codeviz

by petersenna

petersenna /codeviz

CodeViz: A CallGraph Visualiser

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WHERE DOES THIS CONTENT COMES FROM?

The website of codeviz was down today and It was difficult to find the source code for download. I used:

https://web.archive.org/web/20150502053825/http://www.csn.ul.ie/~mel/projects/codeviz/#download

to find and download the source code you see here. The only change I made was adding this header to this file.

README

This is the README for the CodeViz set of scripts. The tools are for the creation of call graphs for C and C++ so that function flow can be visualised. They are licensed under the GPL, see the COPYING file for details.

Introduction

At some stage in everyone's programming career, they will need to read through a lot of code written by another programmer. An important part of program comprehension is building a picture of how the program is structured from a high-level view and call graphs can be an invaluable aid when building this piecture. This is particularly useful if the original programmer uses clear function names.

This project provides the ability to generate call graphs to aid the task of understanding code. It uses a highly modular set of collection methods and can be adapted to support any language although only C and C++ are currently supported. Each collection method has different advantages and disadvantages.

Installing

cd codeviz cp ./lib/* -rv /usr/lib/ (Or your preferred perl library path) cp ./bin/* /usr/local/bin

Alternatively just run the scripts directly from the package bin/ directory as the libraries can be found as long as the libs are installed in a global perl directory or at the lib/ directory is the same level as bin/.

The graphs are rendered using dot which is part of the GraphViz project. Install the package for your distribution or obtain it directly from http://www.graphviz.org

Scripts

genfull - Use this to generate the full call graph for a project. This will be quite large and probably should be pared down with gengraph. A number of collection methods are available but cdepn is the default. Run genfull --man to get a full man page. Do not bother putting the output full.graph through dot yourself as it is unlikely to be rendered within a reasonable amount of time

gengraph - This will generate a small subgraph and postscript file for a given set of functions. Run gengraph --man for full details

Generating cdepn Files for genfull

If the full.graph for the source you are interested in have already been created, you can skip this section. See ./graphs to see if a full.graph is available.

The cobjdump and cppobjdump (for C and C++ respectively) will generate adequate call graphs but the information is a bit lacking. For example, the source file of a function declaration is unknown and macros and inline functions will be totally missing. Ideally, the cdepn method should be used but it requires a patched version of gcc and g++ to work. The patches and some scripts are available in the compilers/ directory.

The patched version of gcc and g++ outputs .cdepn files for every c and c++ file compiled. This .cdepn file contains information such as when functions are called, where they are declared and so on. Earlier versions of CodeViz supported multiple gcc versions but this one only support 7.4.0.

First, the source tar has to be downloaded. For those who have better things to do than read the gcc install doc, just do the following

cd compilers ncftpget ftp://ftp.gnu.org/pub/gnu/gcc/gcc-7.4.0/gcc-7.4.0.tar.gz ./install_gcc-7.4.0.sh

This script will untar gcc, patch it and install it to the supplied path. If no path is given, it'll be installed to $HOME/gcc-graph . I usually install it to /usr/local/gcc-graph with

./install_gcc-7.4.0.sh /usr/local/gcc-graph

If you seriously want to patch by hand, just read the script as it goes through each of the steps one at a time. There is one step to note though.

For now, we will presume a patched version of gcc and g++ is now in $HOME/gcc-graph/. Most projects will use the variable CC for deciding which version of gcc to use. The handiest way to use the patched one is with something like

make CC=$HOME/gcc-graph/bin/gcc CXX=$HOME/gcc-graph/bin/g++

Or alternatively, adjust your path that gcc-graph will appear before the normal gcc. As each source file is compiled, the corresponding cdepn file will be created.

In the case of building the Linux Kernel, the commands would be;

make CC=$HOME/gcc-graph/bin/gcc bzImage make CC=$HOME/gcc-graph/bin/gcc modules

Similar methods will work for other projects presuming that the Makefile uses the CC or CXX macros correctly to indicate the compiler to use. If it's a Makefile of your own type or it does not use proper macros, you may have to edit the Makefile yourself or else adjust your path to put gcc-graph first. For example, with bash, the following will work.

