Intercepting LibC function calls, is it possible?

Question

I have a dynamic library (no source code available) coming from a supplier. This library is linked against the uCLibC.

If I link my application against this library, can I intercept some calls that this library maybe doing to uclibc/libc (e.g. malloc, printf, ...)? For example, I would like to modify the printf that this library is using.

thanks.

See e.g. [this question and its answers](http://stackoverflow.com/questions/426230/what-is-the-ld-preload-trick). — Some programmer dude, Jun 24 '14 at 09:53
@someuser `#define printf my_printf` will not work because the OP doesn't have access to library source code to recompile it with such a `#define`. — user4815162342, Jun 24 '14 at 10:01

score 3 · Answer 1 · answered Jun 24 '14 at 10:23

3

You can use LD_PRELOAD to load a library that you wrote before libc. This way you can intercept printf, malloc, etc.

Here is a simple tutorial/example: http://www.catonmat.net/blog/simple-ld-preload-tutorial/

answered Jun 24 '14 at 10:23

Akhi

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Intercepting LibC function calls, is it possible?

1 Answers1