[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

llvm-svn: 293015

2 files changed, 57 insertions, 0 deletions

diff --git a/compiler-rt/include/xray/xray_log_interface.h b/compiler-rt/include/xray/xray_log_interface.h
new file mode 100644
index 00000000000..f98b331101a
--- /dev/null
+++ b/compiler-rt/include/xray/xray_log_interface.h
@@ -0,0 +1,51 @@
+//===-- xray_log_interface.h ----------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of XRay, a function call tracing system.
+//
+// APIs for installing a new logging implementation.
+//===----------------------------------------------------------------------===//
+#ifndef XRAY_XRAY_LOG_INTERFACE_H
+#define XRAY_XRAY_LOG_INTERFACE_H
+
+#include "xray/xray_interface.h"
+#include <stddef.h>
+
+extern "C" {
+
+enum XRayLogInitStatus {
+  XRAY_LOG_UNINITIALIZED = 0,
+  XRAY_LOG_INITIALIZING = 1,
+  XRAY_LOG_INITIALIZED = 2,
+  XRAY_LOG_FINALIZING = 3,
+  XRAY_LOG_FINALIZED = 4,
+};
+
+enum XRayLogFlushStatus {
+  XRAY_LOG_NOT_FLUSHING = 0,
+  XRAY_LOG_FLUSHING = 1,
+  XRAY_LOG_FLUSHED = 2,
+};
+
+struct XRayLogImpl {
+  XRayLogInitStatus (*log_init)(size_t, size_t, void *, size_t);
+  XRayLogInitStatus (*log_finalize)();
+  void (*handle_arg0)(int32_t, XRayEntryType);
+  XRayLogFlushStatus (*flush_log)();
+};
+
+void __xray_set_log_impl(XRayLogImpl Impl);
+XRayLogInitStatus __xray_log_init(size_t BufferSize, size_t MaxBuffers,
+                                  void *Args, size_t ArgsSize);
+XRayLogInitStatus __xray_log_finalize();
+XRayLogFlushStatus __xray_log_flushLog();
+
+} // extern "C"
+
+#endif // XRAY_XRAY_LOG_INTERFACE_H
diff --git a/compiler-rt/include/xray/xray_records.h b/compiler-rt/include/xray/xray_records.h
index 34c236b39bd..71637d1fe95 100644
--- a/compiler-rt/include/xray/xray_records.h
+++ b/compiler-rt/include/xray/xray_records.h
@@ -21,6 +21,7 @@ namespace __xray {
 
 enum FileTypes {
   NAIVE_LOG = 0,
+  FDR_LOG = 1,
 };
 
 // This data structure is used to describe the contents of the file. We use this
@@ -40,6 +41,11 @@ struct alignas(32) XRayFileHeader {
 
   // The frequency by which TSC increases per-second.
   alignas(8) uint64_t CycleFrequency = 0;
+
+  // The current civiltime timestamp, as retrived from 'clock_gettime'. This
+  // allows readers of the file to determine when the file was created or
+  // written down.
+  struct timespec TS;
 } __attribute__((packed));
 
 static_assert(sizeof(XRayFileHeader) == 32, "XRayFileHeader != 32 bytes");