Applied patch series for LD plugin interface (six parts).

[PATCH] Add infrastructure for plugin API; functionality to follow.

    include/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 1/6).
	* plugin-api.h (LDPT_GNU_LD_VERSION): New ld_plugin_tag enum member.

    ld/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 1/6).
	* configure.in: Add AC_CHECKs for file io and dlfcn headers and
	functions and AC_SEARCH for -ldl.
	(enable_plugins): New shell variable set if above tests find dlopen
	functionality.
	(ENABLE_PLUGINS): Add related automake conditional.
	* configure: Regenerate.
	* config.in: Likewise.
	* Makefile.am (PLUGIN_C): Declare plugin C source file, conditional
	on ENABLE_PLUGINS being defined.
	(PLUGIN_H): Likewise for header file.
	(PLUGIN_OBJECT): Likewise for object file.
	(PLUGIN_CFLAGS): Likewise -D flag required to compile plugin support.
	(AM_CPPFLAGS): Use PLUGIN_CFLAGS.
	(CFILES): Use PLUGIN_C.
	(HFILES): Use PLUGIN_H.
	(OFILES): Use PLUGIN_OBJECT.
	(ld_new_SOURCES): Use PLUGIN_C.
	(noinst_LTLIBRARIES)[ENABLE_PLUGINS]: Declare test plugin.
	(libldtestplug_la_SOURCES)[ENABLE_PLUGINS]: Add automake definition
	for test plugin.
	(libldtestplug_la_CFLAGS)[ENABLE_PLUGINS]: Likewise.
	(libldtestplug_la_LDFLAGS)[ENABLE_PLUGINS]: Likewise.
	* Makefile.in: Regenerate.
	* sysdep.h: Include stdarg.h, unistd.h and one of fcntl.h or
	sys/file.h where available.  Include dlfcn.h when ENABLE_PLUGINS.
	(O_RDONLY): Supply default definition likewise to bfd's sysdep.h
	(O_WRONLY): Likewise.
	(O_RDWR): Likewise.
	(O_ACCMODE): Likewise.
	(O_BINARY): Likewise.
	(SEEK_SET): Likewise.
	(SEEK_CUR): Likewise.
	(SEEK_END): Likewise.
	* ldmisc.c (vfinfo): Make non-static.  Add %p format char.
	* ldmisc.h (vfinfo): Declare extern prototype.
	* lexsup.c (enum option_values)[ENABLE_PLUGINS]: Add new entries for
	OPTION_PLUGIN and OPTION_PLUGIN_OPT.
	(ld_options[])[ENABLE_PLUGINS]: Add option data for the above two.
	(parse_args)[ENABLE_PLUGINS]: Handle them, and load all plugins once
	option parsing is complete.
	* ldmain.c (main)[ENABLE_PLUGINS]: Call plugin cleanup hooks just
	after lang_finish.
	* plugin.c: New source file.
	* plugin.h: Likewise new header.
	* testplug.c: New source file.

    ld/testsuite/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 1/6).
	* ld-bootstrap/bootstrap.exp: Skip static tests also if LD plugins
	are enabled.
	* lib/ld-lib.exp (proc regexp_diff): Extend verbose debug output.
	(proc set_file_contents): Write a file with the supplied content.
	(run_ld_link_tests): Add new 'ld' action to test linker output.
	(proc check_plugin_api_available): Return true if linker under test
	supports the plugin API.
	* ld-plugin/func.c: New test source file.
	* ld-plugin/main.c: Likewise.
	* ld-plugin/text.c: Likewise.
	* ld-plugin/plugin-1.d: New dump test output pattern script.
	* ld-plugin/plugin-2.d: Likewise.
	* ld-plugin/plugin-3.d: Likewise.
	* ld-plugin/plugin-4.d: Likewise.
	* ld-plugin/plugin-5.d: Likewise.
	* ld-plugin/plugin.exp: New test control script.
---
[PATCH] Implement claim file and all symbols read hooks and add symbols callback.

