Loading/unloading ELF sections on demand?

Question

For a rather obscure use case I'd like to have a (large) statically linked Linux executable made up of a small piece of control code and large pieces of static (read-only) data. Is it possible, to save memory, to get the loader to load only the sections for the control code, and then manually load the sections of RO data as they are needed, and unload them again once the processing is done?

Is this possible?

(I suppose data streams (on the filesystem level) could be used to solve this, but they aren't available to me (EXT3) and distribution would be tricky since data streams easily get lost.)

Answer 1

No, if it's part of the ELF file, it will be mapped. I'm not sure of the particulars of ELF, but if this was a PE file, you could simply tag on your added data to the end of the PE file, beyond the PE structure. Data that isn't part of the PE structure doesn't get mapped to memory in windows. I suspect the same exists in ELF.

Answer 2

This is (very probably) already taken care of for you.

The real answer of course will be system-dependent, but in general, modern operating systems (and certainly Linux) use demand paging for executables, so no RAM will be actually allocated for sections of the ELF file you don't reference.

Answer 3

Instead of linking your blobs into the binary, append them to it. They won't be mapped, but you can read or map them as you need them.