Index: compiler-rt/trunk/lib/xray/xray_inmemory_log.cc
===================================================================
--- compiler-rt/trunk/lib/xray/xray_inmemory_log.cc
+++ compiler-rt/trunk/lib/xray/xray_inmemory_log.cc
@@ -77,7 +77,6 @@
 
 static int __xray_OpenLogFile() XRAY_NEVER_INSTRUMENT {
   int F = getLogFD();
-  auto TSCFrequency = getTSCFrequency();
   if (F == -1)
     return -1;
   // Since we're here, we get to write the header. We set it up so that the
@@ -86,7 +85,9 @@
   XRayFileHeader Header;
   Header.Version = 1;
   Header.Type = FileTypes::NAIVE_LOG;
-  Header.CycleFrequency = TSCFrequency;
+  Header.CycleFrequency = probeRequiredCPUFeatures()
+                              ? getTSCFrequency()
+                              : __xray::NanosecondsPerSecond;
 
   // FIXME: Actually check whether we have 'constant_tsc' and 'nonstop_tsc'
   // before setting the values in the header.
@@ -97,8 +98,9 @@
   return F;
 }
 
-void __xray_InMemoryRawLog(int32_t FuncId,
-                           XRayEntryType Type) XRAY_NEVER_INSTRUMENT {
+template <class RDTSC>
+void __xray_InMemoryRawLog(int32_t FuncId, XRayEntryType Type,
+                           RDTSC ReadTSC) XRAY_NEVER_INSTRUMENT {
   using Buffer =
       std::aligned_storage<sizeof(XRayRecord), alignof(XRayRecord)>::type;
   static constexpr size_t BuffLen = 1024;
@@ -115,7 +117,7 @@
   // through a pointer offset.
   auto &R = reinterpret_cast<__xray::XRayRecord *>(InMemoryBuffer)[Offset];
   R.RecordType = RecordTypes::NORMAL;
-  R.TSC = __xray::readTSC(R.CPU);
+  R.TSC = ReadTSC(R.CPU);
   R.TId = TId;
   R.Type = Type;
   R.FuncId = FuncId;
@@ -129,13 +131,32 @@
   }
 }
 
+void __xray_InMemoryRawLogRealTSC(int32_t FuncId,
+                                  XRayEntryType Type) XRAY_NEVER_INSTRUMENT {
+  __xray_InMemoryRawLog(FuncId, Type, __xray::readTSC);
+}
+
+void __xray_InMemoryEmulateTSC(int32_t FuncId,
+                               XRayEntryType Type) XRAY_NEVER_INSTRUMENT {
+  __xray_InMemoryRawLog(FuncId, Type, [](uint8_t &CPU) XRAY_NEVER_INSTRUMENT {
+    timespec TS;
+    int result = clock_gettime(CLOCK_REALTIME, &TS);
+    if (result != 0) {
+      Report("clock_gettimg(2) return %d, errno=%d.", result, int(errno));
+      TS = {0, 0};
+    }
+    CPU = 0;
+    return TS.tv_sec * __xray::NanosecondsPerSecond + TS.tv_nsec;
+  });
+}
+
 static auto UNUSED Unused = [] {
-  if (!probeRequiredCPUFeatures()) {
-    Report("Required CPU features missing for XRay instrumentation, not "
-           "installing instrumentation hooks.\n");
-    return false;
-  }
+  auto UseRealTSC = probeRequiredCPUFeatures();
+  if (!UseRealTSC)
+    Report("WARNING: Required CPU features missing for XRay instrumentation, "
+           "using emulation instead.\n");
   if (flags()->xray_naive_log)
-    __xray_set_handler(__xray_InMemoryRawLog);
+    __xray_set_handler(UseRealTSC ? __xray_InMemoryRawLogRealTSC
+                                  : __xray_InMemoryEmulateTSC);
   return true;
 }();
Index: compiler-rt/trunk/lib/xray/xray_tsc.h
===================================================================
--- compiler-rt/trunk/lib/xray/xray_tsc.h
+++ compiler-rt/trunk/lib/xray/xray_tsc.h
@@ -13,6 +13,10 @@
 #ifndef XRAY_EMULATE_TSC_H
 #define XRAY_EMULATE_TSC_H
 
+namespace __xray {
+static constexpr uint64_t NanosecondsPerSecond = 1000ULL * 1000 * 1000;
+}
+
 #if defined(__x86_64__)
 #include "xray_x86_64.inc"
 #elif defined(__powerpc64__)
@@ -37,8 +41,6 @@
 
 namespace __xray {
 
-static constexpr uint64_t NanosecondsPerSecond = 1000ULL * 1000 * 1000;
-
 inline bool probeRequiredCPUFeatures() XRAY_NEVER_INSTRUMENT { return true; }
 
 ALWAYS_INLINE uint64_t readTSC(uint8_t &CPU) XRAY_NEVER_INSTRUMENT {
@@ -60,7 +62,7 @@
 } // namespace __xray
 
 #else
-"Unsupported CPU Architecture"
+#error Target architecture is not supported.
 #endif // CPU architecture
 
 #endif // XRAY_EMULATE_TSC_H