util: add support for other NTP eras

NTP timestamps use only 32 bits to count seconds and the current NTP era
ends in 2036. Add support for converting NTP timestamps from other NTP
eras on systems with 64-bit time_t.

The earliest assumed NTP time is set by the configure script (by default
to 50 years before the date of the build) and earlier NTP timestamps
underflow to the following NTP era.

configure

@@ -114,6 +114,8 @@ For better control, use the options below.
   --disable-linuxcaps    Disable Linux capabilities support
   --disable-asyncdns     Disable asynchronous name resolving
   --disable-forcednsretry Don't retry on permanent DNS error
+  --with-ntp-era=SECONDS Specify earliest assumed NTP time in seconds
+                         since 1970-01-01 [50*365 days ago]
   --with-user=USER       Specify default chronyd user [root]
   --with-sendmail=PATH   Path to sendmail binary [/usr/lib/sendmail]
   --enable-debug         Enable debugging support
@@ -194,6 +196,7 @@ try_setsched=0
 try_lockmem=0
 feat_asyncdns=1
 feat_forcednsretry=1
+ntp_era_split=""
 default_user="root"
 mail_program="/usr/lib/sendmail"
 
@@ -275,6 +278,9 @@ do
     --disable-forcednsretry)
       feat_forcednsretry=0
     ;;
+    --with-ntp-era=* )
+      ntp_era_split=`echo $option | sed -e 's/^.*=//;'`
+    ;;
     --with-user=* )
       default_user=`echo $option | sed -e 's/^.*=//;'`
     ;;
@@ -381,6 +387,33 @@ if test_code '64-bit time_t' 'time.h' '' '' '
   return x[0];'
 then
   add_def HAVE_LONG_TIME_T 1
+
+  if [ "x$ntp_era_split" != "x" ]; then
+    split_seconds=$ntp_era_split
+    split_days=0
+  else
+    split_seconds=`date '+%s'`
+    if [ "x$split_seconds" = "" ]; then
+      echo "Could not get current time, --with-ntp-era option is needed"
+      exit 1
+    fi
+    split_days=$((50 * 365))
+  fi
+
+  add_def NTP_ERA_SPLIT "(${split_seconds}LL - $split_days * 24 * 3600)"
+
+  date_format='+%Y-%m-%dT%H:%M:%SZ'
+
+  # Print the full NTP interval if a suitable date is found
+  if [ "x`date -u -d '1970-01-01 UTC 9 days ago 5 seconds 3 seconds' \
+    $date_format 2> /dev/null`" = "x1969-12-23T00:00:08Z" ]
+  then
+    time1="`date -u -d "1970-01-01 UTC $split_days days ago $split_seconds seconds" \
+      $date_format`"
+    time2="`date -u -d "1970-01-01 UTC $split_days days ago $split_seconds seconds 4294967296 seconds" \
+      $date_format`"
+    echo "NTP time mapped to $time1/$time2"
+  fi
 fi
 
 MATHCODE='return (int) pow(2.0, log(sqrt((double)argc)));'

ntp_core.c

@@ -258,10 +258,35 @@ do_size_checks(void)
 
 /* ================================================== */
 
+static void
+do_time_checks(void)
+{
+#ifdef HAVE_LONG_TIME_T
+  /* Check that time before NTP_ERA_SPLIT underflows correctly */
+
+  struct timeval tv1 = {NTP_ERA_SPLIT, 1}, tv2 = {NTP_ERA_SPLIT - 1, 1};
+  NTP_int64 ntv1, ntv2;
+  int r;
+
+  UTI_TimevalToInt64(&tv1, &ntv1, 0);
+  UTI_TimevalToInt64(&tv2, &ntv2, 0);
+  UTI_Int64ToTimeval(&ntv1, &tv1);
+  UTI_Int64ToTimeval(&ntv2, &tv2);
+
+  r = tv1.tv_sec == NTP_ERA_SPLIT &&
+      tv1.tv_sec + (1ULL << 32) - 1 == tv2.tv_sec;
+
+  assert(r);
+#endif
+}
+
+/* ================================================== */
+
 void
 NCR_Initialise(void)
 {
   do_size_checks();
+  do_time_checks();
 
   logfileid = CNF_GetLogMeasurements() ? LOG_FileOpen("measurements",
       "   Date (UTC) Time     IP Address   L St 1234 abc 5678 LP RP Score Offset     Peer del. Peer disp. Root del.  Root disp.")

util.c

@@ -498,16 +498,17 @@ void
 UTI_TimevalToInt64(struct timeval *src,
                    NTP_int64 *dest, uint32_t fuzz)
 {
-  unsigned long usec = src->tv_usec;
-  unsigned long sec = src->tv_sec;
-  uint32_t lo;
+  uint32_t lo, sec, usec;
+
+  sec = (uint32_t)src->tv_sec;
+  usec = (uint32_t)src->tv_usec;
 
   /* Recognize zero as a special case - it always signifies
      an 'unknown' value */
   if (!usec && !sec) {
     dest->hi = dest->lo = 0;
   } else {
-    dest->hi = htonl(src->tv_sec + JAN_1970);
+    dest->hi = htonl(sec + JAN_1970);
 
     /* This formula gives an error of about 0.1us worst case */
     lo = 4295 * usec - (usec>>5) - (usec>>9);
@@ -525,13 +526,23 @@ void
 UTI_Int64ToTimeval(NTP_int64 *src,
                    struct timeval *dest)
 {
+  uint32_t ntp_sec, ntp_frac;
+
   /* As yet, there is no need to check for zero - all processing that
      has to detect that case is in the NTP layer */
 
-  dest->tv_sec = ntohl(src->hi) - JAN_1970;
+  ntp_sec = ntohl(src->hi);
+  ntp_frac = ntohl(src->lo);
+
+#ifdef HAVE_LONG_TIME_T
+  dest->tv_sec = ntp_sec - (uint32_t)(NTP_ERA_SPLIT + JAN_1970) +
+                 (time_t)NTP_ERA_SPLIT;
+#else
+  dest->tv_sec = ntp_sec - JAN_1970;
+#endif
   
   /* Until I invent a slick way to do this, just do it the obvious way */
-  dest->tv_usec = (int)(0.5 + (double)(ntohl(src->lo)) / 4294.967296);
+  dest->tv_usec = (int)(0.5 + (double)(ntp_frac) / 4294.967296);
 }
 
 /* ================================================== */