  ld/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 2/6).
	* ldfile.c (ldfile_try_open_bfd)[ENABLE_PLUGINS]: Don't return early
	during compat checks if they pass, instead offer any successfully
	opened and accepted file to the plugin claim file hooks chain.  Create
	a dummy bfd to accept symbols added by the plugin, if the plugin
	claims the file.
	* ldlang.c (lang_process)[ENABLE_PLUGINS]: Call plugin all symbols
	read hook chain before ldemul_after_open.
	* ldlang.h (struct lang_input_statement_struct): Add new single-bit
	'claimed' flag.
	* plugin.c (IRONLY_SUFFIX): New macro for dummy bfd file suffix.
	(IRONLY_SUFFIX_LEN): Length of the above string.
	(plugin_get_ir_dummy_bfd): New function to create the dummy bfd used
	to store symbols for ir-only files.
	(is_ir_dummy_bfd): New function to check if a bfd is ir-only.
	(asymbol_from_plugin_symbol): New function converts symbol formats.
	(add_symbols): Call it to convert plugin syms to bfd syms and add
	them to the dummy bfd.
	* plugin.h: Add missing include guards.
	(plugin_get_ir_dummy_bfd): Add prototype.
	(is_ir_dummy_bfd): Likewise.
	* testplug.c (TV_MESSAGE): New helper macro.
	(struct claim_file): New struct.
	(claim_file_t): New typedef.
	(tag_names[]): Make static and const.
	(claimfiles_list): New variable.
	(claimfiles_tail_chain_ptr): Likewise.
	(last_claimfile): Likewise.
	(record_claim_file): Record a file to claim on a singly-linked list.
	(parse_symdefstr): Parse an ASCII representation of a symbol from a
	plugin option into the fields of a struct ld_plugin_symbol.
	(record_claimed_file_symbol):  Use it to parse plugin option for
	adding a symbol.
	(parse_option): Parse claim file and add symbol options.
	(dump_tv_tag): Use TV_MESSAGE.
	(onload): Likewise.
	(onclaim_file): Make static.  Use TV_MESSAGE.  Scan list of files to
	claim and claim this file if required, adding any symbols specified.
	(onall_symbols_read): Make static and use TV_MESSAGE.
	(oncleanup): Likewise.

  ld/testsuite/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 2/6).
	* ld-plugin/plugin-3.d: Enable regexes for new functionality.
	* ld-plugin/plugin-5.d: Likewise.
	* ld-plugin/plugin-6.d: New testcase.
	* ld-plugin/plugin-7.d: Likewise.
	* ld-plugin/plugin.exp: Use 'nm' on compiled test objects to determine
	whether symbols in plugin arguments need an underscore prefix.  Add
	new plugin-6.d and plugin-7.d testcases.
---
[PATCH] Implement get symbols callback.

  ld/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 3/6).
	* ldmain.c (notice)[ENABLE_PLUGINS]: Call plugin_notice.
	* plugin.c (non_ironly_hash): Add new bfd hash table.
	(plugin_load_plugins): Exit early if no plugins to load.  If plugins
	do load successfully, set notice_all flag in link info.
	(get_symbols): Implement.
	(plugin_load_plugins): Exit early if no plugins to load, else after
	loading plugins successfully enable notice_all mode.
	(init_non_ironly_hash): Lazily init non_ironly_hash table.
	(plugin_notice): Record symbols referenced from non-IR files in the
	non_ironly_hash.  Suppress tracing, cref generation and nocrossrefs
	tracking for symbols from dummy IR bfds.
	* plugin.h: Fix formatting.
	(plugin_notice): Add prototype.
	* testplug.c (dumpresolutions): New global var.
	(parse_options): Accept "dumpresolutions".
	(onall_symbols_read): Get syms and dump resolutions if it was given.

  ld/testsuite/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 3/6).
	* ld-plugin/plugin-8.d: New testcase.
	* ld-plugin/plugin.exp: Invoke it.
---
[PATCH] Implement add input file, add input lib and set extra lib path callbacks.