PATH=$HOME/gcc-graph/bin:$PATH

When building, watch the compiler output to make sure the .cdepn files are being created.

Generating nccout files for genfull

An alternative to using a patched version of gcc is to use ncc (http://freshmeat.net/projects/ncc) which is a C compiler specifically designed for code browsing. It comes with it's own navigation tool and is well worth checking out.

CodeViz supports ncc with the cncc collection method (just like cdepn is for use with gcc) and supports C only. The really big thing going for the ncc collection method is that it can traverse function pointers. If you download and install ncc, use the cncc collection method if it is C code and function pointers are common.

Once ncc is installed, in the case of building the Linux Kernel, the commands would be:

make -i CC='ncc -ncoo -ncfabs' bzImage make -i CC='ncc -ncoo -ncfabs' modules find . -name *.nccout | xargs cat > code.map.nccout

Generating full.graph

Some full.graph files are provided with the tar in the downloads section. If one you want is not available, read on.

To create a full.graph, the script genfull is used. run genfull --help to see all options but the easiest thing to do is run the script with no arguments in the top level source directory after a compile and a file full.graph will be created in the top level source directory.

While it should be possible to put full.graph though dot and see the postscript file, it is recommended you do not try. A full graph is extremely large and unlikely to be rendered in a reasonable amount of time. One really should use the gengraph program to create smaller graphs.

Problems that might exist with full.graph

In more complex code, the full.graph may not be perfect. For example, there may be naming collisions where there is duplicate function names between modules or if there is multiple binaries being compiled, genfull will not distinguish between them. If you think this will be a problem, there is two steps you can make.

First, compare the graph generated by cdepn with the one generated by cobjdump. As cobjdump is analysing a binary, it is highly unlikely the graph is wrong, it just will have no information on inline functions or macros. With the linux kernel, this test would look something like

genfull -g cobjdump -o full.graph-objdump genfull -g cdepn -o full.graph-cdepn gengraph -t -d 5 -g full.graph-objdump -f kswapd -o kswapd-objdump.ps gengraph -t -d 5 -g full.graph-cdepn -f kswapd -o kswapd-cdepn.ps

This would generate two full.graphs and two call graphs of the function kswapd() which could be compared to make sure the cdepn graph is accurate. A similar method can be used for other projects.

The second problem that may occur is where function names are duplicated between modules. In this case, the best course of action is to use the -s switch to genfull to limit which branches of the tree are examined. For example, in the linux kernel there is an alloc_pages() function in mm/ and drivers/char/drm . If one was examining the VM alone and naming collisions were expected to be a problem, genfull could be invoked as

genfull -s "mm include/linux drivers/block arch/i386"

which would cover most of the functions of interest. In other projects, it will be a case of different libraries colliding with each other. For instance, with avifile, genfull with no arguments will create a horrible mess. Instead, the -s switch must be used to generate a full.graph for each part of the project. For example, the player would be graphed with

genfull -s "player" -o full.graph-player

and each of the libraries would be graphed separately.

Generating Call Graphs

The script gengraph generates a call graph for a specified function based on the full.graph file. gengraph --man will provide all the information you need. The most important switch to note is -g which determines what collection method to use. Once the script completes, a postscript file will be available which can be viewed with any postscript viewer. By default, the output filename will be functionname.ps

If it takes a long time to generate a graph, it is usually a good idea to first limit it's depth to something reasonable with -d . We'll take an example of graphing alloc_pages() with kernel 2.4.20

Step 1: gengraph -f alloc_pages Result: Taking way too long, hit ctrl-c and limited by some reasonable depth to get an idea of what was happening

Step 2: gengraph -d 10 -f allocpages Result: Output graph is massive, mainly with kernel stock functions of no interest. Use the -t switch to omit functions that are usually of no interest. For other projects, edit the gengraph script and go to the line "sub generatetrimlist", this function has a list of functions to "trim" with the -t switch is used

Step 3: gengraph -t -d 10 -f allocpages Result: Output graph is still massive but a glance at the graph shows that a call to "shrinkcache()" is resulting in a massive graph below it that does not look like it is directly related to page allocation. Lets just show that function but not traverse it with the -s switch

