[XRay][compiler-rt] XRay Flight Data Recorder Mode

Summary:
In this change we introduce the notion of a "flight data recorder" mode
for XRay logging, where XRay logs in-memory first, and write out data
on-demand as required (as opposed to the naive implementation that keeps
logging while tracing is "on"). This depends on D26232 where we
implement the core data structure for holding the buffers that threads
will be using to write out records of operation.

This implementation only currently works on x86_64 and depends heavily
on the TSC math to write out smaller records to the inmemory buffers.

Also, this implementation defines two different kinds of records with
different sizes (compared to the current naive implementation): a
MetadataRecord (16 bytes) and a FunctionRecord (8 bytes). MetadataRecord
entries are meant to write out information like the thread ID for which
the metadata record is defined for, whether the execution of a thread
moved to a different CPU, etc. while a FunctionRecord represents the
different kinds of function call entry/exit records we might encounter
in the course of a thread's execution along with a delta from the last
time the logging handler was called.

While this implementation is not exactly what is described in the
original XRay whitepaper, this one gives us an initial implementation
that we can iterate and build upon.

Reviewers: echristo, rSerge, majnemer

Subscribers: mehdi_amini, llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D27038

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@290852 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 23 insertions, 66 deletions

diff --git a/lib/xray/xray_inmemory_log.cc b/lib/xray/xray_inmemory_log.cc
index 7ec56f486..0ddd40f7e 100644
--- a/lib/xray/xray_inmemory_log.cc
+++ b/lib/xray/xray_inmemory_log.cc
@@ -16,8 +16,6 @@
 //===----------------------------------------------------------------------===//
 
 #include <cassert>
-#include <cstdint>
-#include <cstdio>
 #include <fcntl.h>
 #include <mutex>
 #include <sys/stat.h>
@@ -39,6 +37,7 @@
 #include "xray_defs.h"
 #include "xray_flags.h"
 #include "xray_interface_internal.h"
+#include "xray_utils.h"
 
 // __xray_InMemoryRawLog will use a thread-local aligned buffer capped to a
 // certain size (32kb by default) and use it as if it were a circular buffer for
@@ -53,25 +52,6 @@ namespace __xray {
 
 std::mutex LogMutex;
 
-static void retryingWriteAll(int Fd, char *Begin,
-                             char *End) XRAY_NEVER_INSTRUMENT {
-  if (Begin == End)
-    return;
-  auto TotalBytes = std::distance(Begin, End);
-  while (auto Written = write(Fd, Begin, TotalBytes)) {
-    if (Written < 0) {
-      if (errno == EINTR)
-        continue; // Try again.
-      Report("Failed to write; errno = %d\n", errno);
-      return;
-    }
-    TotalBytes -= Written;
-    if (TotalBytes == 0)
-      break;
-    Begin += Written;
-  }
-}
-
 class ThreadExitFlusher {
   int Fd;
   XRayRecord *Start;
@@ -102,50 +82,6 @@ public:
 
 using namespace __xray;
 
-void PrintToStdErr(const char *Buffer) XRAY_NEVER_INSTRUMENT {
-  fprintf(stderr, "%s", Buffer);
-}
-
-static int __xray_OpenLogFile() XRAY_NEVER_INSTRUMENT {
-  // FIXME: Figure out how to make this less stderr-dependent.
-  SetPrintfAndReportCallback(PrintToStdErr);
-  // Open a temporary file once for the log.
-  static char TmpFilename[256] = {};
-  static char TmpWildcardPattern[] = "XXXXXX";
-  auto E = internal_strncat(TmpFilename, flags()->xray_logfile_base,
-                            sizeof(TmpFilename) - 10);
-  if (static_cast<size_t>((E + 6) - TmpFilename) > (sizeof(TmpFilename) - 1)) {
-    Report("XRay log file base too long: %s\n", flags()->xray_logfile_base);
-    return -1;
-  }
-  internal_strncat(TmpFilename, TmpWildcardPattern,
-                   sizeof(TmpWildcardPattern) - 1);
-  int Fd = mkstemp(TmpFilename);
-  if (Fd == -1) {
-    Report("XRay: Failed opening temporary file '%s'; not logging events.\n",
-           TmpFilename);
-    return -1;
-  }
-  if (Verbosity())
-    fprintf(stderr, "XRay: Log file in '%s'\n", TmpFilename);
-
-  // Since we're here, we get to write the header. We set it up so that the
-  // header will only be written once, at the start, and let the threads
-  // logging do writes which just append.
-  XRayFileHeader Header;
-  Header.Version = 1;
-  Header.Type = FileTypes::NAIVE_LOG;
-  Header.CycleFrequency = __xray::cycleFrequency();
-
-  // FIXME: Actually check whether we have 'constant_tsc' and 'nonstop_tsc'
-  // before setting the values in the header.
-  Header.ConstantTSC = 1;
-  Header.NonstopTSC = 1;
-  retryingWriteAll(Fd, reinterpret_cast<char *>(&Header),
-                   reinterpret_cast<char *>(&Header) + sizeof(Header));
-  return Fd;
-}
-
 void __xray_InMemoryRawLog(int32_t FuncId,
                            XRayEntryType Type) XRAY_NEVER_INSTRUMENT {
   using Buffer =
@@ -153,7 +89,28 @@ void __xray_InMemoryRawLog(int32_t FuncId,
   static constexpr size_t BuffLen = 1024;
   thread_local static Buffer InMemoryBuffer[BuffLen] = {};
   thread_local static size_t Offset = 0;
-  static int Fd = __xray_OpenLogFile();
+  static int Fd = []() {
+    int F = getLogFD();
+    auto CPUFrequency = getCPUFrequency();
+    if (F == -1)
+      return -1;
+    // Since we're here, we get to write the header. We set it up so that the
+    // header will only be written once, at the start, and let the threads
+    // logging do writes which just append.
+    XRayFileHeader Header;
+    Header.Version = 1;
+    Header.Type = FileTypes::NAIVE_LOG;
+    Header.CycleFrequency =
+        CPUFrequency == -1 ? 0 : static_cast<uint64_t>(CPUFrequency);
+
+    // FIXME: Actually check whether we have 'constant_tsc' and 'nonstop_tsc'
+    // before setting the values in the header.
+    Header.ConstantTSC = 1;
+    Header.NonstopTSC = 1;
+    retryingWriteAll(Fd, reinterpret_cast<char *>(&Header),
+                     reinterpret_cast<char *>(&Header) + sizeof(Header));
+    return F;
+  }();
   if (Fd == -1)
     return;
   thread_local __xray::ThreadExitFlusher Flusher(