From ee21d1338198a9eb2b15e0b48409752e69bd7901 Mon Sep 17 00:00:00 2001
From: Dean Michael Berris <dberris@google.com>
Date: Thu, 2 Feb 2017 07:51:21 +0000
Subject: [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
---
 lib/xray/xray_AArch64.cc      |  3 +++
 lib/xray/xray_arm.cc          |  3 +++
 lib/xray/xray_emulate_tsc.h   |  5 ++++-
 lib/xray/xray_inmemory_log.cc |  5 +++++
 lib/xray/xray_x86_64.cc       | 22 ++++++++++++++++++++--
 lib/xray/xray_x86_64.h        |  3 +++
 6 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/lib/xray/xray_AArch64.cc b/lib/xray/xray_AArch64.cc
index af06bdbf2..952a4c7eb 100644
--- a/lib/xray/xray_AArch64.cc
+++ b/lib/xray/xray_AArch64.cc
@@ -120,4 +120,7 @@ bool patchFunctionTailExit(const bool Enable, const uint32_t FuncId,
   return patchSled(Enable, FuncId, Sled, __xray_FunctionTailExit);
 }
 
+// FIXME: Maybe implement this better?
+bool probeRequiredCPUFeatures() XRAY_NEVER_INSTRUMENT { return true; }
+
 } // namespace __xray
diff --git a/lib/xray/xray_arm.cc b/lib/xray/xray_arm.cc
index bf36ea067..73e9b4111 100644
--- a/lib/xray/xray_arm.cc
+++ b/lib/xray/xray_arm.cc
@@ -156,4 +156,7 @@ bool patchFunctionTailExit(const bool Enable, const uint32_t FuncId,
   return patchSled(Enable, FuncId, Sled, __xray_FunctionTailExit);
 }
 
+// FIXME: Maybe implement this better?
+bool probeRequiredCPUFeatures() XRAY_NEVER_INSTRUMENT { return true; }
+
 } // namespace __xray
diff --git a/lib/xray/xray_emulate_tsc.h b/lib/xray/xray_emulate_tsc.h
index a3e8b1c92..5285931dd 100644
--- a/lib/xray/xray_emulate_tsc.h
+++ b/lib/xray/xray_emulate_tsc.h
@@ -35,6 +35,9 @@ ALWAYS_INLINE uint64_t readTSC(uint8_t &CPU) XRAY_NEVER_INSTRUMENT {
   CPU = 0;
   return TS.tv_sec * NanosecondsPerSecond + TS.tv_nsec;
 }
-}
+
+bool probeRequiredCPUFeatures();
+
+} // namespace __xray
 
 #endif // XRAY_EMULATE_TSC_H
diff --git a/lib/xray/xray_inmemory_log.cc b/lib/xray/xray_inmemory_log.cc
index d25a61bdb..9decfc437 100644
--- a/lib/xray/xray_inmemory_log.cc
+++ b/lib/xray/xray_inmemory_log.cc
@@ -138,6 +138,11 @@ void __xray_InMemoryRawLog(int32_t FuncId,
 }
 
 static auto Unused = [] {
+  if (!probeRequiredCPUFeatures()) {
+    Report("Required CPU features missing for XRay instrumentation, not "
+           "installing instrumentation hooks.\n");
+    return false;
+  }
   if (flags()->xray_naive_log)
     __xray_set_handler(__xray_InMemoryRawLog);
   return true;
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
diff --git a/lib/xray/xray_x86_64.h b/lib/xray/xray_x86_64.h
index e3de99d63..6b2bbebb7 100644
--- a/lib/xray/xray_x86_64.h
+++ b/lib/xray/xray_x86_64.h
@@ -27,6 +27,9 @@ ALWAYS_INLINE uint64_t readTSC(uint8_t &CPU) XRAY_NEVER_INSTRUMENT {
   CPU = LongCPU;
   return TSC;
 }
+
+bool probeRequiredCPUFeatures();
+
 } // namespace __xray
 
 #endif // XRAY_X86_64_H
-- 
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