[gcc r11-11388] Objective-C, Darwin: Do not overalign CFStrings and Objective-C metadata.

[Iain D Sandoe <iains@gcc.gnu.org>]

https://gcc.gnu.org/g:88d9c5bfb17ef5c5288eb58ddc64dee7d52ecdf4

commit r11-11388-g88d9c5bfb17ef5c5288eb58ddc64dee7d52ecdf4
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Thu Jan 25 20:11:09 2024 +0000

    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.c (darwin_build_constant_cfstring): Prevent over-
            alignment of CFString constants by setting DECL_USER_ALIGN.
    
    gcc/objc/ChangeLog:
    
            * objc-next-runtime-abi-02.c (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.c (generate_strings): Likewise.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    (cherry picked from commit f74f840d35117bcaf995cee99fb2ab30c60f64f3)

Diff:
---
 gcc/config/darwin.c                    |  1 +
 gcc/objc/objc-next-runtime-abi-02.c    | 18 +++++++++++++++---
 gcc/objc/objc-runtime-shared-support.c |  4 ++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/gcc/config/darwin.c b/gcc/config/darwin.c
index ec779332544..6e887a9ba5a 100644
--- a/gcc/config/darwin.c
+++ b/gcc/config/darwin.c
@@ -3867,6 +3867,7 @@ 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.c b/gcc/objc/objc-next-runtime-abi-02.c
index 0c59299db05..cb22a773fcb 100644
--- a/gcc/objc/objc-next-runtime-abi-02.c
+++ b/gcc/objc/objc-next-runtime-abi-02.c
@@ -2251,6 +2251,7 @@ 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);
 }
 
@@ -2325,8 +2326,9 @@ 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.  */
@@ -2404,6 +2406,7 @@ 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;
@@ -2512,6 +2515,7 @@ 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;
 }
@@ -2530,13 +2534,14 @@ 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;
 }
@@ -2659,6 +2664,7 @@ 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;
 }
@@ -2870,6 +2876,7 @@ 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;
@@ -3167,6 +3174,7 @@ 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;
@@ -3434,7 +3442,6 @@ 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,
@@ -3444,6 +3451,7 @@ 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 = { ... }; */
@@ -3455,6 +3463,7 @@ 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;
 
@@ -3534,6 +3543,7 @@ 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 = { ... }; */
@@ -3545,6 +3555,7 @@ 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;
 
@@ -3719,6 +3730,7 @@ 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.c b/gcc/objc/objc-runtime-shared-support.c
index 40f506c6e75..e68e98af4dd 100644
--- a/gcc/objc/objc-runtime-shared-support.c
+++ b/gcc/objc/objc-runtime-shared-support.c
@@ -689,6 +689,7 @@ 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);
     }
 
@@ -698,6 +699,7 @@ 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);
     }
 
@@ -707,6 +709,7 @@ 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);
     }
 
@@ -716,6 +719,7 @@ 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);
     }
 }