Thread: Changing symbol's linkage

Is there a way to "overload" the symbols of a binary? For example, I compiled my application and sent it to user. He is running it, but he discovers that the application randomly crashes. I suspect that is a memory leak problem, but I can't reproduce the problem myself. I would like the binary to, at execution time use the malloc from a library that I would provide, instead of C malloc. You could argue that I should use Valgrind for a memory leak problem (and I would), but this is just an example of what I want to do. Actually I would like to manage many resources, just to keep trace of them, like file descriptors.

My target platform is Linux, compiling with GCC. The project is also ported to GCC on Windows.

Thanks any help or dirctions, I will gladly specify better my problem if needed.

Write a small module with your implementation of malloc(). Compile with -fPIC option and turn it into a shared library:

Code:

$ gcc -fPIC -c my_malloc.c
$ ld -shared -o libmy_malloc.so my_malloc.o -lc

Send it to the user and have him give the command:

Code:

export LD_PRELOAD=libmy_malloc.so

This will override the standard library malloc() with your own. It will override it for ALL programs he runs after that point, at least in that shell.

Of course, you probably want your override malloc() to call the built-in malloc() at some point. You can refer to it in your stub code as __libc_malloc() (double underscore at front)

Thanks so much!