[libcxx-commits] [PATCH] D128285: [libc++][AIX] Make basic_string layout compatible with earlier version

[Xing Xue via Phabricator via libcxx-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG60f7bdfd0317: [libc++][AIX] Make basic_string layout compatible with earlier version (authored by xingxue).

Changed prior to commit:
  https://reviews.llvm.org/D128285?vs=439870&id=439893#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128285/new/

https://reviews.llvm.org/D128285

Files:
  libcxx/include/__config
  libcxx/include/string


Index: libcxx/include/string
===================================================================
--- libcxx/include/string
+++ libcxx/include/string
@@ -721,10 +721,16 @@
     static const size_type __endian_factor = 2;
 #endif
 
+    // Attribute 'packed' is used to keep the layout compatible with the
+    // previous definition that did not use bit fields. This is because on
+    // some platforms bit fields have a default size rather than the actual
+    // size used, e.g., it is 4 bytes on AIX. See D128285 for details.
     struct __long
     {
-        size_type __is_long_ : 1;
-        size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
+        struct _LIBCPP_PACKED {
+            size_type __is_long_ : 1;
+            size_type __cap_ : sizeof(size_type) * CHAR_BIT - 1;
+        };
         size_type __size_;
         pointer   __data_;
     };
@@ -734,8 +740,10 @@
 
     struct __short
     {
-        unsigned char __is_long_ : 1;
-        unsigned char __size_ : 7;
+        struct _LIBCPP_PACKED {
+            unsigned char __is_long_ : 1;
+            unsigned char __size_ : 7;
+        };
         char __padding_[sizeof(value_type) - 1];
         value_type __data_[__min_cap];
     };
Index: libcxx/include/__config
===================================================================
--- libcxx/include/__config
+++ libcxx/include/__config
@@ -1176,6 +1176,12 @@
 #    define _LIBCPP_PACKED_BYTE_FOR_AIX_END /* empty */
 #  endif
 
+#  if __has_attribute(__packed__)
+#    define _LIBCPP_PACKED __attribute__((__packed__))
+#  else
+#    define _LIBCPP_PACKED
+#  endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP___CONFIG


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D128285.439893.patch
Type: text/x-patch
Size: 1657 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/libcxx-commits/attachments/20220624/c9f014f1/attachment.bin>