bz2 format) from here. and place the file somewhere outside the CoFlo source tree.  Do not untar it: the CoFlo build process will build and install the necessary libraries under its own source tree and link to them statically.

If Pre-Built Boost Libraries Are Available for, or Installed on, your Platform

Linking with system installations of Boost is not supported at this time.  CoFlo requires at least Boost version 1.47.0, which as of this writing is not commonly found in most platforms' pre-built software repositories.  Boost can be difficult to install correctly as system-wide shared objects/DLLs, and can also be difficult for programs to locate and link against, especially if multiple versions are installed.  For those reasons, CoFlo builds its own local copy of the Boost libraries it needs and links against them statically.  This will not interfere with or disturb any system installations of Boost.

Optional: Install Graphviz

It's probable that your platform has a Graphviz package available via its standard package distribution methods.  While Cygwin does not have a "Cygwin native" Graphviz available, the Windows-native version works well with CoFlo.  Download its installer from the Graphviz site here .  Download and install one of these pre-compiled binaries if possible.  If not possible, follow the instructions on the Graphviz site on how to download, build, and install Graphviz from source.

Configure, Build, and Install CoFlo

Once the above prerequisite tarballs have been downloaded, CoFlo should build and install without any problems.  Make sure you specify the absolute paths to the Boost and DParser source distributions when you invoke configure, like so:

./configure --with-boost-tarball=/absolute/path/to/boost_1_48_0.tar.bz2 --with-dparser-tarball=/absolute/path/to/d-1.26-src.tar.gz
make install
The CoFlo package has a small test suite.  After the "make" and before the "make install", it would be prudent to run this test suite with a "make check".  There should be no unexpected failures reported by the test suite (there will however be a few expected failures).

Please note that a checkout of the source from Subversion will not build as easily, since the Autoconf/Automake-generated scripts are not maintained in the source repository.  Please use the distribution tarballs.

Using CoFlo

Quick Start

CoFlo ships with a few simple test files which you can use to get started with the minimum amount of effort.  These files are located in the <coflo_root>/tests directory, where "<coflo_root>" is the path to the directory where you untarred CoFlo.  Once you've successfully built and installed CoFlo, point it at one of these files like so:

coflo.exe <coflo_root>/tests/compound_condition_1.c --cfg=main
This will generate the following textual representation of the control flow graph:

Using GCC version: 4.5.3
Parsing "../tests/loop_test_1.c"...
Building Functions...
Linking function calls...
WARNING: Unresolved function calls:
Control Flow Graph of function main:
printf( [../tests/loop_test_1.c : 30] &[../tests/loop_test_1.c : 30] "Start.\n"[0] ) <../tests/loop_test_1.c:30:8>
if() <../tests/loop_test_1.c:32:7>
printf( [../tests/loop_test_1.c : 34] &[../tests/loop_test_1.c : 34] "i = %d\n"[0], i ) <../tests/loop_test_1.c:34:9>
if() <../tests/loop_test_1.c:37:4>
if() <../tests/loop_test_1.c:39:5>
printf( [../tests/loop_test_1.c : 42] &[../tests/loop_test_1.c : 42] "i = %d\n"[0], i ) <../tests/loop_test_1.c:42:10>
if() <../tests/loop_test_1.c:44:6>
printf( [../tests/loop_test_1.c : 46] &[../tests/loop_test_1.c : 46] "here\n"[0] ) <../tests/loop_test_1.c:46:11>
printf( [../tests/loop_test_1.c : 51] &[../tests/loop_test_1.c : 51] "Finished.\n"[0] ) <../tests/loop_test_1.c:51:8>
dummy( 1, 3, 4, 5, [../tests/loop_test_1.c : 53] &[../tests/loop_test_1.c : 53] "hello"[0] ) <../tests/loop_test_1.c:53:7>
Other styles of control flow graph output, such as PNG renderings of the graph, as well as analyses CoFlo can perform, are described below.