  ld/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 4/6).
	* ldlang.c (lang_process)[ENABLE_PLUGINS]: Move invocation of
	plugin_call_all_symbols_read to before setting of gc_sym_list, and
	open any new input files that may have been added during it.
	* ldmain.c (multiple_definition)[ENABLE_PLUGINS]: Call out to
	plugin_multiple_definition and let it have first say over what to do
	with the clashing definitions.
	* plugin.c (no_more_claiming): New boolean variable.
	(plugin_cached_allow_multiple_defs): Likewise.
	(add_input_file): Implement.
	(add_input_library): Likewise.
	(set_extra_library_path): Likewise.
	(plugin_call_claim_file): Don't do anything when no_more_claiming set.
	(plugin_call_all_symbols_read): Set it.  Disable link info
	"allow_multiple_definition" flag, but cache its value.
	(plugin_multiple_definition): New function.
	* plugin.h (plugin_multiple_definition): Add prototype.
	* testplug.c (addfile_enum_t): New enumerated typedef.
	(add_file_t): New struct typedef.
	(addfiles_list): New variable.
	(addfiles_tail_chain_ptr): Likewise.
	(record_add_file): New function.
	(parse_option): Parse "add:", "lib:" and "dir:" options and call it.
	(onall_symbols_read): Iterate the list of new files, libs and dirs,
	adding them.

  ld/testsuite/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 4/6).
	* ld-plugin/plugin-9.d: New testcase.
	* ld-plugin/plugin.exp: Invoke it.
---
[PATCH] Add ELF symbol visibility support to plugin interface.

  ld/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 5/6).
	* plugin.c (asymbol_from_plugin_symbol): If the bfd is an ELF bfd,
	find the elf symbol data and set the visibility in the st_other field.

  ld/testsuite/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 5/6).
	* ld-plugin/plugin-ignore.d: New dump test control script.
	* ld-plugin/plugin-vis-1.d: Likewise.
	* ld-plugin/plugin.exp: Add list of ELF-only tests and run them if
	testing on an ELF target.
---
[PATCH] Add archive support to plugin interface.

  bfd/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 6/6).
	* aoutx.h (aout_link_check_ar_symbols): Take new "subsbfd" reference
	parameter and pass it when invoking add_archive_element callback.
	(aout_link_check_archive_element): Handle substitute bfd if it
	was set during add_archive_element callback in the above.
	* cofflink.c (coff_link_check_ar_symbols): Take new "subsbfd" reference
	parameter and pass it when invoking add_archive_element callback.
	(coff_link_check_archive_element): Handle substitute bfd if it
	was set during add_archive_element callback in the above.
	* ecoff.c (read_ext_syms_and_strs): New function holds symbol-reading
	code factored-out from ecoff_link_check_archive_element.
	(reread_ext_syms_and_strs): Clear old symbols and call it.
	(ecoff_link_check_archive_element):  Use the above.  Handle substitute
	BFD if one is set by add_archive_element callback.
	(ecoff_link_add_archive_symbols): Likewise allow bfd substitution.
	* elflink.c (elf_link_add_archive_symbols): Likewise.
	* linker.c (generic_link_check_archive_element): Likewise.
	* pdp11.c (aout_link_check_ar_symbols): Take new "subsbfd" reference
	parameter and pass it when invoking add_archive_element callback.
	(aout_link_check_archive_element): Handle substitute bfd if it was
	set during add_archive_element callback in the above.
	* vms-alpha.c (alpha_vms_link_add_archive_symbols): Handle substitute
	BFD if one is set by add_archive_element callback.
	* xcofflink.c (xcoff_link_check_dynamic_ar_symbols): Take new "subsbfd"
	reference parameter and pass it when invoking add_archive_element
	callback.
	(xcoff_link_check_ar_symbols): Likewise.
	(xcoff_link_check_archive_element): Handle bfd substitution if it was
	set by callback in the above.

  include/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 6/6).
	* bfdlink.h (struct_bfd_link_callbacks): Document new argument
	to add_archive_element callback used to return a replacement bfd which
	is to be added to the hash table in place of the original element.

  ld/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 6/6).
	* ldlang.c (load_symbols): Handle bfd subsitution when calling the
	add_archive_element callback.
	* ldmain.c (add_archive_element)[ENABLE_PLUGINS]: Offer the archive
	member to the plugins and if claimed set "subsbfd" output parameter to
	point to the dummy IR-only BFD.

