Index: include/xray/xray_records.h
===================================================================
--- include/xray/xray_records.h
+++ include/xray/xray_records.h
@@ -24,6 +24,14 @@
   FDR_LOG = 1,
 };
 
+// FDR mode use of the union field in the XRayFileHeader.
+struct alignas(16) FdrAdditionalHeaderData {
+  uint64_t ThreadBufferSize;
+};
+
+static_assert(sizeof(FdrAdditionalHeaderData) == 16,
+              "FdrAdditionalHeaderData != 16 bytes");
+
 // This data structure is used to describe the contents of the file. We use this
 // for versioning the supported XRay file formats.
 struct alignas(32) XRayFileHeader {
@@ -42,10 +50,15 @@
   // 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;
+  union {
+    char FreeForm[16];
+    // 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;
+
+    struct FdrAdditionalHeaderData FdrData;
+  };
 } __attribute__((packed));
 
 static_assert(sizeof(XRayFileHeader) == 32, "XRayFileHeader != 32 bytes");
Index: lib/xray/xray_buffer_queue.h
===================================================================
--- lib/xray/xray_buffer_queue.h
+++ lib/xray/xray_buffer_queue.h
@@ -98,6 +98,9 @@
                                     __sanitizer::memory_order_acquire);
   }
 
+  /// Returns the configured size of the buffers in the buffer queue.
+  size_t ConfiguredBufferSize() const { return BufferSize; }
+
   /// Sets the state of the BufferQueue to finalizing, which ensures that:
   ///
   ///   - All subsequent attempts to retrieve a Buffer will fail.
Index: lib/xray/xray_fdr_logging.cc
===================================================================
--- lib/xray/xray_fdr_logging.cc
+++ lib/xray/xray_fdr_logging.cc
@@ -125,12 +125,16 @@
   // before setting the values in the header.
   Header.ConstantTSC = 1;
   Header.NonstopTSC = 1;
-  clock_gettime(CLOCK_REALTIME, &Header.TS);
+  Header.FdrData = FdrAdditionalHeaderData{LocalBQ->ConfiguredBufferSize()};
   retryingWriteAll(Fd, reinterpret_cast<char *>(&Header),
                    reinterpret_cast<char *>(&Header) + sizeof(Header));
+
   LocalBQ->apply([&](const BufferQueue::Buffer &B) {
-    retryingWriteAll(Fd, reinterpret_cast<char *>(B.Buffer),
-                     reinterpret_cast<char *>(B.Buffer) + B.Size);
+    uint64_t BufferSize = B.Size;
+    if (BufferSize > 0) {
+      retryingWriteAll(Fd, reinterpret_cast<char *>(B.Buffer),
+                       reinterpret_cast<char *>(B.Buffer) + B.Size);
+    }
   });
   __sanitizer::atomic_store(&LogFlushStatus,
                             XRayLogFlushStatus::XRAY_LOG_FLUSHED,
Index: lib/xray/xray_fdr_logging_impl.h
===================================================================
--- lib/xray/xray_fdr_logging_impl.h
+++ lib/xray/xray_fdr_logging_impl.h
@@ -311,10 +311,24 @@
     __sanitizer::atomic_sint32_t &LoggingStatus,
     const std::shared_ptr<BufferQueue> &BQ) XRAY_NEVER_INSTRUMENT {
   // Bail out right away if logging is not initialized yet.
-  if (__sanitizer::atomic_load(&LoggingStatus,
-                               __sanitizer::memory_order_acquire) !=
-      XRayLogInitStatus::XRAY_LOG_INITIALIZED)
+  // We should take the opportunity to release the buffer though.
+  auto Status = __sanitizer::atomic_load(&LoggingStatus,
+                                         __sanitizer::memory_order_acquire);
+  if (Status != XRayLogInitStatus::XRAY_LOG_INITIALIZED) {
+    if (RecordPtr != nullptr &&
+        (Status == XRayLogInitStatus::XRAY_LOG_FINALIZING ||
+         Status == XRayLogInitStatus::XRAY_LOG_FINALIZED)) {
+      writeEOBMetadata();
+      auto EC = BQ->releaseBuffer(Buffer);
+      if (EC != BufferQueue::ErrorCode::Ok) {
+        Report("Failed to release buffer at %p; error=%s\n", Buffer.Buffer,
+               BufferQueue::getErrorString(EC));
+        return;
+      }
+      RecordPtr = nullptr;
+    }
     return;
+  }
 
   // We use a thread_local variable to keep track of which CPUs we've already
   // run, and the TSC times for these CPUs. This allows us to stop repeating the