0002-Add-PG_NO_PADDING-PG_REQUIRE_NO_PADDING-and-padding-.patch

From 6eeeb7c3d17756e9916b4c0aeb2c993f9c3c013a Mon Sep 17 00:00:00 2001
From: Zsolt Parragi <zsolt.parragi@percona.com>
Date: Tue, 17 Mar 2026 16:19:39 +0000
Subject: [PATCH 2/4] Add PG_NO_PADDING, PG_REQUIRE_NO_PADDING, and padding
 helper macros

Introduce compiler annotation macros in c.h for enforcing struct padding
constraints at build time via the pg-tidy clang-tidy plugin:

- PG_NO_PADDING: marks a struct as requiring no implicit padding
- PG_REQUIRE_NO_PADDING: marks a function parameter as requiring that
  the argument type be annotated with PG_NO_PADDING
- pg_padding_1/2/4: helper macros to declare explicit padding fields
  using appropriately sized integer types

Annotate the data parameter of XLogRegisterData() with
PG_REQUIRE_NO_PADDING to enforce that all data written to WAL records
contains no uninitialized padding bytes.
---
 src/include/access/xloginsert.h |  2 +-
 src/include/c.h                 | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/include/access/xloginsert.h b/src/include/access/xloginsert.h
index 16ebc76e743..527d40c7531 100644
--- a/src/include/access/xloginsert.h
+++ b/src/include/access/xloginsert.h
@@ -46,7 +46,7 @@ extern void XLogSetRecordFlags(uint8 flags);
 extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info);
 extern XLogRecPtr XLogSimpleInsertInt64(RmgrId rmid, uint8 info, int64 value);
 extern void XLogEnsureRecordSpace(int max_block_id, int ndatas);
-extern void XLogRegisterData(const void *data, uint32 len);
+extern void XLogRegisterData(const void *data PG_REQUIRE_NO_PADDING, uint32 len);
 extern void XLogRegisterBuffer(uint8 block_id, Buffer buffer, uint8 flags);
 extern void XLogRegisterBlock(uint8 block_id, RelFileLocator *rlocator,
 							  ForkNumber forknum, BlockNumber blknum, const PageData *page,
diff --git a/src/include/c.h b/src/include/c.h
index fb0ea1bc680..9601455b7fb 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -274,6 +274,35 @@
  */
 #endif
 
+/*
+ * PG_NO_PADDING marks a struct definition as requiring no implicit padding.
+ * When pg-tidy clang-tidy checks are enabled, structs with this annotation
+ * will be verified at build time to contain no compiler-inserted padding.
+ *
+ * PG_REQUIRE_NO_PADDING marks a function parameter as requiring that the
+ * argument type be annotated with PG_NO_PADDING.
+ *
+ * These use compiler annotations that are checked by the pg-tidy clang-tidy
+ * plugin.  On compilers that don't support annotations, they expand to
+ * nothing.
+ */
+#ifdef __clang__
+#define PG_NO_PADDING __attribute__((annotate("pg_no_padding")))
+#define PG_REQUIRE_NO_PADDING __attribute__((annotate("pg_requires_no_padding")))
+#else
+#define PG_NO_PADDING
+#define PG_REQUIRE_NO_PADDING
+#endif
+
+/*
+ * Macros for explicit struct padding.  Use these to replace implicit
+ * compiler-inserted padding in structs marked PG_NO_PADDING.  Each macro
+ * declares a field of the appropriately sized integer type.
+ */
+#define pg_padding_1(name) uint8 name
+#define pg_padding_2(name) uint16 name
+#define pg_padding_4(name) uint32 name
+
 /*
  * Use "pg_attribute_always_inline" in place of "inline" for functions that
  * we wish to force inlining of, even when the compiler's heuristics would
-- 
2.43.0