schedule tasks across all cores

Per-core GDT/TSS and AP scheduler entry; fix AP SSE + single_threaded.

src/kernel/main.zig

@@ -267,6 +267,7 @@ fn bringUpSecondaries() void {
     }
     arch.setPageExecutable(ap_trampoline_page);
     arch.prepareSecondaries(ap_trampoline_page);
+    arch.setSecondaryEntry(scheduler.secondaryMain); // where a woken core joins the run loop
 
     log.print("\ndanos: bringing up {d} application processor(s)\n", .{cores.len - 1});
     for (cores[1..], 1..) |core, index| {
@@ -276,7 +277,7 @@ fn bringUpSecondaries() void {
         };
         const stack_top = (@intFromPtr(stack.ptr) + stack.len) & ~@as(usize, 15);
         const pc = scheduler.prepareSecondary(index, core.apic_id);
-        if (arch.startSecondary(core.apic_id, stack_top, @intFromPtr(pc))) {
+        if (arch.startSecondary(core.apic_id, stack_top, @intFromPtr(pc), index)) {
             pc.online = true;
             log.print("  cpu apic_id {d}: online\n", .{core.apic_id});
         } else {