Objective-C, Darwin: Do not overalign CFStrings and Objective-C metadata.

We have reports of regressions in both Objective-C and Objective-C++ on
Darwin23 (macOS 14).  In some cases, these are linker warnings about the
alignment of CFString constants; in other cases the built executables
crash during runtime initialization.  The underlying issue is the same in
both cases; since the objects (CFStrings, Objective-C meta-data) are TU-
local, we are choosing to increase their alignment for efficiency - to
values greater than ABI alignment.

However, although these objects are TU-local, they are also visible to the
linker (since they are placed in specific named sections).  In many cases
the metadata can be regarded as tables of data, and thus it is expected
that these sections can be concatenated from multiple TUs and the data
treated as tabular.  In order for this to work the data cannot be allowed
to exceed ABI alignment - which leads to the crashes.

For GCC-15+ it would be nice to find a more elegant solution to this issue
(perhaps by adjusting the concept of binds-locally to exclude specific
named sections) - but I do not want to do that in stage 4.

The solution here is to force the alignment to be preserved as created by
setting DECL_USER_ALIGN on the relevant objects.

gcc/ChangeLog:

	* config/darwin.cc (darwin_build_constant_cfstring): Prevent over-
	alignment of CFString constants by setting DECL_USER_ALIGN.

gcc/objc/ChangeLog:

	* objc-next-runtime-abi-02.cc (build_v2_address_table): Prevent
	over-alignment of Objective-C metadata by setting DECL_USER_ALIGN
	on relevant variables.
	(build_v2_protocol_list_address_table): Likewise.
	(generate_v2_protocol_list): Likewise.
	(generate_v2_meth_descriptor_table): Likewise.
	(generate_v2_meth_type_list): Likewise.
	(generate_v2_property_table): Likewise.
	(generate_v2_dispatch_table): Likewise.
	(generate_v2_ivars_list): Likewise.
	(generate_v2_class_structs): Likewise.
	(build_ehtype): Likewise.
	* objc-runtime-shared-support.cc (generate_strings): Likewise.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit f74f840d35117bcaf995cee99fb2ab30c60f64f3)

diff --git a/gcc/config/darwin.cc b/gcc/config/darwin.cc
index a11095716d880736947260f2e4225d6f9e25313e..129250a48fdcdc1f246a4cce3ab0d1ea9ebe2522 100644 (file)
--- a/gcc/config/darwin.cc
+++ b/gcc/config/darwin.cc
@@ -3859,6 +3859,7 @@ darwin_build_constant_cfstring (tree str)
       /* global namespace.  */
       DECL_CONTEXT (var) = NULL_TREE;
       DECL_INITIAL (var) = constructor;
+      DECL_USER_ALIGN (var) = 1;
       lang_hooks.decls.pushdecl (var);
       rest_of_decl_compilation (var, 1, 0);
       desc->ccf_str = var;

diff --git a/gcc/objc/objc-next-runtime-abi-02.cc b/gcc/objc/objc-next-runtime-abi-02.cc
index a9b3e32b92d6e171d92bc46673e8196ea5e1a6d0..1dee05df76913417a8d2327eb53e1838787dc54f 100644 (file)
--- a/gcc/objc/objc-next-runtime-abi-02.cc
+++ b/gcc/objc/objc-next-runtime-abi-02.cc
@@ -2246,6 +2246,7 @@ build_v2_address_table (vec<tree, va_gc> *src, const char *nam, tree attr)
   DECL_PRESERVE_P (decl) = 1;
   expr = objc_build_constructor (type, initlist);
   OBJCMETA (decl, objc_meta, attr);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, expr);
 }
 
@@ -2320,8 +2321,9 @@ build_v2_protocol_list_address_table (void)
        decl = create_global_decl (objc_protocol_type, buf, /*is def=*/true);
       expr = convert (objc_protocol_type, build_fold_addr_expr (ref->refdecl));
       OBJCMETA (decl, objc_meta, meta_label_protocollist);
-      finish_var_decl (decl, expr);
       DECL_PRESERVE_P (decl) = 1;
+      DECL_USER_ALIGN (decl) = 1;
+      finish_var_decl (decl, expr);
     }
 
     /* TODO: delete the vec.  */
@@ -2399,6 +2401,7 @@ generate_v2_protocol_list (tree i_or_p, tree klass_ctxt)
   /* ObjC2 puts all these in the base section.  */
   OBJCMETA (refs_decl, objc_meta, meta_base);
   DECL_PRESERVE_P (refs_decl) = 1;
+  DECL_USER_ALIGN (refs_decl) = 1;
   finish_var_decl (refs_decl,
                   objc_build_constructor (TREE_TYPE (refs_decl),initlist));
   return refs_decl;
@@ -2507,6 +2510,7 @@ generate_v2_meth_descriptor_table (tree chain, tree protocol,
   CONSTRUCTOR_APPEND_ELT (v, NULL_TREE, initlist);
   /* Get into the right section.  */
   OBJCMETA (decl, objc_meta, attr);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, objc_build_constructor (method_list_template, v));
   return decl;
 }
@@ -2525,13 +2529,14 @@ generate_v2_meth_type_list (vec<tree>& all_meths, tree protocol,
            IDENTIFIER_POINTER (PROTOCOL_NAME (protocol)));
   tree decl = start_var_decl (list_type, nam);
   free (nam);
-  OBJCMETA (decl, objc_meta, meta_base);
   vec<constructor_elt, va_gc> *v = NULL;
 
   for (unsigned i = 0; i < size; ++i)
     CONSTRUCTOR_APPEND_ELT (v, NULL_TREE,
                            add_objc_string (METHOD_ENCODING (all_meths[i]),
                                             meth_var_types));
+  OBJCMETA (decl, objc_meta, meta_base);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, objc_build_constructor (list_type, v));
   return decl;
 }
@@ -2654,6 +2659,7 @@ generate_v2_property_table (tree context, tree klass_ctxt)
   CONSTRUCTOR_APPEND_ELT (inits, NULL_TREE, initlist);
 
