add device platform module with ACPI support

src/boot/efi.zig

@@ -38,6 +38,10 @@ fn boot() !noreturn {
         .memory_map = undefined, // filled by exitBootServices, just below
         .kernel_segments = undefined, // filled by loadKernel
         .kernel_segment_count = 0,
+        // Read the ACPI RSDP from the UEFI configuration table now, while boot
+        // services are still up. The pointer lives in ACPI reclaim memory, which
+        // the kernel identity-maps, so the physical address stays valid afterward.
+        .acpi_rsdp = if (acpiRootSystemDescriptorPointer()) |p| @intFromPtr(p) else 0,
     };
 
     const entry = try loadKernel(bs, &boot_info);
@@ -321,7 +325,7 @@ fn convertMemoryMap(map: MemoryMapSlice, out: []u8) danos.MemoryMap {
 /// kernel image and these buffers) lands there and stays reserved.
 fn classify(d: *const uefi.tables.MemoryDescriptor) danos.MemoryKind {
     if (!d.attribute.wb) return .mmio;
-    return switch (d.@"type") {
+    return switch (d.type) {
         .conventional_memory, .boot_services_code, .boot_services_data => .usable,
         .acpi_reclaim_memory => .acpi_tables,
         .acpi_memory_nvs => .acpi_nvs,
@@ -349,3 +353,19 @@ fn logBytes(bytes: []const u8) void {
     buf[i] = 0;
     _ = out.outputString(buf[0..i :0].ptr) catch {};
 }
+
+fn acpiRootSystemDescriptorPointer() ?*const anyopaque {
+    const table_entries = uefi.system_table.number_of_table_entries;
+    const config_tables = uefi.system_table.configuration_table;
+    const acpi2 = uefi.tables.ConfigurationTable.acpi_20_table_guid;
+    const acpi1 = uefi.tables.ConfigurationTable.acpi_10_table_guid;
+
+    for (0..table_entries) |i| {
+        const entry = config_tables[i];
+        if (entry.vendor_guid.eql(acpi2) or entry.vendor_guid.eql(acpi1)) {
+            return entry.vendor_table;
+        }
+    }
+
+    return null;
+}