From cddca68e972e316b06e21e04de431aa81beadb89 Mon Sep 17 00:00:00 2001
From: JCash <mwesterdahl76@gmail.com>
Date: Fri, 12 Aug 2022 12:42:55 +0200
Subject: [PATCH 1/2] Add optional support for 16 byte alignment for user data
 structs

---
 src/lj_obj.h  | 24 ++++++++++++++++++++++--
 src/luaconf.h | 10 ++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/lj_obj.h b/src/lj_obj.h
index 67e41181..c1a2097b 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -319,17 +319,37 @@ typedef struct GCstr {
 
 /* -- Userdata object ----------------------------------------------------- */
 
+#if defined(__GNUC__)
+  #define LUA_STRUCT_ALIGNED(a) __attribute__ ((aligned (a)))
+#elif defined(_MSC_VER)
+  #define LUA_STRUCT_ALIGNED(a) __declspec(align(a))
+#else
+  #warning "No struct alignment for GCudata"
+  #define LUA_STRUCT_ALIGNED(a)
+#endif
+
 /* Userdata object. Payload follows. */
-typedef struct GCudata {
+typedef struct LUA_STRUCT_ALIGNED(LUA_USERDATA_ALIGNMENT) GCudata {
   GCHeader;
   uint8_t udtype;	/* Userdata type. */
   uint8_t unused2;
   GCRef env;		/* Should be at same offset in GCfunc. */
   MSize len;		/* Size of payload. */
   GCRef metatable;	/* Must be at same offset in GCtab. */
-  uint32_t align1;	/* To force 8 byte alignment of the payload. */
+
+  uint32_t align0;      /* To force 8 byte alignment of the payload. */
+#if LUA_USERDATA_ALIGNMENT == 16
+    #ifndef LJ_GC64
+        uint64_t align1;/* To force 16 byte alignment of the payload. */
+    #endif
+#endif
+
 } GCudata;
 
+#undef LUA_STRUCT_ALIGNED
+
+LJ_STATIC_ASSERT((sizeof(GCudata) % LUA_USERDATA_ALIGNMENT) == 0);
+
 /* Userdata types. */
 enum {
   UDTYPE_USERDATA,	/* Regular userdata. */
diff --git a/src/luaconf.h b/src/luaconf.h
index e8790c1d..f676fa94 100644
--- a/src/luaconf.h
+++ b/src/luaconf.h
@@ -123,6 +123,16 @@
 #define LUA_INTFRMLEN		"l"
 #define LUA_INTFRM_T		long
 
+/* Allows for aligning the userdata struct. Valid values are 8 or 16. Default is 8.
+*/
+#if !defined(LUA_USERDATA_ALIGNMENT)
+  #define LUA_USERDATA_ALIGNMENT 8
+#endif
+
+#if !(LUA_USERDATA_ALIGNMENT == 8 || LUA_USERDATA_ALIGNMENT == 16)
+#error "Invalid LUA_USERDATA_ALIGNMENT (valid values are 8 or 16)"
+#endif
+
 /* Linkage of public API functions. */
 #if defined(LUA_BUILD_AS_DLL)
 #if defined(LUA_CORE) || defined(LUA_LIB)

From a37acfab443552a9b029caf34eda35a3f57dafae Mon Sep 17 00:00:00 2001
From: JCash <mwesterdahl76@gmail.com>
Date: Fri, 12 Aug 2022 12:45:50 +0200
Subject: [PATCH 2/2] Use LJ_ALIGN instead

---
 src/lj_obj.h | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/src/lj_obj.h b/src/lj_obj.h
index c1a2097b..c806e684 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -319,17 +319,8 @@ typedef struct GCstr {
 
 /* -- Userdata object ----------------------------------------------------- */
 
-#if defined(__GNUC__)
-  #define LUA_STRUCT_ALIGNED(a) __attribute__ ((aligned (a)))
-#elif defined(_MSC_VER)
-  #define LUA_STRUCT_ALIGNED(a) __declspec(align(a))
-#else
-  #warning "No struct alignment for GCudata"
-  #define LUA_STRUCT_ALIGNED(a)
-#endif
-
 /* Userdata object. Payload follows. */
-typedef struct LUA_STRUCT_ALIGNED(LUA_USERDATA_ALIGNMENT) GCudata {
+typedef struct LJ_ALIGN(LUA_USERDATA_ALIGNMENT) GCudata {
   GCHeader;
   uint8_t udtype;	/* Userdata type. */
   uint8_t unused2;