From 56583b1402a7f8fad0f8c3c296e26f12b1114c95 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Thu, 3 Oct 2019 15:02:19 -0400
Subject: updated alarmtest

---
 user/alarmtest.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

(limited to 'user')

diff --git a/user/alarmtest.c b/user/alarmtest.c
index ca3db23..d3746c4 100644
--- a/user/alarmtest.c
+++ b/user/alarmtest.c
@@ -21,7 +21,7 @@ main(int argc, char *argv[])
 {
   test0();
   test1();
-  exit();
+  exit(0);
 }
 
 volatile static int count;
@@ -44,7 +44,7 @@ test0()
   count = 0;
   sigalarm(2, periodic);
   for(i = 0; i < 1000*500000; i++){
-    if((i % 250000) == 0)
+    if((i % 1000000) == 0)
       write(2, ".", 1);
     if(count > 0)
       break;
@@ -53,7 +53,7 @@ test0()
   if(count > 0){
     printf("test0 passed\n");
   } else {
-    printf("test0 failed\n");
+    printf("\ntest0 failed: the kernel never called the alarm handler\n");
   }
 }
 
@@ -64,6 +64,14 @@ void __attribute__ ((noinline)) foo(int i, int *j) {
   *j += 1;
 }
 
+//
+// tests that the kernel calls the handler multiple times.
+//
+// tests that, when the handler returns, it returns to
+// the point in the program where the timer interrupt
+// occurred, with all registers holding the same values they
+// held when the interrupt occurred.
+//
 void
 test1()
 {
@@ -79,9 +87,19 @@ test1()
       break;
     foo(i, &j);
   }
-  if(i != j || count < 10){
-    // i should equal j
-    printf("test1 failed\n");
+  if(count < 10){
+    printf("\ntest1 failed: too few calls to the handler\n");
+    exit(1);
+  } else if(i != j){
+    // the loop should have called foo() i times, and foo() should
+    // have incremented j once per call, so j should equal i.
+    // once possible source of errors is that the handler may
+    // return somewhere other than where the timer interrupt
+    // occurred; another is that that registers may not be
+    // restored correctly, causing i or j or the address ofj
+    // to get an incorrect value.
+    printf("\ntest1 failed: foo() executed fewer times than it was called\n");
+    exit(1);
   } else {
     printf("test1 passed\n");
   }
-- 
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