[XRay] Probe for CPU features that XRay needs

Summary:
In llvm.org/PR31756 it's pointed out that sometimes rdtscp isn't
available. We fix it here by checking first whether it's availble before
installing the logging handler. In future commits we can have
alternative implementations, maybe working around some of the
constraints on some systems.

This change enables us to make that determination, but report an error
instead when the features aren't available.

Reviewers: sdardis, javed.absar, rSerge

Subscribers: pelikan, llvm-commits

Differential Revision: https://reviews.llvm.org/D29438

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@293870 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 20 insertions, 2 deletions

diff --git a/lib/xray/xray_x86_64.cc b/lib/xray/xray_x86_64.cc
index 3ee91896c..25c64957c 100644
--- a/lib/xray/xray_x86_64.cc
+++ b/lib/xray/xray_x86_64.cc
@@ -1,6 +1,8 @@
+#include "cpuid.h"
 #include "sanitizer_common/sanitizer_common.h"
 #include "xray_defs.h"
 #include "xray_interface_internal.h"
+
 #include <atomic>
 #include <cstdint>
 #include <errno.h>
@@ -61,8 +63,8 @@ uint64_t cycleFrequency() XRAY_NEVER_INSTRUMENT {
                         &CPUFrequency)) {
     CPUFrequency *= 1000;
   } else if (readValueFromFile(
-      "/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq",
-      &CPUFrequency)) {
+                 "/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq",
+                 &CPUFrequency)) {
     CPUFrequency *= 1000;
   } else {
     Report("Unable to determine CPU frequency for TSC accounting.\n");
@@ -199,4 +201,20 @@ bool patchFunctionTailExit(const bool Enable, const uint32_t FuncId,
   return true;
 }
 
+// We determine whether the CPU we're running on has the correct features we
+// need. In x86_64 this will be rdtscp support.
+bool probeRequiredCPUFeatures() XRAY_NEVER_INSTRUMENT {
+  unsigned int EAX, EBX, ECX, EDX;
+
+  // We check whether rdtscp support is enabled. According to the x86_64 manual,
+  // level should be set at 0x80000001, and we should have a look at bit 27 in
+  // EDX. That's 0x8000000 (or 1u << 26).
+  __get_cpuid(0x80000001, &EAX, &EBX, &ECX, &EDX);
+  if (!(EDX & (1u << 26))) {
+    Report("Missing rdtscp support.\n");
+    return false;
+  }
+  return true;
+}
+
 } // namespace __xray