Thread: Copying WHOLE Functions

I need help! What I want to do is to copy and paste the code of fucntions into an array of some sort and execute, through function pointers, the new code inside the array. (I'm not a hacker, btw). I also want to remove the return statements when copying the functions so I can add others. For example:

void a()
{
printf("hello");
}
voit b()
{
print(" world\n");
}

I want in a char array:
{ code for a minus the return statement, code for b normally }

Then with a function pointer to that array, I can hopefully execute the new combined code.

So say we have:

void m()
{
printf("HELLO!\n");
}
void f() { }

.....
// no casting is done here for reading's sake
char *s=new char[1000];
memcpy(s, &m, &f-&m);
void (*go)(void)=s;
go();
// prints out "HELLO"
...


I would want to do all this in a class too (like the functions being member functions).

HELP ME! HOW TO DO?

I bet you advanced coders know how to do all this, LOL!

I want to clone the function, take it's code at runtime through pointers and copy it all into an array. And by trimming off X-number of bytes at the end (the assembler 'ret'), we can prevent the copied function from returning so I can paste another afterwards. I just want to have some help on this.

I'm not a hacker, I'm not stupid. But please help!

Its for a VERY VERY primitive form of a JIT Compiler.

(This board responds fast, lol)

basically, i just want to test myself on this

I can know the size of the function. Test it out. I put the f() function as a barrior. I take the address of f() and minus it from m(). That gives me, usually (works on Retail build), the correct size of the function.

Where i got this idea:

POSTED ON PLANET SOURCE CODE C++ SECTION




#include <stdio.h>
#include <stdlib.h>
#include <string.h>


/* This programs shows how to copy the bytecodes of a function to a variable
then execute this chunk of code (dynamic linking?). Not sure if this works
with all compilers and all machines/OSes
*/

int func1 (int a, int b){ /* this is the function that will be copied */
int i;
for (i=0;i<=100;i++){ /*some silly code.. doesnt have to do with the purpose of this program */
a+=i + b;
}
return a;
}
void func2(){ /*this useless function is declared to mark a boundary */
} /* its address is just after the code for func1 */

int (* f) (int a, int b); /*a function pointer, must have the same args of the copy*/

int main(){
/*try
{*/
int *start,len,i,*end;
char * funccopy;
start = (int* ) &func1 ; /*where to start copying? */
end = (int* ) &func2; /* to determine length of char array to copy*/
len = end-start; /* */
funccopy = (char *)malloc (len);
printf ("length of bytecode buffer %d\n",len); /* if you change the code within func1 you will see this number change accordingly */
memcpy (funccopy,(void *)start,len); /*^ an easy way to determine the speed of your functions! */
f = (int(__cdecl*)(int,int)) funccopy; /*now f will point to our copy */
printf ("Value %d\n", f (3,4)); /* test it... does it work? */
/*}
catch (...)
{
printf("DAMN");
}*/

system("pause");
return 0;
}

You are right, I can't be sure. BUT, as I said, on the Retail build, it works, (the function size). I am SURE of this.