1 files changed, 26 insertions, 5 deletions
diff --git a/lib/libcxx/src/chrono.cpp b/lib/libcxx/src/chrono.cpp
index 085fbfde26..13b375947b 100644
--- a/lib/libcxx/src/chrono.cpp
+++ b/lib/libcxx/src/chrono.cpp
@@ -6,9 +6,20 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if defined(__MVS__)
+// As part of monotonic clock support on z/OS we need macro _LARGE_TIME_API
+// to be defined before any system header to include definition of struct timespec64.
+#define _LARGE_TIME_API
+#endif
+
 #include "chrono"
 #include "cerrno"        // errno
 #include "system_error"  // __throw_system_error
+
+#if defined(__MVS__)
+#include <__support/ibm/gettod_zos.h> // gettimeofdayMonotonic
+#endif
+
 #include <time.h>        // clock_gettime and CLOCK_{MONOTONIC,REALTIME,MONOTONIC_RAW}
 #include "include/apple_availability.h"
 
@@ -20,7 +31,7 @@
 # include <sys/time.h> // for gettimeofday and timeval
 #endif
 
-#if !defined(__APPLE__) && _POSIX_TIMERS > 0
+#if !defined(__APPLE__) && defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0
 # define _LIBCPP_USE_CLOCK_GETTIME
 #endif
 
@@ -96,19 +107,19 @@ static system_clock::time_point __libcpp_system_clock_now() {
 const bool system_clock::is_steady;
 
 system_clock::time_point
-system_clock::now() _NOEXCEPT
+system_clock::now() noexcept
 {
     return __libcpp_system_clock_now();
 }
 
 time_t
-system_clock::to_time_t(const time_point& t) _NOEXCEPT
+system_clock::to_time_t(const time_point& t) noexcept
 {
     return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
 }
 
 system_clock::time_point
-system_clock::from_time_t(time_t t) _NOEXCEPT
+system_clock::from_time_t(time_t t) noexcept
 {
     return system_clock::time_point(seconds(t));
 }
@@ -218,6 +229,16 @@ static steady_clock::time_point __libcpp_steady_clock_now() {
   return steady_clock::time_point(steady_clock::duration(dur));
 }
 
+#elif defined(__MVS__)
+
+static steady_clock::time_point __libcpp_steady_clock_now() {
+  struct timespec64 ts;
+  if (0 != gettimeofdayMonotonic(&ts))
+    __throw_system_error(errno, "failed to obtain time of day");
+
+  return steady_clock::time_point(seconds(ts.tv_sec) + nanoseconds(ts.tv_nsec));
+}
+
 #elif defined(CLOCK_MONOTONIC)
 
 static steady_clock::time_point __libcpp_steady_clock_now() {
@@ -234,7 +255,7 @@ static steady_clock::time_point __libcpp_steady_clock_now() {
 const bool steady_clock::is_steady;
 
 steady_clock::time_point
-steady_clock::now() _NOEXCEPT
+steady_clock::now() noexcept
 {
     return __libcpp_steady_clock_now();
 }