Can I load a library from a memory stream?

Question

Can I load a library from a memory stream? For example my library is encoded a file. I check some conditions and decrypt the file into a memory stream. Now I need to load the decrypted library from that stream into my application and use its functions etc.

Answer 1

In windows, A DLL can only be loaded from a file - as the links suggested, you can create a ramdisk and install that as a drive, but there is no way around the DLL needing to be loading through an file that exists in a filesystem. Part of the reason for this is that the DLL is "demand loaded", that is the system does not load the entire file into memory at once, it loads the parts that are actually being used, 4KB (typically) at a time. It is also not swapped out to the swap area, it is just discarded and re-loaded from the DLL if the system is running short of memory.

Linux works in a very similar way (I know it uses the same kind of demand-loading by default, but not sure if there is a way around it), so I don't believe there is any other way there either, but I haven't looked into it at depth.

Of course, if all you want is a piece of code that you can use in your application, and you want to store that as encrypted/compressed/whatever in your exectuable file, what you can do is allocate some executable memory (in Windows, you can use VirtualAlloc to allocate executable memory). However, you need to ensure that you relocate any absolute memory addresses in your code if you do that, so you will need to store the relocation information in your executable.

Clearly, the easy solution is to unpack your content into a file in the filesystem, and load from there.