[Tarantool-patches] [PATCH v2 09/10] port: make port_c_entry not PACKED

[Vladislav Shpilevoy]

PACKED structures don't have padding between their members and
after the structure (needed to be able to store them in an array).

Port_c_entry was PACKED, since it does not have padding between
its members anyway, and the padding in the end was not needed,
because these objects are never stored in an array. As a result,
sizeof(port_c_entry) was not aligned too.

Appeared, that mempool, used to allocate port_c_entry objects,
can't work correctly, when object size is not aligned at least by
8 bytes. Because mempool does not do any alignment internally, and
uses the free objects as a temporary storage for some metadata,
requiring 8 byte alignment.

The patch removes PACKED attribute from port_c_entry, so now its
size is aligned by 8 bytes, and mempool works fine.

Part of #4609
---
 src/box/lua/schema.lua |  2 +-
 src/box/port.h         | 10 +---------
 src/lib/core/port.h    |  2 +-
 3 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/src/box/lua/schema.lua b/src/box/lua/schema.lua
index cdfbb65f7..e6844b45f 100644
--- a/src/box/lua/schema.lua
+++ b/src/box/lua/schema.lua
@@ -79,7 +79,7 @@ ffi.cdef[[
     box_txn_savepoint_t *
     box_txn_savepoint();
 
-    struct __attribute__((packed)) port_c_entry {
+    struct port_c_entry {
         struct port_c_entry *next;
         union {
             struct tuple *tuple;
diff --git a/src/box/port.h b/src/box/port.h
index 76bb5ed1b..43d0f9deb 100644
--- a/src/box/port.h
+++ b/src/box/port.h
@@ -106,12 +106,7 @@ void
 port_vdbemem_create(struct port *base, struct sql_value *mem,
 		    uint32_t mem_count);
 
-/**
- * The struct is PACKED to avoid unnecessary 4 byte padding
- * after mp_size. These objects are never stored on stack, neither
- * allocated as an array, so the padding is not needed.
- */
-struct PACKED port_c_entry {
+struct port_c_entry {
 	struct port_c_entry *next;
 	union {
 		/** Valid if mp_size is 0. */
@@ -126,9 +121,6 @@ struct PACKED port_c_entry {
 	uint32_t mp_size;
 };
 
-static_assert(sizeof(struct port_c_entry) == 20,
-	      "port_c_entry is expected to be perfectly aligned and packed");
-
 /**
  * C port is used by C functions from the public API. They can
  * return tuples and arbitrary MessagePack.
diff --git a/src/lib/core/port.h b/src/lib/core/port.h
index bb7787679..5c51f76e1 100644
--- a/src/lib/core/port.h
+++ b/src/lib/core/port.h
@@ -122,7 +122,7 @@ struct port {
 	 * Implementation dependent content. Needed to declare
 	 * an abstract port instance on stack.
 	 */
-	char pad[52];
+	char pad[60];
 };
 
 /** Is not inlined just to be exported. */
-- 
2.21.1 (Apple Git-122.3)