Is DLL always have the same Base Address?

Question

I'm studying about windows and DLL stuffs and I have some question about it. :)

I made a simple program that loads my own DLL. This DLL has just simple functions, plus, minus.

This is the question : if I load some DLL (for example, text.dll), is this DLL always have the same Base Address? or it changes when I restart it? and can I hold the DLL's Base Address?

When I test it, it always have same Base Address, but I think when I need to do about this, I have to make some exception about the DLL Base Address.

Answer 1

The operating system will load your DLL in whatever base address it pleases. You can specify a "preferred" base address, but if that does not happen to be available, (for whatever reason, which may well be completely out of your control,) your DLL will be relocated by the operating system to whatever address the operating system sees fit.

Answer 2

i load some DLL(for example, text.dll), is this DLL always have the same Base Address?

No. It is a preferred base address. If something is already loaded at that address, the loader will rebase it and fixup all of the addresses.

Other things, like Address Space Layout Randomization could cause it to be different every time the process starts.