The code you are writing "c3" is actually a xor gs:[something] command which dies because [something] isn't a valid pointer.
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Question
opcode generation and execution
I'm trying to write a program that generates some opcodes and then executes them.
I can't seem to get it to work what is wrong?
it dies saying the address at the memory location pointed to by p could not be read
Here is what I've got:
#include <stdio.h>
#include <windows.h>
void (*func)();
int main()
{
void *p;
char *pc;
printf("hello\n");
// allocate the memory
p = VirtualAlloc(NULL,1024,MEM
if (p == NULL)
printf("virtual alloc failed");
else
{
// write the opcodes to the memory
pc = p;
// ret = c3 ?? right ??
(*pc) = 12; // c
pc++;
(*pc) = 3; // 3
pc++;
// call the function
func = p;
func();
// all done
printf("done\n");
}
}
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Answers
One at a time:
yes I should do a 0xc3 as a single byte
I use a ret to return from the function.
basically what I'm tyring to do is to create a function in machine code execute it and have it return. later it will do more complicated stuff
I'm still new at translating assembly code to machine code but I thought ret was 0xc3 if not then is there where do you recommed I look for the proper value? I got c3 from the intel docs (.pdf) but I may have misread them.
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by: WxWPosted on 2003-07-08 at 14:27:11ID: 8880663
obvious error
ret = 0xc3 , not "c3"
*pc = 0xc3 is what you need.
But why issuing a ret command there ?