adding clock system call

system/kernel/tests.zig

@@ -92,6 +92,8 @@ pub fn run(case: []const u8, boot_information: *const BootInformation) void {
         iommuTest();
     } else if (eql(case, "ioport")) {
         ioPortTest();
+    } else if (eql(case, "clock")) {
+        clockTest();
     } else if (eql(case, "smp")) {
         smpTest();
     } else if (eql(case, "affinity")) {
@@ -1100,6 +1102,30 @@ fn ioPortTest() void {
     result();
 }
 
+/// The monotonic clock (the source `clock()` surfaces to user space). It must be
+/// calibrated, move forward over a spin, and never run backwards — the guarantees a
+/// driver's deadline timeout depends on. The syscall is a thin wrapper over this same
+/// `architecture.nanos()`.
+fn clockTest() void {
+    log("DANOS-TEST-BEGIN: clock\n", .{});
+    const t0 = architecture.nanos();
+    check("monotonic clock is calibrated (nonzero)", t0 != 0);
+
+    var last = t0;
+    var monotonic = true;
+    var advanced = false;
+    var i: u32 = 0;
+    while (i < 1_000_000) : (i += 1) {
+        const t = architecture.nanos();
+        if (t < last) monotonic = false;
+        if (t > t0) advanced = true;
+        last = t;
+    }
+    check("clock advanced over the spin", advanced);
+    check("clock never ran backwards (monotonic)", monotonic);
+    result();
+}
+
 var proc_worker_run: bool = true;
 var proc_worker_ran: bool = false;