How is RSDP passed to kernel?

Hello, The APCI spec says "During OS initialization, OSPM must obtain the Root System Description Pointer (RSDP) structure from the platform. When OSPM locates the Root System Description Pointer (RSDP) structure, it then locates the Root System Description Table (RSDT) or the Extended Root System Description Table (XSDT) using the physical system address supplied in the RSDP." How does the bootloader pass the RSDP to the kernel? What is the most typical method and other options? I remember reading somewhere when it's using UEFI, the value is passed through UEFI system table or like that. I would appreciate if it's just a simple explanation. (though I'm more interested in UEFI case) Thank you. Chan Kim