[chrony-dev] [PATCH] macOS 11.0 (Big Sur) beta - Bug in implementation of ntp_adjtime()

[Bryan Christianson <bryan@xxxxxxxxxxxxx>]

macOS 11.0 (Big Sur) beta incorrectly returns timex.freq as an unsigned number. This patch is a workaround for the bug and should be removed when Apple fix the problem (assuming they will). The patch also extends the ntpadjtime test to cover negative frequencies.
---
 sys_timex.c              | 23 +++++++++++++++++++++--
 test/kernel/ntpadjtime.c |  2 +-
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/sys_timex.c b/sys_timex.c
index 0a6b438..aa1508a 100644
--- a/sys_timex.c
+++ b/sys_timex.c
@@ -68,6 +68,25 @@ static int sys_tai_offset;
 
 /* ================================================== */
 
+static inline double
+txc_freq(const struct timex *txc)
+{
+  double freq_ppm;
+
+  freq_ppm = txc->freq / FREQ_SCALE;
+
+#ifdef MACOSX
+  /* temporary work-around for Apple bug treating freq as unsigned number */
+  if (freq_ppm > 32767) {
+    freq_ppm -= 65536;
+  }
+#endif
+
+  return -freq_ppm;
+}
+
+/* ================================================== */
+
 static double
 read_frequency(void)
 {
@@ -77,7 +96,7 @@ read_frequency(void)
 
   SYS_Timex_Adjust(&txc, 0);
 
-  return txc.freq / -FREQ_SCALE;
+  return txc_freq(&txc);
 }
 
 /* ================================================== */
@@ -92,7 +111,7 @@ set_frequency(double freq_ppm)
 
   SYS_Timex_Adjust(&txc, 0);
 
-  return txc.freq / -FREQ_SCALE;
+  return txc_freq(&txc);
 }
 
 /* ================================================== */
diff --git a/test/kernel/ntpadjtime.c b/test/kernel/ntpadjtime.c
index d6be154..96c069f 100644
--- a/test/kernel/ntpadjtime.c
+++ b/test/kernel/ntpadjtime.c
@@ -52,7 +52,7 @@ test_freqrange(void)
 
   printf("freq range:\n");
 
-  for (i = 0; i <= 1000; i += 50) {
+  for (i = -1000; i <= 1000; i += 50) {
     t.modes = MOD_FREQUENCY;
     t.freq = i << 16;
     printf("%4d ppm => ", i);
-- 
2.24.3 (Apple Git-128)


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