How to get to know the memory address at which my code/data is actually loaded at boot initialization stage?

In embedded software development, sometimes when you're writing a PIC (position independent code) boot code, you might need to know at which memory address my bootstrap code/data is loaded by a loader at runtime. This article discusses the solutions to this question with assembly language implementation (x86). 

Multiboot Specification and limitations (Bootloader -> OS)

Typically in a computer system, the boot sequence is like this: firmware -> bootloader -> Operating System.  The problem is that nowadays we have the largest variety of operating systems, boot loaders, and firmwares (UEFI/Legacy), and even some of them are proprietary software that are not public. So, the interaction might be a problem if the interface is not well-defined.