Move to multi arch support and added memory map

src/main.zig

@@ -1,5 +1,6 @@
 const std = @import("std");
 const danos = @import("danos");
+const arch = @import("arch");
 const console = @import("console.zig");
 const BootInfo = danos.BootInfo;
 
@@ -33,15 +34,20 @@ fn kmain(boot_info: *const BootInfo) noreturn {
     con.print("  pitch      : {d} bytes\n", .{fb.pitch});
     con.print("  format     : {s}\n", .{@tagName(fb.format)});
     con.print("  framebuffer: 0x{x:0>16}\n", .{fb.base});
+
+    // Summarise the physical memory the loader handed us. The array is danos's
+    // own MemoryRegion, so this is a plain slice — no firmware layout in sight.
+    const regions = @as([*]const danos.MemoryRegion, @ptrFromInt(boot_info.memory_map.regions))[0..boot_info.memory_map.len];
+    var usable_pages: u64 = 0;
+    for (regions) |r| {
+        if (r.kind == .usable) usable_pages += r.pages;
+    }
+    con.print("  mem regions: {d}\n", .{regions.len});
+    con.print("  usable RAM : {d} MiB\n", .{usable_pages * danos.page_size / (1024 * 1024)});
+
     con.write("\nkernel initialised; nothing left to do, halting.\n");
 
-    hang();
-}
-
-/// Stop the CPU. `hlt` in a loop parks the core at near-zero power until the
-/// next interrupt; we loop because `hlt` returns when one arrives.
-fn hang() noreturn {
-    while (true) asm volatile ("hlt");
+    arch.halt();
 }
 
 /// Freestanding has no OS to receive a panic. Print it to the console (if it is
@@ -55,6 +61,6 @@ pub const panic = std.debug.FullPanic(struct {
             con.write(msg);
             con.write("\n");
         }
-        hang();
+        arch.halt();
     }
 }.panic);