[XRay][compiler-rt] Add support for TSC emulation for x86_64 to xray_fdr_logging.cc

[dyung]

Summary

Previously in r297800, a work-around was created to use TSC emulation on x86_64 when RDTSCP was not available on the host. A similar change was needed in the file xray_fdr_logging.cc which this patch ports over to that file.

Eventually the code should be refactored as there will be 3 locations with the same code, but that can be done as a separate step. This patch is just to keep the test from failing on my machine due to an illegal instruction since RDTSCP is not available on my x86_64 linux VM.

[dberris]

LGTM

lib/xray/xray_fdr_logging.cc

199

Probably want to put a //FIXME: here indicating that this needs some refactoring later on.

lib/xray/xray_fdr_logging.cc

 }
 
 void fdrLoggingHandleArg0(int32_t FuncId,
                           XRayEntryType Entry) XRAY_NEVER_INSTRUMENT {
   // We want to get the TSC as early as possible, so that we can check whether
   // we've seen this CPU before. We also do it before we load anything else, to
   // allow for forward progress with the scheduling.
   unsigned char CPU;
-  uint64_t TSC = __xray::readTSC(CPU);
+  uint64_t TSC;
+
+  if(probeRequiredCPUFeatures()) {
+    TSC = __xray::readTSC(CPU);
+  } else {
+    timespec TS;
+    int result = clock_gettime(CLOCK_REALTIME, &TS);
+    if (result != 0) {
+      Report("clock_gettime(2) return %d, errno=%d", result, int(errno));
+      TS = {0, 0};
+    }
+    CPU = 0;
+    TSC = TS.tv_sec * __xray::NanosecondsPerSecond + TS.tv_nsec;
+  }
 
   __xray_fdr_internal::processFunctionHook(FuncId, Entry, TSC, CPU,
                                            clock_gettime, LoggingStatus, BQ);
 }
 
 } // namespace __xray
 
 static auto UNUSED Unused = [] {