Can a C program modify its executable file?

Question

I had a little too much time on my hands and started wondering if I could write a self-modifying program. To that end, I wrote a \"Hello World\" in C, then used a hex editor

Answer 1

If you are using Windows, you can do the following:

Step-by-Step Example:

1. Call VirtualProtect() on the code pages you want to modify, with the PAGE_WRITECOPY protection.
2. Modify the code pages.
3. Call VirtualProtect() on the modified code pages, with the PAGE_EXECUTE protection.
4. Call FlushInstructionCache().

For more information, see How to Modify Executable Code in Memory (Archived: Aug. 2010)