1 files changed, 95 insertions, 0 deletions
diff --git a/lib/xray/xray_fdr_logging.h b/lib/xray/xray_fdr_logging.h
new file mode 100644
index 000000000..86c72c259
--- /dev/null
+++ b/lib/xray/xray_fdr_logging.h
@@ -0,0 +1,95 @@
+//===-- xray_fdr_logging.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.
+//
+//===----------------------------------------------------------------------===//
+#ifndef XRAY_XRAY_FDR_LOGGING_H
+#define XRAY_XRAY_FDR_LOGGING_H
+
+#include "xray/xray_log_interface.h"
+
+// FDR (Flight Data Recorder) Mode
+// ===============================
+//
+// The XRay whitepaper describes a mode of operation for function call trace
+// logging that involves writing small records into an in-memory circular
+// buffer, that then gets logged to disk on demand. To do this efficiently and
+// capture as much data as we can, we use smaller records compared to the
+// default mode of always writing fixed-size records.
+
+namespace __xray {
+
+enum class RecordType : uint8_t {
+  Function, Metadata
+};
+
+// A MetadataRecord encodes the kind of record in its first byte, and have 15
+// additional bytes in the end to hold free-form data.
+struct alignas(16) MetadataRecord {
+  // A MetadataRecord must always have a type of 1.
+  RecordType Type : 1;
+
+  // Each kind of record is represented as a 7-bit value (even though we use an
+  // unsigned 8-bit enum class to do so).
+  enum class RecordKinds : uint8_t {
+    NewBuffer,
+    EndOfBuffer,
+    NewCPUId,
+    TSCWrap,
+    WalltimeMarker,
+  };
+  RecordKinds RecordKind : 7; // Use 7 bits to identify this record type.
+  char Data[15];
+} __attribute__((packed));
+
+static_assert(sizeof(MetadataRecord) == 16, "Wrong size for MetadataRecord.");
+
+struct alignas(8) FunctionRecord {
+  // A FunctionRecord must always have a type of 0.
+  RecordType Type : 1;
+  enum class RecordKinds {
+    FunctionEnter = 0x00,
+    FunctionExit = 0x01,
+    FunctionTailExit = 0x02,
+  };
+  RecordKinds RecordKind : 3;
+
+  // We only use 28 bits of the function ID, so that we can use as few bytes as
+  // possible. This means we only support 2^28 (268,435,456) unique function ids
+  // in a single binary.
+  int FuncId : 28;
+
+  // We use another 4 bytes to hold the delta between the previous entry's TSC.
+  // In case we've found that the distance is greater than the allowable 32 bits
+  // (either because we are running in a different CPU and the TSC might be
+  // different then), we should use a MetadataRecord before this FunctionRecord
+  // that will contain the full TSC for that CPU, and keep this to 0.
+  uint32_t TSCDelta;
+} __attribute__((packed));
+
+static_assert(sizeof(FunctionRecord) == 8, "Wrong size for FunctionRecord.");
+
+// Options used by the FDR implementation.
+struct FDRLoggingOptions {
+  bool ReportErrors = false;
+  int Fd = -1;
+};
+
+// Flight Data Recorder mode implementation interfaces.
+XRayLogInitStatus FDRLogging_init(std::size_t BufferSize, std::size_t BufferMax,
+                                  void *Options, size_t OptionsSize);
+XRayLogInitStatus FDRLogging_finalize();
+void FDRLogging_handleArg0(int32_t FuncId, XRayEntryType Entry);
+XRayLogFlushStatus FDRLogging_flush();
+XRayLogInitStatus FDRLogging_reset();
+
+} // namespace __xray
+
+#endif // XRAY_XRAY_FDR_LOGGING_H