  ld/testsuite/ChangeLog:

2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com>

	Apply LD plugin patch series (part 6/6).
	* ld-plugin/plugin-10.d: New dump test control script.
	* ld-plugin/plugin-11.d: Likewise.
	* ld-plugin/plugin.exp: Run them.
---

9 files changed, 212 insertions, 66 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 2e18e8c..7981dce 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,35 @@
+2010-10-14  Dave Korn  <dave.korn.cygwin@gmail.com> 
+
+	Apply LD plugin patch series (part 6/6).
+	* aoutx.h (aout_link_check_ar_symbols): Take new "subsbfd" reference
+	parameter and pass it when invoking add_archive_element callback.
+	(aout_link_check_archive_element): Handle substitute bfd if it
+	was set during add_archive_element callback in the above.
+	* cofflink.c (coff_link_check_ar_symbols): Take new "subsbfd" reference
+	parameter and pass it when invoking add_archive_element callback.
+	(coff_link_check_archive_element): Handle substitute bfd if it
+	was set during add_archive_element callback in the above.
+	* ecoff.c (read_ext_syms_and_strs): New function holds symbol-reading
+	code factored-out from ecoff_link_check_archive_element.
+	(reread_ext_syms_and_strs): Clear old symbols and call it.
+	(ecoff_link_check_archive_element):  Use the above.  Handle substitute
+	BFD if one is set by add_archive_element callback.
+	(ecoff_link_add_archive_symbols): Likewise allow bfd substitution.
+	* elflink.c (elf_link_add_archive_symbols): Likewise.
+	* linker.c (generic_link_check_archive_element): Likewise.
+	* pdp11.c (aout_link_check_ar_symbols): Take new "subsbfd" reference
+	parameter and pass it when invoking add_archive_element callback.
+	(aout_link_check_archive_element): Handle substitute bfd if it was
+	set during add_archive_element callback in the above.
+	* vms-alpha.c (alpha_vms_link_add_archive_symbols): Handle substitute
+	BFD if one is set by add_archive_element callback.
+	* xcofflink.c (xcoff_link_check_dynamic_ar_symbols): Take new "subsbfd"
+	reference parameter and pass it when invoking add_archive_element
+	callback.
+	(xcoff_link_check_ar_symbols): Likewise.
+	(xcoff_link_check_archive_element): Handle bfd substitution if it was
+	set by callback in the above.
+
 2010-10-11  Alan Modra  <amodra@gmail.com>
 
 	* elf32-frv.c (elf32_frv_relocate_section): Set "name" for global syms.
diff --git a/bfd/aoutx.h b/bfd/aoutx.h
index 11598a0..efa9d47 100644
--- a/bfd/aoutx.h
+++ b/bfd/aoutx.h
@@ -3210,7 +3210,8 @@ aout_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
 static bfd_boolean
 aout_link_check_ar_symbols (bfd *abfd,
 			    struct bfd_link_info *info,
-			    bfd_boolean *pneeded)
+			    bfd_boolean *pneeded,
+			    bfd **subsbfd)
 {
   struct external_nlist *p;
   struct external_nlist *pend;
@@ -3304,7 +3305,8 @@ aout_link_check_ar_symbols (bfd *abfd,
 		continue;
 	    }
 
-	  if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+	  if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 	    return FALSE;
 	  *pneeded = TRUE;
 	  return TRUE;
@@ -3331,9 +3333,8 @@ aout_link_check_ar_symbols (bfd *abfd,
 			 outside BFD.  We assume that we should link
 			 in the object file.  This is done for the -u
 			 option in the linker.  */
-		      if (! (*info->callbacks->add_archive_element) (info,
-								     abfd,
-								     name))
+		      if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 			return FALSE;
 		      *pneeded = TRUE;
 		      return TRUE;
@@ -3381,7 +3382,8 @@ aout_link_check_ar_symbols (bfd *abfd,
 	     it if the current link symbol is common.  */
 	  if (h->type == bfd_link_hash_undefined)
 	    {
-	      if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+	      if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 		return FALSE;
 	      *pneeded = TRUE;
 	      return TRUE;
@@ -3402,15 +3404,21 @@ aout_link_check_archive_element (bfd *abfd,
 				 struct bfd_link_info *info,
 				 bfd_boolean *pneeded)
 {
+  bfd *subsbfd = NULL;
+
   if (! aout_get_external_symbols (abfd))
     return FALSE;
 
