RSDT on UEFI-enabled systems

[irusanov]

I have an application, part of which parses all SSDT tables to find a specific one with a given Table OemId signature. If one is found, a specific region signature should be present in this table and that region contains the physical mapped address of the table I need to parse. To find the RSDT/XSDT tables I search for the RSDP in bios area in order to jump to the RSDT/XSDT and then get the addresses for all SSDT tables.

On my Lenovo laptop the pointer is not found in bios area.
I'm stuck at the the part where documentation mentions how to get the RSDP on an UEFI-enabled systems by searching the know GUIDs. I see you have asked about the same 2 years ago. My application is using C#, but I don't really comprehend where to start.
RWEverything shows the XSDT, but not the RSDP.

https://www.reddit.com/r/osdev/comments/qqgxr2/need_help_finding_the_xsdt_table_in_a_system/

5.2.5.2 Finding the RSDP on UEFI Enabled Systems
In Unified Extensible Firmware Interface (UEFI) enabled systems, a pointer to the RSDP structure exists within the
EFI System Table. The OS loader is provided a pointer to the EFI System Table at invocation. The OS loader must
retrieve the pointer to the RSDP structure from the EFI System Table and convey the pointer to OSPM, using an OS
dependent data structure, as part of the hand off of control from the OS loader to the OS.
The OS loader locates the pointer to the RSDP structure by examining the EFI Configuration Table within the EFI
System Table. EFI Configuration Table entries consist of Globally Unique Identifier (GUID)/table pointer pairs. The
UEFI specification defines two GUIDs for ACPI; one for ACPI 1.0 and the other for ACPI 2.0 or later specification
revisions.
The EFI GUID for a pointer to the ACPI 1.0 specification RSDP structure is:
• eb9d2d30-2d88-11d3-9a16-0090273fc14d.
The EFI GUID for a pointer to the ACPI 2.0 or later specification RSDP structure is:
• 8868e871-e4f1-11d3-bc22-0080c73c8881.
5.2. ACPI System Description Tables 140
Advanced Configuration and Power Interface (ACPI) Specification, Version 6.4
The OS loader for an ACPI-compatible OS will search for an RSDP structure pointer (RSDP Structure ) using the
current revision GUID first and if it finds one, will use the corresponding RSDP structure pointer. If the GUID is not
found then the OS loader will search for the RSDP structure pointer using the ACPI 1.0 version GUID.
The OS loader must retrieve the pointer to the RSDP structure from the EFI System Table before assuming platform
control via the EFI ExitBootServices interface. See the UEFI Specification for more information.

PS: Guess I will try to use the Registry method to get the SSDT tables and find the desired one.

[irusanov]

It worked, but the AOD (AMD Overdrive Table) of this Lenovo laptop is almost completely broken, just as I expected. Doesn't follow the standard structure other vendors have, it's beyond my mind why they have modified it to the point where it is unusable. It's not enough that AMD is not consistent at all between different generations/SKUs, but also Lenovo breaking stuff on top of that.