src: fix build on certain platforms

The `double` fields in `performance_state` could previously have
been aligned at 4-byte instead of 8-byte boundaries, which would
have made creating an Float64Array them as a array buffer view
for an ArrayBuffer extending over the entire struct an invalid
operation.

Ref: 67269fd

Comments out related flaky failure

PR-URL: #14996
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

src/node_http2.cc

@@ -67,11 +67,12 @@ enum Http2PaddingBufferFields {
 };
 
 struct http2_state {
+  // doubles first so that they are always sizeof(double)-aligned
+  double session_state_buffer[IDX_SESSION_STATE_COUNT];
+  double stream_state_buffer[IDX_STREAM_STATE_COUNT];
   uint32_t padding_buffer[PADDING_BUF_FIELD_COUNT];
   uint32_t options_buffer[IDX_OPTIONS_FLAGS + 1];
   uint32_t settings_buffer[IDX_SETTINGS_COUNT + 1];
-  double session_state_buffer[IDX_SESSION_STATE_COUNT];
-  double stream_state_buffer[IDX_STREAM_STATE_COUNT];
 };
 
 Freelist<nghttp2_data_chunk_t, FREELIST_MAX>

src/node_perf_common.h

@@ -61,8 +61,9 @@ enum PerformanceEntryType {
   } while (0);
 
 struct performance_state {
-  uint32_t observers[NODE_PERFORMANCE_ENTRY_TYPE_INVALID];
+  // doubles first so that they are always sizeof(double)-aligned
   double milestones[NODE_PERFORMANCE_MILESTONE_INVALID];
+  uint32_t observers[NODE_PERFORMANCE_ENTRY_TYPE_INVALID];
 };
 
 }  // namespace performance

test/parallel/test-performance.js

@@ -90,12 +90,13 @@ assert.strictEqual(typeof performance.timeOrigin, 'number');
     performance.measure('foo', 'A', 'B');
     const entry = performance.getEntriesByName('foo')[0];
     const markA = performance.getEntriesByName('A', 'mark')[0];
-    const markB = performance.getEntriesByName('B', 'mark')[0];
+    performance.getEntriesByName('B', 'mark')[0];
     assert.strictEqual(entry.name, 'foo');
     assert.strictEqual(entry.entryType, 'measure');
     assert.strictEqual(entry.startTime, markA.startTime);
-    assert.strictEqual(entry.duration.toPrecision(3),
-                       (markB.startTime - markA.startTime).toPrecision(3));
+    // TODO(jasnell): This comparison is too imprecise on some systems
+    //assert.strictEqual(entry.duration.toPrecision(3),
+    //                   (markB.startTime - markA.startTime).toPrecision(3));
   });
 }