   OBJCMETA (decl, objc_meta, meta_base);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, objc_build_constructor (TREE_TYPE (decl), inits));
   return decl;
 }
@@ -2865,6 +2871,7 @@ generate_v2_dispatch_table (tree chain, const char *name, tree attr)
   CONSTRUCTOR_APPEND_ELT (v, NULL_TREE, initlist);
 
   OBJCMETA (decl, objc_meta, attr);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl,
                   objc_build_constructor (TREE_TYPE (decl), v));
   return decl;
@@ -3162,6 +3169,7 @@ generate_v2_ivars_list (tree chain, const char *name, tree attr, tree templ)
                          build_int_cst (integer_type_node, size));
   CONSTRUCTOR_APPEND_ELT (inits, NULL_TREE, initlist);
   OBJCMETA (decl, objc_meta, attr);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, objc_build_constructor (TREE_TYPE (decl), inits));
   generating_instance_variables = 0;
   return decl;
@@ -3429,7 +3437,6 @@ generate_v2_class_structs (struct imp_entry *impent)
   decl = start_var_decl (objc_v2_class_ro_template,
                         newabi_append_ro (IDENTIFIER_POINTER
                                                (DECL_NAME (metaclass_decl))));
-
   /* TODO: ivarLayout needs t be built.  */
   initlist =
        build_v2_class_ro_t_initializer (TREE_TYPE (decl), name_expr,
@@ -3439,6 +3446,7 @@ generate_v2_class_structs (struct imp_entry *impent)
                                        class_ivars, NULL_TREE);
   /* The ROs sit in the default const section.  */
   OBJCMETA (decl, objc_meta, meta_base);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, initlist);
 
   /* static struct class_t _OBJC_METACLASS_Foo = { ... }; */
@@ -3450,6 +3458,7 @@ generate_v2_class_structs (struct imp_entry *impent)
                                      build_fold_addr_expr (UOBJC_V2_CACHE_decl),
                                      build_fold_addr_expr (UOBJC_V2_VTABLE_decl));
   /* The class section attributes are set when they are created.  */
+  DECL_USER_ALIGN (metaclass_decl) = 1;
   finish_var_decl (metaclass_decl, initlist);
   impent->meta_decl = metaclass_decl;
 
@@ -3529,6 +3538,7 @@ generate_v2_class_structs (struct imp_entry *impent)
                                         inst_ivars, props);
   /* The ROs sit in the default const section.  */
   OBJCMETA (decl, objc_meta, meta_base);
+  DECL_USER_ALIGN (decl) = 1;
   finish_var_decl (decl, initlist);
 
   /* static struct class_t _OBJC_CLASS_Foo = { ... }; */
@@ -3540,6 +3550,7 @@ generate_v2_class_structs (struct imp_entry *impent)
                                        build_fold_addr_expr (UOBJC_V2_VTABLE_decl));
 
   /* The class section attributes are set when they are created.  */
+  DECL_USER_ALIGN (class_decl) = 1;
   finish_var_decl (class_decl, initlist);
   impent->class_decl = class_decl;
 
@@ -3714,6 +3725,7 @@ build_ehtype (tree name, const char *eh_name, bool weak)
     DECL_WEAK (ehtype_decl) = 1;
   inits = objc2_build_ehtype_initializer (name_expr, class_name_expr);
   OBJCMETA (ehtype_decl, objc_meta, meta_ehtype);
+  DECL_USER_ALIGN (ehtype_decl) = 1;
   finish_var_decl (ehtype_decl, inits);
   return ehtype_decl;
 }

diff --git a/gcc/objc/objc-runtime-shared-support.cc b/gcc/objc/objc-runtime-shared-support.cc
index 75c28fbdc5ce0e3e0046484ec1e67d7a93d7c833..074e418abd6557a37955c74a12bb3685ac4c950f 100644 (file)
--- a/gcc/objc/objc-runtime-shared-support.cc
+++ b/gcc/objc/objc-runtime-shared-support.cc
@@ -684,6 +684,7 @@ generate_strings (void)
       decl = TREE_PURPOSE (chain);
       string_expr = my_build_string (IDENTIFIER_LENGTH (string) + 1,
                                     IDENTIFIER_POINTER (string));
+      DECL_USER_ALIGN (decl) = 1;
       finish_var_decl (decl, string_expr);
     }
 
@@ -693,6 +694,7 @@ generate_strings (void)
       decl = TREE_PURPOSE (chain);
       string_expr = my_build_string (IDENTIFIER_LENGTH (string) + 1,
                                     IDENTIFIER_POINTER (string));
+      DECL_USER_ALIGN (decl) = 1;
       finish_var_decl (decl, string_expr);
     }
 
@@ -702,6 +704,7 @@ generate_strings (void)
       decl = TREE_PURPOSE (chain);
       string_expr = my_build_string (IDENTIFIER_LENGTH (string) + 1,
                                     IDENTIFIER_POINTER (string));
+      DECL_USER_ALIGN (decl) = 1;
       finish_var_decl (decl, string_expr);
     }
 
@@ -711,6 +714,7 @@ generate_strings (void)
       decl = TREE_PURPOSE (chain);
       string_expr = my_build_string (IDENTIFIER_LENGTH (string) + 1,
                                     IDENTIFIER_POINTER (string));
+      DECL_USER_ALIGN (decl) = 1;
       finish_var_decl (decl, string_expr);
     }
 }