This is a binary executable file debugging tools. Can be used for debugging the compiled binaries or third-party binary dynamic or static library file. This tool is used to modify, redirect function import. Can also be used to monitor function calls or Redefining Function.
As in the following sample code:

// hello.c
#include "stdio.h"

int main(int argc, char *argv[])
{
printf("Hello World!\n", argc);
return 0;
}

Execute the following command line to compile the source file:
$gcc hello.c -o hello
Will generate named "hello" executable file, run the "hello" will be displayed: Hello World!
Open this tool in the tool to open "hello", you will see hello called "/usr/lib/libSystem.B.dylib" in the "printf" function to display this text.
See figure:

When debugging software, sometimes want to know what the procedure "printf" to pass those parameters, or want to call your own "printf".
First, we have to write their own "printf" function:

// print1.c
#include "stdio.h"

int print1(const char *format, ...)
{
printf("Call Printf: format=%s\n", format);
return 0;
}

Execute the following command line to compile the source file:
$gcc -dynamiclib print1.c -o print1.dylib
Will generate "print1.dylib" dynamic libraries.
This example would call the system "printf" function, so we will own "printf" function named "print1".
In this tool to import "print1.dylib". See figure:


Modify "_printf" as "_print1", select from "print1.dylib" import this function. See figure:


Click "Apply" to save the changes. See figure:


Save as "hello[1]".
Run "hello[1]", will get the following results:
$./hello[1]
Call Printf: format = Hello World!

Please refer to this address:
http://www.vmeisoft.com/spy/readme/