Step 4: gengraph -t -d 10 -s "shrinkcache" -f allocpages Result: Graph size is drastically reduced. Most of the remaining graph involves two functions "trytofreepageszone()" and "_freepagesok". We'll not traverse trytofreepageszone() and will ignore _freepagesok() altogether with the -i switch

Step 5: gengraph -t -d 10 -s "shrinkcache trytofreepageszone" -i "freepagesok" -f allocpages Result: Perfect, shows a nice graph which clearly shows what the important functions are in relation to just page allocation. Later the branches that were not traversed in this graph can be graphed separately

The bottom line is that the first graph is usually too large and needs to be cut down. How to pare it down in a combination of experience with the code and common sense. I find it usually helps to just limit the depth first by 4 and start ignoring functions that are obviously not of current interest and traverse them later

Generating Graphs based on Regular Expressions

Support is available for selecting functions to graph, show and ignore based on regular expressions. The format of the expression is the same as perl except without the //'s. For example, to generate a graph that d that look like an alloc function in the kernel, this would work

gengraph -t -d 4 --func-re "^.?.?alloc(page)?$" -i "pmdalloc" -o allocs.ps

Note that with --func-re in particular, it is important that you use the -o switch or dot will fail to create a graph with complaints about bad output filenames.

Post-Processing Options

Both genfull and gengraph support the use of post-procesing steps. Currently, two are supported. The first is stack usage by a single function. This is x86 specific as it depends on object files regardless of the collection method used. This is mainly of benefit to the Linux kernel as normal applications can expand their stack and do not need to worry about stack usage as much. The second module shows cumulative usage in gengraph between pairs of functions. This is really handy for showing the usage between a system call and a lower-level function to identify places where stack is used too much.

See the man pages for genfull and gengraph for more information on the use of the post-processing options.

Daemon/Client Support

With a large input graph, the longest operation for the generation of the call graph is the reading of the input file. To compare, to generate a small graph on the authors machine, it takes 4 seconds to read the input graph and 0.1 seconds to generate the output file. To address, this, gengraph can run as a daemon if the -q (--daemon) switch is specified. Use -v if you want to see what it is doing.

gengraph -q -g /usr/src/linux-2.4.20-clean/full.graph

When this returns, the daemon is running. To generate a graph using the daemon, run gengraph -q -t -d 2 -f alloc_pages

Note the use of the -q switch which says that gengraph should run as a client to the daemon instance. If you are bored, compare the difference in running times between normal gengraph and when it is used as a client :-) . To stop the daemon, do the following

echo QUIT > /tmp/codeviz.pipe

and the daemon will shutdown and cleanup.

Generating Graphs for the Web

Gengraph is now suitable for use with CGI scripts. To generate GIF output instead of postfix, use the -w switch. How you choose to implement is up to yourself but what I did was the following

o Have CGI script call gengraph to output GIF to /tmp o In the HTML, have

Where output.gif is actually some temporary file in /tmp created by the CGI script with a unique name and readgif is a simply exectuable which reads GIFs from /tmp and then unlinks them.

There is no demo of this available because the webserver which hosts this project is a bit loaded. While I could run a demo, my popularity would take a bit of a dent.

There is also support for generating HTML files with source-highlight if you have it installed. See the detailed manpage for the --shighlight option for more details.

Misc Notes

Reports of success or failure, especially with C++, using any of the collection methods are appreciated.

Bugs and Feedback

Email any comments, feedback and bug reports to [email protected] Enjoy.....

Credits

The vast majority of this has been implemented by Mel Gorman [email protected]. However, the diff to gcc and original cdepn.pl that this project was originally based on was written by Martin Devera (Devik) (http://luxik.cdi.cz/~devik). They have since changed considerably to support other languages and be more flexible but the original idea was his, thanks Martin. Encouragement and prodding to support ncc is courtesy of the author of ncc Xanthakis Stelios ([email protected]). The main guts of the implementation of the regular expression support and HTML rendering is courtesy of Robert Lehr ([email protected]).

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