Tighten up size calculation for flexible array members

PiperOrigin-RevId: 697036283

csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs

diff --git a/csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs b/csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs
deleted file mode 100644
index 208ce1f..0000000
--- a/csharp/src/Google.Protobuf/Reflection/FeatureSetDescriptor.g.cs
+++ /dev/null
@@ -1,17 +0,0 @@
-#region Copyright notice and license
-// Protocol Buffers - Google's data interchange format
-// Copyright 2008 Google Inc.  All rights reserved.
-//
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
-#endregion
-
-namespace Google.Protobuf.Reflection;
-
-internal sealed partial class FeatureSetDescriptor
-{
-    // Canonical serialized form of the edition defaults, generated by embed_edition_defaults.
-    private const string DefaultsBase64 =
-        "ChMYhAciACoMCAEQAhgCIAMoATACChMY5wciACoMCAIQARgBIAIoATABChMY6AciDAgBEAEYASACKAEwASoAIOYHKOgH";
-}

upb/mini_descriptor/build_enum.c

diff --git a/upb/mini_descriptor/build_enum.c b/upb/mini_descriptor/build_enum.c
index 485fee2..e368ffe 100644
--- a/upb/mini_descriptor/build_enum.c
+++ b/upb/mini_descriptor/build_enum.c
@@ -31,7 +31,7 @@
 } upb_MdEnumDecoder;
 
 static size_t upb_MiniTableEnum_Size(size_t count) {
-  return sizeof(upb_MiniTableEnum) + count * sizeof(uint32_t);
+  return UPB_SIZEOF_FLEX(upb_MiniTableEnum, UPB_PRIVATE(data), count);
 }
 
 static upb_MiniTableEnum* _upb_MiniTable_AddEnumDataMember(upb_MdEnumDecoder* d,

upb/port/def.inc

diff --git a/upb/port/def.inc b/upb/port/def.inc
index 383d0cd..6e6b49c 100644
--- a/upb/port/def.inc
+++ b/upb/port/def.inc
@@ -64,6 +64,15 @@
  */
 #define UPB_PTR_AT(msg, ofs, type) ((type*)((char*)(msg) + (ofs)))
 
+// A flexible array member may have lower alignment requirements than the struct
+// overall - in that case, it can overlap with the trailing padding of the rest
+// of the struct, and a naive sizeof(base) + sizeof(flex) * count calculation
+// will not take into account that overlap, and allocate more than is required.
+#define UPB_SIZEOF_FLEX(type, member, count) \
+  (UPB_MAX(sizeof(type),                     \
+           (offsetof(type, member) +         \
+            count * (offsetof(type, member[1]) - offsetof(type, member[0])))))
+
 #define UPB_MAPTYPE_STRING 0
 
 // UPB_EXPORT: always generate a public symbol.

upb/port/undef.inc

diff --git a/upb/port/undef.inc b/upb/port/undef.inc
index f94e276..e8df37a 100644
--- a/upb/port/undef.inc
+++ b/upb/port/undef.inc
@@ -9,6 +9,7 @@
 
 #undef UPB_SIZE
 #undef UPB_PTR_AT
+#undef UPB_SIZEOF_FLEX
 #undef UPB_MAPTYPE_STRING
 #undef UPB_EXPORT
 #undef UPB_INLINE