* i386/winnt.c (i386_pe_valid_decl_attribute_p): Recognize

        shared as a valid attribute.
        * i386/cygwin.h (ASM_OUTPUT_SECTION): Handle shared attribute.
        * extend.texi: Document `shared' variable attribute.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@29404 138bc75d-0d04-0410-961f-82ee72b054a4

4 files changed, 43 insertions, 1 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 9e0f1f7e3b7..6a6f65824e0 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+Tue Sep 14 04:03:44 1999  Mumit Khan  <khan@xraylith.wisc.edu>
+
+	* i386/winnt.c (i386_pe_valid_decl_attribute_p): Recognize
+	shared as a valid attribute.
+	* i386/cygwin.h (ASM_OUTPUT_SECTION): Handle shared attribute.
+	* extend.texi: Document `shared' variable attribute.
+
 Tue Sep 14 04:01:46 1999  Loren Rittle  <ljrittle@acm.org>
 
 	* configure.in: Handle --enable-threads on FreeBSD.
diff --git a/gcc/config/i386/cygwin.h b/gcc/config/i386/cygwin.h
index a6e967f1525..023f4b0221b 100644
--- a/gcc/config/i386/cygwin.h
+++ b/gcc/config/i386/cygwin.h
@@ -405,7 +405,14 @@ do {									\
   else if (DECL && DECL_READONLY_SECTION (DECL, RELOC))			\
     type = SECT_RO, mode = "";						\
   else									\
-    type = SECT_RW, mode = "w";						\
+    {									\
+      type = SECT_RW;							\
+      if (TREE_CODE (DECL) == VAR_DECL					\
+          && lookup_attribute ("shared", DECL_MACHINE_ATTRIBUTES (DECL))) \
+        mode = "ws";							\
+      else								\
+        mode = "w";							\
+    }									\
 									\
   if (s == 0)								\
     {									\
diff --git a/gcc/config/i386/winnt.c b/gcc/config/i386/winnt.c
index bda9311a42a..2c2ce763359 100644
--- a/gcc/config/i386/winnt.c
+++ b/gcc/config/i386/winnt.c
@@ -56,6 +56,8 @@ i386_pe_valid_decl_attribute_p (decl, attributes, attr, args)
 	return 1;
       if (is_attribute_p ("dllimport", attr))
 	return 1;
+      if (is_attribute_p ("shared", attr))
+	return TREE_CODE (decl) == VAR_DECL;
     }
 
   return ix86_valid_decl_attribute_p (decl, attributes, attr, args);
diff --git a/gcc/extend.texi b/gcc/extend.texi
index 5b5f3b116c6..4ec451d3373 100644
--- a/gcc/extend.texi
+++ b/gcc/extend.texi
@@ -2015,6 +2015,32 @@ attribute is not available on all platforms.
 If you need to map the entire contents of a module to a particular
 section, consider using the facilities of the linker instead.
 
+@item shared
+@cindex @code{shared} variable attribute
+On Windows NT, in addition to nputting variable definitions in a named 
+section, the section can also be shared among all running copies of an 
+executable or DLL. For example, this small program defines shared data 
+by putting it in a named section "shared" and marking the section 
+shareable:
+
+@smallexample
+int foo __attribute__((section ("shared"), shared)) = 0;
+
+int
+main()
+@{
+  /* Read and write foo. All running copies see the same value. */
+  return 0;
+@}
+@end smallexample
+
+@noindent
+You may only use the @code{shared} attribute along with @code{section}
+attribute with a fully initialized global definition because of the way 
+linkers work.  See @code{section} attribute for more information.
+
+The @code{shared} attribute is only available on Windows NT.
+
 @item transparent_union
 This attribute, attached to a function parameter which is a union, means
 that the corresponding argument may have the type of any union member,