Getting CoFlo to Parse Your Source Code

CoFlo must be able to fully parse the source files you give it, which means that any necessary command-line defines and include paths must be specified.  Do this by passing -D and -I parameters as necessary on the command line.  It is best to write a small shell script to for this purpose, like this one which allows CoFlo to process the main.c file of GNU Make 3.82 (once the GNU Make source tree has been configured):

#! /bin/sh

# Create a subdirectory in the root of the make-3.82 source tree and run this script from it.



DEFS="-DLOCALEDIR='\"'${localedir}'\"' -DLIBDIR=\"${libdir}\" -DINCLUDEDIR=\"${includedir}\" -DHAVE_CONFIG_H"

# Run CoFlo.
coflo ${DEFS} ${DEFAULT_INCLUDES} ${INCLUDES} ${TOP_SRCDIR}/main.c -O html_out/

Note that currently it is not possible to specify different -D or -I options for different source files in a single invocation of CoFlo.

Control Flow Graph Output

PNG Control Flow Graphs, Single Function

If you have the Graphviz dot program installed, you can generate control flow diagrams in PNG format.  For example, the following command line:

coflo <coflo_root>/tests/loop_test_1.c --cfg=main --cfg-fmt=img -o loop_test_1.png
...turns this code:
int main(int argc, char *argv[])
int i = 6;


while(argc > 6)
printf("i = %d\n", i);

if(argc > 1)
printf("i = %d\n", i);

if(i+argc > 7)



return 0;
...into this control flow graph:

PNG control flow graph of loop_test_1.png

Note a few things about this graph:
  1. Each node in the graph corresponds to an expression or statement in the program after it has been transformed by gcc into a three-address code form.  There is generally not a direct 1-to-1 correspondence between this and the original program text.  For example, the original code contained no explicit GOTOs, while the graph contains two.
  2. The text in each node has a simple 2-line format.  The first line indicates the node number followed by what the node represents, and the second line indicates its location in the original program text.  The locations are currently extracted from the three-address code representation generated by GCC, which doesn't always provide such information, so some of the nodes indicate "UNKNOWN:0", i.e. their location could not be determined.
  3. The elements in red are function calls which CoFlo was unable to link to their targets.  This generally indicates that the translation unit defining the called function was not passed on the command line.
  4. The nodes marked "PLACEHOLDER" are really three-address code assignment expressions.  A near-future release of CoFlo will handle and display these in a more appropriate manner.
  5. Back edges in the graph are represented as dashed lines.  The while loop in the above code induces one such back edge in the graph, as can be seen between nodes 6 and 7.
  6. To maintain navigability of the graph for certain algorithms, CoFlo introduces Impossible edges during its back edge detection phase.  One such edge can be seen between nodes 6 and 9 above.
  7. CoFlo does not yet perform much simplification of the control flow graph.  For example, all the gcc-generated jump labels (i.e. the "<D.nnnn>" nodes) and the GOTOs in the above control flow graph could potentially be eliminated with no loss of information, markedly increasing the readability of the graph.  Again, this will be addressed in a near-future release.

PNG Control Flow Graphs, All Functions

CoFlo can also generate the control flow graphs of all functions in all the source files it is given and put them on an HTML page.  Simply point it at a directory in which to put the output, like so:

coflo <coflo_root>/tests/test_source_file_1.c <coflo_root>/tests/test_source_file_2.c -O test_html
Be prepared for a lot of large PNGs!

Textual representation of Control Flow Graphs, Single Function

As shown in the Quick Start section above, CoFlo can also print the control flow graph in a textual format.  Perhaps surprisingly, properly formatting a control flow graph as indented text is quite difficult, and CoFlo is not yet able to format certain constructs correctly.  Expect to see some oddly-formatted textual control flow graphs until this is rectified.

Control Flow Graph Analysis

CoFlo is also capable of performing some analyses of the control flow graph.


