Add validation for WAL segment size in pg_control.

This serves as an additional sanity check to be sure the pg_control format is as expected. The field is useful for being near the end and containing a limited number of discrete values.

src/postgres/interface.c

@@ -180,6 +180,14 @@ pgWalSegmentSizeCheck(unsigned int pgVersion, unsigned int walSegmentSize)
             PG_WAL_SEGMENT_SIZE_DEFAULT);
     }
 
+    // Check that the WAL segment size is valid
+    if (!IsValidWalSegSize(walSegmentSize))
+    {
+        THROW_FMT(
+            FormatError, "wal segment size is %u but must be a power of two between %d and %d inclusive", walSegmentSize,
+            WalSegMinSize, WalSegMaxSize);
+    }
+
     FUNCTION_TEST_RETURN_VOID();
 }
 

src/postgres/interface/static.vendor.h

@@ -244,4 +244,22 @@ Types from src/include/access/transam.h
  */
 #define FirstNormalObjectId		16384
 
+/***********************************************************************************************************************************
+Types from src/include/access/xlog_internal.h
+***********************************************************************************************************************************/
+
+// WalSegMinSize/WalSegMinSize macros
+// ---------------------------------------------------------------------------------------------------------------------------------
+/* wal_segment_size can range from 1MB to 1GB */
+#define WalSegMinSize 1024 * 1024
+#define WalSegMaxSize 1024 * 1024 * 1024
+
+// IsPowerOf2/IsValidWalSegSize macros
+// ---------------------------------------------------------------------------------------------------------------------------------
+/* check that the given size is a valid wal_segment_size */
+#define IsPowerOf2(x) (x > 0 && ((x) & ((x)-1)) == 0)
+#define IsValidWalSegSize(size) \
+	 (IsPowerOf2(size) && \
+	 ((size) >= WalSegMinSize && (size) <= WalSegMaxSize))
+
 #endif