Parse ACPI Tables for Hardware Discovery

ACPI table discovery

ACPI describes hardware configuration in memory-resident tables rooted at the RSDP (Root System Description Pointer). The BIOS or UEFI publishes the RSDP; the OS or bootloader scans for the signature "RSD PTR " in ROM or UEFI config tables. For example, from the RSDP you follow pointers to the RSDT or XSDT, then each entry names tables like FADT, MADT, and MCFG.

Parsing flow

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• RSDP: Located via EFI ACPI_20_TABLE_GUID or legacy search (0xE0000-0xFFFFF)
• FADT: Fixed ACPI Description Table (PM timer, SCI interrupt, SMI cmd port)
• MADT: CPU and interrupt controller entries (APIC/IOAPIC)
• Checksums: Each table must sum to zero over its length byte

Tables use 4-byte ASCII signatures and little-endian lengths. Version fields tell you whether 32-bit or 64-bit addresses are valid.

Validation steps

Sum every byte in the table length; ACPI requires an 8-bit checksum of zero. Compare OEM IDs in the FADT with your QEMU machine type to confirm you found the right root. UEFI exposes the RSDP through ConfigurationTable with GUID EB9D2D30-2D88-11D3-9A16-0090273FC14D for ACPI 1.0 and a different GUID for ACPI 2.0+.

Why for this exercise

You will locate the RSDP and walk at least one ACPI header to read a table signature and length. This exercise requires understanding how firmware hands off hardware metadata without legacy BIOS callbacks.