This is a practice to override a call to the function from library by the developer's own implementation. Dedicated to add monitoring and/or debugging stuff into functions like malloc().
This is a practice reached by features of dynamic linker to override a call in the application to the function from library by the developer's own implementation. Such mechanism is dedicated to add monitoring and/or debugging stuff into functions like malloc(), realloc(), free().
GNU linker ld allows to do that thanks to the LD_PRELOAD environment variable, which cause the indicated ELF dynamic library to be loaded prior to other libraries linked with the application being executed.
