Re: library dependencies and --as-needed

[Alan Modra <amodra at bigpond dot net dot au>]

binutils/
	* NEWS: Mention --as-needed change.
ld/
	* ld.texinfo (--as-needed): Update.
bfd/
	* elflink.c (on_needed_list): New function.
	(elf_link_add_object_symbols): Link in --as-needed libs if they
	satisfy undefined symbols in other libs.

Index: binutils/NEWS
===================================================================
RCS file: /cvs/src/src/binutils/NEWS,v
retrieving revision 1.74
diff -u -p -r1.74 NEWS
--- binutils/NEWS	13 Jan 2009 09:23:50 -0000	1.74
+++ binutils/NEWS	31 Jan 2009 10:50:36 -0000
@@ -1,5 +1,10 @@
 -*- text -*-
 
+* --as-needed now links in a dynamic library if it satisfies undefined
+  symbols in regular objects, or in other dynamic libraries.  In the
+  latter case the library is not linked if it is found in a DT_NEEDED
+  entry of one of the libraries already linked.
+
 * Add new option --use-nul-prefixed-import-tables to dlltool to allow fall-
   back to old import table generation with null element prefix.
 
Index: ld/ld.texinfo
===================================================================
RCS file: /cvs/src/src/ld/ld.texinfo,v
retrieving revision 1.227
diff -u -p -r1.227 ld.texinfo
--- ld/ld.texinfo	26 Jan 2009 15:23:39 -0000	1.227
+++ ld/ld.texinfo	31 Jan 2009 10:59:27 -0000
@@ -1093,9 +1093,11 @@ This option affects ELF DT_NEEDED tags f
 on the command line after the @option{--as-needed} option.  Normally,
 the linker will add a DT_NEEDED tag for each dynamic library mentioned
 on the command line, regardless of whether the library is actually
-needed.  @option{--as-needed} causes DT_NEEDED tags to only be emitted
-for libraries that satisfy some symbol reference from regular objects
-which is undefined at the point that the library was linked.
+needed.  @option{--as-needed} causes a DT_NEEDED tag to only be emitted
+for a library that satisfies a symbol reference from regular objects
+which is undefined at the point that the library was linked, or, if
+the library is not found in the DT_NEEDED lists of other libraries
+linked up to that point, a reference from another dynamic library.
 @option{--no-as-needed} restores the default behaviour.
 
 @kindex --add-needed
Index: bfd/elflink.c
===================================================================
RCS file: /cvs/src/src/bfd/elflink.c,v
retrieving revision 1.328
diff -u -p -r1.328 elflink.c
--- bfd/elflink.c	29 Jan 2009 16:35:03 -0000	1.328
+++ bfd/elflink.c	31 Jan 2009 07:14:55 -0000
@@ -3199,6 +3199,16 @@ elf_add_dt_needed_tag (bfd *abfd,
   return 0;
 }
 
+static bfd_boolean
+on_needed_list (const char *soname, struct bfd_link_needed_list *needed)
+{
+  for (; needed != NULL; needed = needed->next)
+    if (strcmp (soname, needed->name) == 0)
+      return TRUE;
+
+  return FALSE;
+}
+
 /* Sort symbol by value and section.  */
 static int
 elf_sort_symbol (const void *arg1, const void *arg2)
@@ -4434,8 +4444,11 @@ elf_link_add_object_symbols (bfd *abfd, 
 
 	  if (!add_needed
 	      && definition
-	      && dynsym
-	      && h->ref_regular)
+	      && ((dynsym
+		   && h->ref_regular)
+		  || (h->ref_dynamic
+		      && (elf_dyn_lib_class (abfd) & DYN_AS_NEEDED) != 0
+		      && !on_needed_list (elf_dt_name (abfd), htab->needed))))
 	    {
 	      int ret;
 	      const char *soname = elf_dt_name (abfd);

-- 
Alan Modra
Australia Development Lab, IBM