add alarmtest.c to the repository

they don't have to modify alarmtest.c, so we can use the
original version to test, to make it harder to cheat.

user/alarmtest.c

@@ -0,0 +1,88 @@
+//
+// test program for the alarm lab.
+// you can modify this file for testing,
+// but please make sure your kernel
+// modifications pass the original
+// versions of these tests.
+//
+
+#include "kernel/param.h"
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "kernel/riscv.h"
+#include "user/user.h"
+
+void test0();
+void test1();
+void periodic();
+
+int
+main(int argc, char *argv[])
+{
+  test0();
+  test1();
+  exit();
+}
+
+volatile static int count;
+
+void
+periodic()
+{
+  count = count + 1;
+  printf(1, "alarm!\n");
+  sigreturn();
+}
+
+// tests whether the kernel calls
+// the alarm handler even a single time.
+void
+test0()
+{
+  int i;
+  printf(1, "test0 start\n");
+  count = 0;
+  sigalarm(2, periodic);
+  for(i = 0; i < 1000*500000; i++){
+    if((i % 250000) == 0)
+      write(2, ".", 1);
+    if(count > 0)
+      break;
+  }
+  sigalarm(0, 0);
+  if(count > 0){
+    printf(1, "test0 passed\n");
+  } else {
+    printf(1, "test0 failed\n");
+  }
+}
+
+void __attribute__ ((noinline)) foo(int i, int *j) {
+  if((i % 2500000) == 0) {
+    write(2, ".", 1);
+  }
+  *j += 1;
+}
+
+void
+test1()
+{
+  int i;
+  int j;
+
+  printf(1, "test1 start\n");
+  count = 0;
+  j = 0;
+  sigalarm(2, periodic);
+  for(i = 0; i < 500000000; i++){
+    if(count >= 10)
+      break;
+    foo(i, &j);
+  }
+  if(i != j || count < 10){
+    // i should equal j
+    printf(1, "test1 failed\n");
+  } else {
+    printf(1, "test1 passed\n");
+  }
+}