Description Roland Grunberg 2010-07-28 09:12:55 EDT

Suppose we wanted a better understanding of how a C/C++ program "operates".
What methods are called, in what order, by which functions, etc. A visual
representation of a program's call hierarchy could probably achieve this
reasonably well, and it would be nice to have an Eclipse plugin that could
do this. Similar to an ER model being generated given a database schema.

One such way of doing this is by compiling each of the program's source files
using gcc's -fdump-rtl-<pass> flag. (For more information on flags, see the
gcc manual). This dumps debugging information during the specified pass of
compilation. RTL (Register Transfer Language) is just a format (similar to
LISP lists) that describes the various instructions performed by the CPU.

As an example, we can take the source code for Systemtap, and add the
following line to configure.ac :

CFLAGS="-fdump-rtl-expand $CFLAGS"

This will compile all C source files with the -fdump-rtl-expand flag,
which dumps the debugging information after RTL generation.

After compiling the project (./configure && make) we can grab all the
debugging data files that have been generated and pass them to 'egypt'.

Egypt (http://www.gson.org/egypt/) is a program that takes RTL data and
converts it to DOT language (http://en.wikipedia.org/wiki/DOT_language).
From this point we can pass the DOT language data to a graph generator
provided by the Graphviz Package (http://www.graphviz.org/).

cat *.expand | egypt | dot -Tjpg -o stap_egypt.jpg

This would produce something as follows :

http://rgrunber.fedorapeople.org/stap_egypt.jpg
http://rgrunber.fedorapeople.org/stap_egypt.svg

However, since our goal would be to have this be an Eclipse plugin, a
graphics library such as GEF / ZEST (http://www.eclipse.org/gef/)
would have to be used to achieve the rendering.

Drawbacks :

Large programs with many functions (nodes) can be difficult to render by
egypt. Coming up with some algorithm to do this with the GEF/ZEST libraries
would be challenging. As an example, the compilation of Systemtap was done
only with -fdump-rtl-expand for the C source files because doing it for C++
as well produced a graph that was not possible to render in most formats and
very confusing to visualize.

Other possibilities for visualizing call hierarchy are discussed below :

http://nion.modprobe.de/blog/archives/556-creating-dynamic-function-call-graphs.html
http://www.ibm.com/developerworks/library/l-graphvis/