As of this release, just one analysis is available, function-entry-to-function-entry reachability.  Function-entry-to-function-entry reachability works across translation units and through any number of intermediate function calls.

Reachability constraints are specified on the command line like so:

coflo <files, other args, etc.> --constraint="function1() -x function2()"

where function2() is the function which should not be reachable from function1().  The "-x" is intended to visually suggest non-navigability from the left-hand-side to the right-hand-side of the constraint specification.  Any number of constraints can be specified by simply passing as many --constraint="..." options as necessary on the command line.

Here is an example, using the "test_src_1" files from the CoFlo distribution:

$ ./src/coflo.exe ../tests/test_src_1/*.c --constraint="ThreadBody1() -x UnsafePrint()" --constraint="ThreadBody2() -x UnsafePrint()"
Using GCC version: 4.5.3
Parsing "../tests/test_src_1/Layer1.c"...
Building Functions...
Parsing "../tests/test_src_1/RarelySafePrint.c"...
Building Functions...
Parsing "../tests/test_src_1/Thread1.c"...
Building Functions...
Parsing "../tests/test_src_1/Thread2.c"...
Building Functions...
Parsing "../tests/test_src_1/ThreadUnsafeFunctions.c"...
Building Functions...
Parsing "../tests/test_src_1/main.c"...
Building Functions...
Linking function calls...
WARNING: Unresolved function calls:
INFO: Adding constraints...
INFO: Adding constraint: ThreadBody1() -x UnsafePrint()
INFO: Adding constraint: ThreadBody2() -x UnsafePrint()
Couldn't find a violation of constraint: ThreadBody1() -x UnsafePrint()
../tests/test_src_1/Thread2.c: In function ThreadBody2:
../tests/test_src_1/RarelySafePrint.c:25:13: warning: constraint violation: path exists in control flow graph to UnsafePrint( string, integer )
../tests/test_src_1/RarelySafePrint.c:25:13: warning: violating path follows
../tests/test_src_1/Thread2.c:24:2: warning: if(i <= 99), taking out edge "true"
../tests/test_src_1/Thread2.c:26:5: warning: if(arg != 0B), taking out edge "false"
../tests/test_src_1/Thread2.c:32:22: warning: SometimesSafePrint( [../tests/test_src_1/Thread2.c : 32] &[../tests/test_src_1/Thread2.c : 32] "Thread 2: "[0], i )
../tests/test_src_1/Layer1.c:28:4: warning: if(external_forces.0 != 0), taking out edge "false"
../tests/test_src_1/Layer1.c:39:18: warning: RarelySafePrint( string, integer )
../tests/test_src_1/RarelySafePrint.c:25:13: warning: UnsafePrint( string, integer )

In this example, two constraints are specified, one of which is not violated by the code and one which is.  CoFlo reports that can't find a violation of the first constraint.  For the violated constraint, CoFlo prints the path through the control flow graph which violates the constraint.  Note that it is the offending call site which is reported, even though what was actually detected was the ENTRY node of the function being called.  This is done with the idea that the call site, which contains the parameters passed to the function, is the true item of interest.

Note that this analysis is not function-to-function-call reachability - CoFlo must be able to resolve both of the functions in question or it will not detect the path. 

The effects of the actual evaluations performed by conditionals on the feasibility of the analyzed paths are not currently taken into account by this analysis.  Because of this, given a code fragment such as this:


it is possible that CoFlo will report that UnreachableFunction() is in fact reachable.

Known Issues

Version 0.0.4 is an early alpha release of CoFlo, and as such there are more known issues than it makes sense to list here.  These are a few of the major ones:

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"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
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An MMC is "eligible for relicensing" if it is licensed under this
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The operator of an MMC Site may republish an MMC contained in the site
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ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
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If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

with the Invariant Sections being LIST THEIR TITLES, with the
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If you have Invariant Sections without Cover Texts, or some other
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If your document contains nontrivial examples of program code, we
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