Interpositioning Case Study
David O'Hallaron, Carnegie Mellon University

This directory illustrates three different techniques (run-time,
link-time, and compile-time library interpositioning) for intercepting
and wrapping library functions such as malloc and free.

The example program (int.c) calls malloc and free:

#include <stdio.h>
#include <malloc.h>

int main()
{
    int *p = malloc(32);
    free(p);
    return(0); 
}

The objective is to interpose our own wrapper functions for malloc and
free that generate a trace of the sizes and locations of the allocated
and freed blocks. We can accomplish this using three different
techniques:

1. Run-time interpositioning using the dynamic linker's LD_PRELOAD
mechanism.

To build: make intr
To run: make runr

2. Link-time interpositioning using the static linker's (ld) "--wrap
symbol" flag.

To build: make intl
To run: make runl
	
3. Compile-time interpositioning using the C preprocessor.

To build: make intc
To run: make runc

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Files:
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Makefile
int.c		main routine
intc*		executable based on compile-time interposition
intl*		executable based on link-time interposition
intr*		executable based on run-time interposition
malloc.h	header file for compile-time interposition
mymalloc.c	contains source for all three interposition examples
mymalloc.o	relocatable object file for link-time interposition
mymalloc.so*	shared library file for run-time interposition