efi: Expose ACPI RSDP table if present

If there is an ACPI RSDP table in the zero page then expose it through
to the running kernel via the ACPI tables otherwise continue with the
stub data.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

Author: rbradford

src/efi/mod.rs

@@ -786,17 +786,32 @@ pub fn efi_exec(
     };
 
     let vendor_data = 0u32;
-
-    let mut ct = efi::ConfigurationTable {
-        vendor_guid: Guid::from_fields(
-            0x678a_9665,
-            0x9957,
-            0x4e7c,
-            0xa6,
-            0x27,
-            &[0x34, 0xc9, 0x46, 0x3d, 0xd2, 0xac],
-        ),
-        vendor_table: &vendor_data as *const _ as *mut _,
+    let acpi_rsdp_ptr = unsafe { *((ZERO_PAGE_START + 0x70) as u64 as *const u64) };
+
+    let mut ct = if acpi_rsdp_ptr != 0 {
+        efi::ConfigurationTable {
+            vendor_guid: Guid::from_fields(
+                0x8868_e871,
+                0xe4f1,
+                0x11d3,
+                0xbc,
+                0x22,
+                &[0x00, 0x80, 0xc7, 0x3c, 0x88, 0x81],
+            ),
+            vendor_table: acpi_rsdp_ptr as u64 as *mut _,
+        }
+    } else {
+        efi::ConfigurationTable {
+            vendor_guid: Guid::from_fields(
+                0x678a_9665,
+                0x9957,
+                0x4e7c,
+                0xa6,
+                0x27,
+                &[0x34, 0xc9, 0x46, 0x3d, 0xd2, 0xac],
+            ),
+            vendor_table: &vendor_data as *const _ as *mut _,
+        }
     };
 
     let mut st = efi::SystemTable {