Make an executable at runtime

Question

Ok, so I was wondering how one would go about creating a program, that creates a second program(Like how most compression programs can create self extracting self excutables, but that's not what I need).

Say I have 2 programs. Each one containing a class. The one program I would use to modify and fill the class with data. The second file would be a program that also had the class, but empty, and it's only purpose is to access this data in a specific way. I don't know, I'm thinking if the specific class were serialized and then "injected" into the second file. But how would one be able to do that? I've found modifying files that were already compiled fascinating, though I've never been able to make changes that didn't cause errors.

That's just a thought. I don't know what the solution would be, that's just something that crossed my mind.

I'd prefer some information in say c or c++ that's cross-platform. The only other language I'd accept is c#.

also

I'm not looking for 3-rd party library's, or things such as Boost. If anything a shove in the right direction could be all I need.

++also

I don't want to be using a compiler.

Jalf actually read what I wrote

That's exactly what I would like to know how to do. I think that's fairly obvious by what I asked above. I said nothing about compiling the files, or scripting.

QUOTE "I've found modifying files that were already compiled fascinating"

Please read and understand the question first before posting.

thanks.

Answer 1

Ok, so I was wondering how one would go about creating a program, that creates a second program

You can look at CodeDom. Here is a tutorial

Answer 2

Invoke a compiler with data generated by your program (write temp files to disk if necessary) and or stored on disk?

Or is the question about the details of writing the local executable format?

Answer 3

Unfortunately with compiled languages such as C, C++, Java, or C#, you won't be able to just ``run'' new code at runtime, like you can do in interpreted languages like PHP, Perl, and ECMAscript. The code has to be compiled first, and for that you will need a compiler. There's no getting around this.

If you need to duplicate the save/restore functionality between two separate EXEs, then your best bet is to create a static library shared between the two programs, or a DLL shared between the two programs. That way, you write that code once and it's able to be used by as many programs as you want.

On the other hand, if you're really running into a scenario like this, my main question is, What are you trying to accomplish with this? Even in languages that support things like eval(), self modifying code is usually some of the nastiest and bug-riddled stuff you're going to find. It's worse even than a program written completely with GOTOs. There are uses for self modifying code like this, but 99% of the time it's the wrong approach to take.

Hope that helps :)

Answer 4

Building an executable from scratch is hard. First, you'd need to generate machine code for what the program would do, and then you need to encapsulate such code in an executable file. That's overkill unless you want to write a compiler for a language.

These utilities that generate a self-extracting executable don't really make the executable from scratch. They have the executable pre-generated, and the data file is just appended to the end of it. Since the Windows executable format allows you to put data at the end of the file, caring only for the "real executable" part (the exe header tells how big it is - the rest is ignored).

For instance, try to generate two self-extracting zip, and do a binary diff on them. You'll see their first X KBytes are exactly the same, what changes is the rest, which is not an executable at all, it's just data. When the file is executed, it looks what is found at the end of the file (the data) and unzips it.

Take a look at the wikipedia entry, go to the external links section to dig deeper: http://en.wikipedia.org/wiki/Portable_Executable

I only mentioned Windows here but the same principles apply to Linux. But don't expect to have cross-platform results, you'll have to re-implement it to each platform. I couldn't imagine something that's more platform-dependent than the executable file. Even if you use C# you'll have to generate the native stub, which is different if you're running on Windows (under .net) or Linux (under Mono).

Answer 5

Have you considered embedding a scripting language such as Lua or Python into your app? This will give you the ability to dynamically generate and execute code at runtime.

From wikipedia:

Dynamic programming language is a term used broadly in computer science to describe a class of high-level programming languages that execute at runtime many common behaviors that other languages might perform during compilation, if at all. These behaviors could include extension of the program, by adding new code, by extending objects and definitions, or by modifying the type system, all during program execution. These behaviors can be emulated in nearly any language of sufficient complexity, but dynamic languages provide direct tools to make use of them.

Answer 6

Depending on what you call a program, Self-modifying code may do the trick.

Basically, you write code somewhere in memory as if it were plain data, and you call it. Usually it's a bad idea, but it's quite fun.