Delay-Loaded Dlls

Something I love of using several similar (sometimes competing) technologies (C#-Java, Windows-Linux...) is that ever that I learn something new in one of them I try to find how it's done in its counterpart.

Some days ago I came across Delay-Loaded Dlls in native Windows applications. It's sort of a middle ground between the 2 normal dll loading techniques, that is:

• The most common/obvious case: statically Linked Dlls. When you compile your application references to those dlls that it needs get added to the Import Table of your PE. As soon as your Application is loaded these dlls will get loaded into its address space, irrespective of whether they'll end up being used in that particular execution.
• Dynamically Loaded Dlls. In this case the Dll is not loaded when the application starts, but you decide dynamically not only when, but also what, to load (you can decide to load one or another dll based on runtime conditions). This is all done with the LoadLibrary and GetProcAddress Win32 functions.

As I've said, Delay-loaded Dlls are something in between supported by our cute linker. You have to know at compile time the name of the Dll that you'll be delay-loading and it'll be added to the Import Table, but it won't be loaded until one of its functions is used for the first time. This means that it's like a transparent lazy version of the first case described above. Indeed, this is very similar to how .Net applications load assemblies "statically" (I mean, not using Assembly.Load...). The Assembly needs to be present at compile time and it'll be referenced from the metadata, but it won't be loaded until the first time that one of its functions is close to being executed (it's better explained here).

Linux can load Shared Objects (SO's) also in a purely static manner (statically linked) or in a purely dynamic fashion (using dlopen rather than LoadLibrary and dlsym rather than GetProcAddress)

And now the question is, how do we delay-load Shared Objects in the Linux world?
Well, to my surprise, based on this question/answer it can't be done!

You can read more about the loading of Shared Libraries here