-  if (! aout_link_check_ar_symbols (abfd, info, pneeded))
+  if (! aout_link_check_ar_symbols (abfd, info, pneeded, &subsbfd))
     return FALSE;
 
   if (*pneeded)
     {
-      if (! aout_link_add_symbols (abfd, info))
+      /* Potentially, the add_archive_element hook may have set a
+	 substitute BFD for us.  */
+      if (subsbfd && !aout_get_external_symbols (subsbfd))
+	return FALSE;
+      if (! aout_link_add_symbols (subsbfd ? subsbfd : abfd, info))
 	return FALSE;
     }
 
diff --git a/bfd/cofflink.c b/bfd/cofflink.c
index a29b687..a28d396 100644
--- a/bfd/cofflink.c
+++ b/bfd/cofflink.c
@@ -197,7 +197,8 @@ coff_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
 static bfd_boolean
 coff_link_check_ar_symbols (bfd *abfd,
 			    struct bfd_link_info *info,
-			    bfd_boolean *pneeded)
+			    bfd_boolean *pneeded,
+			    bfd **subsbfd)
 {
   bfd_size_type symesz;
   bfd_byte *esym;
@@ -243,7 +244,8 @@ coff_link_check_ar_symbols (bfd *abfd,
 	  if (h != (struct bfd_link_hash_entry *) NULL
 	      && h->type == bfd_link_hash_undefined)
 	    {
-	      if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+	      if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 		return FALSE;
 	      *pneeded = TRUE;
 	      return TRUE;
@@ -267,14 +269,23 @@ coff_link_check_archive_element (bfd *abfd,
 				 struct bfd_link_info *info,
 				 bfd_boolean *pneeded)
 {
+  bfd *subsbfd = NULL;
+
   if (! _bfd_coff_get_external_symbols (abfd))
     return FALSE;
 
-  if (! coff_link_check_ar_symbols (abfd, info, pneeded))
+  if (! coff_link_check_ar_symbols (abfd, info, pneeded, &subsbfd))
+    return FALSE;
+
+  /* Potentially, the add_archive_element hook may have set a
+     substitute BFD for us.  */
+  if (*pneeded
+      && subsbfd
+      && ! _bfd_coff_get_external_symbols (subsbfd))
     return FALSE;
 
   if (*pneeded
-      && ! coff_link_add_symbols (abfd, info))
+      && ! coff_link_add_symbols (subsbfd ? subsbfd : abfd, info))
     return FALSE;
 
   if ((! info->keep_memory || ! *pneeded)
diff --git a/bfd/ecoff.c b/bfd/ecoff.c
index af9d7d6..37003d2 100644
--- a/bfd/ecoff.c
+++ b/bfd/ecoff.c
@@ -3509,6 +3509,58 @@ ecoff_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
   return FALSE;
 }
 
