Table of contents


LeakTracer is a small tool I wrote when checking a C++ program for memory
leaks. I couldn't get dmalloc to display what I wanted, and I just saw the
__builtin_return_address gcc-extension mentioned.

To use LeakTracer, run your program using the provided LeakCheck script. It
uses the LD_PRELOAD feature to "overlay" some functions on top of your
functions (no recompile needed). If your platform does not support LD_PRELOAD,
you can add the LeakTracer.o object file to the objects in your Makefile and
run your application. 

LeakTracer uses gdb to print out the exact line where the memory was allocated
and not freed - this of course means you have to free all dynamically
allocated data. LeakTracer also overrides the global operator new and operator
delete - this will give problems if you override them as well.

LeakTracer traces only new/new[] and delete calls - it does not look at

Here is some example output:

Gathered 8 (8 unique) points of data.
Allocations: 1 / Size: 36
0x80608e6 is in NullArcableInstance::NullArcableInstance(void) (
39      public:
40          NullArcableInstance() : ArcableInstance(new NullArcable) {}

Allocations: 1 / Size: 8
0x8055b02 is in init_types(void) (
118     void init_types() {
119         Type::Integer = new IntegerType;

Allocations: 1 / Size: 132 (new[])
0x805f4ab is in Hashtable::Hashtable(unsigned int) (ea/h/Hashtable.h:15).
14          Hashtable (uint _size = 32) : size(_size), count(0) {
15              table = new List [size];



You need Perl5 and gdb installed to run the leak-analyzer. You need gcc -- I
currently use 2.95 but have used it with previous older versions without
You also need to run this on an architecture which supports
__builtin_return_address arguments that are greater than 0 - there may be
some problems on MIPS there. 

So far this code has been tested under Linux 2.2, x86 system, Solaris and


Just type make. There is no install target; you should put LeakTracer
some place you can remember.

Since version 2.0, it is possible to preload the LeakTracer object on
architectures that support LD_PRELOAD (this is at least Linux and probably
others -- please report success/failure). This means it is much easier to use
the program: you do not need to relink your program with LeakTracer.o.

In case your platform does not support LD_PRELOAD, you can use LeakTracer in
the old pre 2.0 way: add LeakTracer.o to your object files -- at the very end
of them (also after -llibrary lines).

In any case your application must also be compiled with debugging enabled
(i.e. -g).

Running with LeakTracer

If you are using the shared object, run the LeakCheck script. This script
should stay in the directory where you install LeakCheck -- it will search for file there and load it. E.g.:

~/src/LeakTracer/LeakCheck yourApplication

(if you put LeakTracer in ~/src/LeakTracer/)

Run your application as normal, performing tasks that you want to be traced
for memory leaks. While the application runs, LeakTracer will write data about
memory allocation to the file "leak.out" in the current directory. You can
override the location of that file by setting the LEAKTRACE_FILE environment

If you cannot use LD_PRELOAD, just run your application as normal after
relinking it. It will also produce a "leak.out" file when it finishes.

Detectable errors

LeakTracer is capable to detect the following problems with your program

  1) memory which is allocated but not freed
  2) (limited support for) overwritten memory at the end of the allocated
     block  ( reason = 1 )
  3) memory which is tried to be deleted but which is not allocated
     (either because of a garbage pointer or twice deletion)
     (reason = 2)
  4) memory which is allocated with new[] but deleted with simple delete
     and vice versa (reason = 4)

For the last three problems, LeakTracer can abort() your program if you
tell it so; the resulting core-dump allows to debug the problem. By default,
only the overwrite memory condition results in an abort of the program
because it is inherently critical. The two other conditions are not critical.
You can influence what LeakTracer does with the environment variable
which you can set to some numeric value which is the result of the
sum of the reasons you find in the parentesis in the enumeration above.
To abort on any reason, for example, you would set LT_ABORTREASON to 7.

Analyzing output

You should then run leak-analyze, since looking at the raw leak.out file will
not help you much. To run leak-analyze, you need Perl as well as gdb
installed (any version of gdb will do). For example:

leak-analyze myprog leak.out

You don't have to specify the leak.out filename if you just use the default
one. leak-analyze will run gdb on the file, sending it a number of commands
that will show the source lines with the memory leaks.

leak-analyze should show you something like this:

Gathered 2 (2 unique) points of data.

#-- Alloc: Different allocation schemes
alloc here :0x80485b7 is in main (
6               int *wrong = new int[10]; here :0x80485d9 is in main (
11              delete wrong;

#-- Leak: Allocations: 1 / Size: 168 
0x8048593 is in main (
2       int main() {
3               int *array = new int [42] ;

#-- Leak: Allocations: 1 / Size: 4 
0x80485a5 is in main (
3               int *array = new int [42] ;
4               int *foo = new int;
This means that total of two allocations happened, in two different places.

First a delete error is shown: you allocated some memory using new[] but you
freed it using delete. leak-analyze will show where you allocated the memory and where you freed it.

Afterwards each allocation is shown in turn. There was 1 allocation from this
line of code (, and it was 168 bytes in size. Note that of the two
lines of code shown, it's the bottom one that created the allocation.

That's all there is to it - now you should find those memory leaks, fix them
and rerun Leak tracer.

Shared libraries and objects

If you want to analyze the leaks in shared libraries in your file, it may be
necessary to make leak-analyze run your program and thus load the shared
libraries before searching for addresses.

To do that, run leak-analyze with the program name, leak name AND another
argument which is where to set the breakpoint, e.g.:

leak-analyze myprog leak.out main

This will make leak-analyze tell gdb to set a breakpoint on "main" and then
run the program. After the analysis is complete, the program will be killed.

If you want to load some shared libraries, you can set a breakpoint on a
different location, e.g. if you know that once line 42 is reached,
all shared objects have been loaded.

If your program needs some command line arguments, supply them after "main".


LeakTracer is public domain (i.e. do with it whatever you feel like).


Initial version of LeakTracer was written by Erwin Andreasen. Henner Zeller
( contributed a rewrite of the code which
introduced dynamic loading of LeakTracer and more.

Revision history

February 21, 1999       v1.0 - only tested internally
February 23, 1999       v1.1 - added operator new[] / delete[]
February 23, 1999           v1.2 - Oops, forgot to free() the memory..
February 26, 1999       v1.3 - allow delete 0
March 27, 1999          v1.4 - Allow %p format without leading 0x for non-GNU 
                                       libc. Option to leak-analyze to run the program.
July 21, 1999               v1.5 - Fix for the above suggested by Alan Gonzalez
August 21, 2000         v1.6 - use a destructor instead of 
November 19, 2000               v2.0 - Rewrite by Henner Zeller introduces LD_PRELOAD
                                       and much more
February 27, 2001               v2.1 - Further update by Henner: optional thread safety,
                                       choose what should make LeakTracer abort(), better
                                       tracing of delete on non-new'ed pointers
March 2, 2001                   v2.2 - Another updated by Henner: hash table to increase
                                       performance with many allocations
June 13, 2001                   v2.3 - Made LT more resistant to being called before init
                                       and after destruction
August 28, 2003                 v2.4 - Improve MAGIC on platforms that don't allow unaligned

Authors:    Erwin Andreasen 
        Henner Zeller