__attibute__((__aligned__)) for RSTRING_PTR()

For instance array.c:rb_ary_product() uses RSTRING_PTR() as an
array of int. So to avoid misaligned memory access RSTRING_PTR()
must at least be sizeof(int)-aligned.  However the type of
RSTRING_PTR() is char*, which of course can expect alignment as
much as 1.  This is a problem.

The reality is, there is no misaligned memory access because the
memory region behind RSTRING_PTR() is allocated using malloc().
Memory regions returned from malloc() are always aligned
appropriately.  So let's tell the compiler about this information.
It seems GCC, clang, and MSVC have such feature.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61827 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 8 insertions, 9 deletions

diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 6d84a6b06e..fe0ecf4622 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -853,14 +853,10 @@ enum ruby_fl_type {
     RUBY_FL_SINGLETON = RUBY_FL_USER0
 };
 
-struct RBasic {
+struct RUBY_ALIGNAS(sizeof(VALUE)) RBasic {
     VALUE flags;
     const VALUE klass;
-}
-#ifdef __GNUC__
-    __attribute__((aligned(sizeof(VALUE))))
-#endif
-;
+};
 
 VALUE rb_obj_hide(VALUE obj);
 VALUE rb_obj_reveal(VALUE obj, VALUE klass); /* do not use this API to change klass information */
@@ -953,18 +949,21 @@ enum ruby_rstring_flags {
 
     RSTRING_ENUM_END
 };
+
+typedef RUBY_ALIGNAS(sizeof(VALUE)) char ruby_aligned_char;
+
 struct RString {
     struct RBasic basic;
     union {
 	struct {
 	    long len;
-	    char *ptr;
+	    ruby_aligned_char *ptr;
 	    union {
 		long capa;
 		VALUE shared;
 	    } aux;
 	} heap;
-	char ary[RSTRING_EMBED_LEN_MAX + 1];
+	char RUBY_ALIGNAS(sizeof(VALUE)) ary[RSTRING_EMBED_LEN_MAX + 1];
     } as;
 };
 #define RSTRING_EMBED_LEN(str) \
@@ -976,7 +975,7 @@ struct RString {
      RSTRING(str)->as.heap.len)
 #define RSTRING_PTR(str) \
     (!(RBASIC(str)->flags & RSTRING_NOEMBED) ? \
-     RSTRING(str)->as.ary : \
+     (ruby_aligned_char *)RSTRING(str)->as.ary : \
      RSTRING(str)->as.heap.ptr)
 #define RSTRING_END(str) \
     (!(RBASIC(str)->flags & RSTRING_NOEMBED) ? \