Executing machine code in memory

Question

I\'m trying to figure out how to execute machine code stored in memory.

I have the following code:

#include 
#include          


        

Answer 1

What you are trying to do is something akin to what interpreters do. Except that an interpreter reads a program written in an interpreted language like Python, compiles that code on the fly, puts executable code in memory and then executes it.

You may want to read more about just-in-time compilation too:

Just in time compilation
Java HotSpot JIT runtime

There are libraries available for JIT code generation such as the GNU lightning and libJIT, if you are interested. You'd have to do a lot more than just reading from file and trying to execute code, though. An example usage scenario will be:

1. Read a program written in a scripting-language (maybe your own).
2. Parse and compile the source into an intermediate language understood by the JIT library.
3. Use the JIT library to generate code for this intermediate representation, for your target platform's CPU.
4. Execute the JIT generated code.

And for executing the code you'd have to use techniques such as using mmap() to map the executable code into the process's address space, marking that page executable and jumping to that piece of memory. It's more complicated than this, but its a good start in order to understand what's going on beneath all those interpreters of scripting languages such as Python, Ruby etc.

The online version of the book "Linkers and Loaders" will give you more information about object file formats, what goes on behind the scenes when you execute a program, the roles of the linkers and loaders and so on. It's a very good read.