+/* Factored out from ecoff_link_check_archive_element.  */
+
+static bfd_boolean
+read_ext_syms_and_strs (HDRR **symhdr, bfd_size_type *external_ext_size,
+	bfd_size_type *esize, void **external_ext, char **ssext, bfd *abfd,
+	const struct ecoff_backend_data * const backend)
+{
+  if (! ecoff_slurp_symbolic_header (abfd))
+    return FALSE;
+
+  /* If there are no symbols, we don't want it.  */
+  if (bfd_get_symcount (abfd) == 0)
+    return TRUE;
+
+  *symhdr = &ecoff_data (abfd)->debug_info.symbolic_header;
+
+  *external_ext_size = backend->debug_swap.external_ext_size;
+  *esize = (*symhdr)->iextMax * *external_ext_size;
+  *external_ext = bfd_malloc (*esize);
+  if (*external_ext == NULL && *esize != 0)
+    return FALSE;
+
+  if (bfd_seek (abfd, (file_ptr) (*symhdr)->cbExtOffset, SEEK_SET) != 0
+      || bfd_bread (*external_ext, *esize, abfd) != *esize)
+    return FALSE;
+
+  *ssext = (char *) bfd_malloc ((bfd_size_type) (*symhdr)->issExtMax);
+  if (*ssext == NULL && (*symhdr)->issExtMax != 0)
+    return FALSE;
+
+  if (bfd_seek (abfd, (file_ptr) (*symhdr)->cbSsExtOffset, SEEK_SET) != 0
+      || (bfd_bread (*ssext, (bfd_size_type) (*symhdr)->issExtMax, abfd)
+	  != (bfd_size_type) (*symhdr)->issExtMax))
+    return FALSE;
+  return TRUE;
+}
+
+static bfd_boolean
+reread_ext_syms_and_strs (HDRR **symhdr, bfd_size_type *external_ext_size,
+	bfd_size_type *esize, void **external_ext, char **ssext, bfd *abfd,
+	const struct ecoff_backend_data * const backend)
+{
+  if (*external_ext != NULL)
+    free (*external_ext);
+  *external_ext = NULL;
+  if (*ssext != NULL)
+    free (*ssext);
+  *ssext = NULL;
+  return read_ext_syms_and_strs (symhdr, external_ext_size, esize,
+				external_ext, ssext, abfd, backend);
+}
+
 /* This is called if we used _bfd_generic_link_add_archive_symbols
    because we were not dealing with an ECOFF archive.  */
 
@@ -3530,35 +3582,15 @@ ecoff_link_check_archive_element (bfd *abfd,
 
   *pneeded = FALSE;
 
-  if (! ecoff_slurp_symbolic_header (abfd))
+  /* Read in the external symbols and external strings.  */
+  if (!read_ext_syms_and_strs (&symhdr, &external_ext_size, &esize,
+	&external_ext, &ssext, abfd, backend))
     goto error_return;
 
   /* If there are no symbols, we don't want it.  */
   if (bfd_get_symcount (abfd) == 0)
     goto successful_return;
 
-  symhdr = &ecoff_data (abfd)->debug_info.symbolic_header;
-
-  /* Read in the external symbols and external strings.  */
-  external_ext_size = backend->debug_swap.external_ext_size;
-  esize = symhdr->iextMax * external_ext_size;
-  external_ext = bfd_malloc (esize);
-  if (external_ext == NULL && esize != 0)
-    goto error_return;
-
-  if (bfd_seek (abfd, (file_ptr) symhdr->cbExtOffset, SEEK_SET) != 0
-      || bfd_bread (external_ext, esize, abfd) != esize)
-    goto error_return;
-
-  ssext = (char *) bfd_malloc ((bfd_size_type) symhdr->issExtMax);
-  if (ssext == NULL && symhdr->issExtMax != 0)
-    goto error_return;
-
-  if (bfd_seek (abfd, (file_ptr) symhdr->cbSsExtOffset, SEEK_SET) != 0
-      || (bfd_bread (ssext, (bfd_size_type) symhdr->issExtMax, abfd)
-	  != (bfd_size_type) symhdr->issExtMax))
-    goto error_return;
-
   /* Look through the external symbols to see if they define some
      symbol that is currently undefined.  */
   ext_ptr = (char *) external_ext;
@@ -3568,6 +3600,7 @@ ecoff_link_check_archive_element (bfd *abfd,
       EXTR esym;
       bfd_boolean def;
       const char *name;
+      bfd *subsbfd;
       struct bfd_link_hash_entry *h;
 
       (*swap_ext_in) (abfd, (void *) ext_ptr, &esym);
@@ -3612,9 +3645,18 @@ ecoff_link_check_archive_element (bfd *abfd,
 	continue;
 
       /* Include this element.  */
-      if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+      subsbfd = NULL;
+      if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, &subsbfd))
+	goto error_return;
+      /* Potentially, the add_archive_element hook may have set a
+	 substitute BFD for us.  */
+      if (subsbfd
+	  && !reread_ext_syms_and_strs (&symhdr, &external_ext_size, &esize,
+				&external_ext, &ssext, subsbfd, backend))
 	goto error_return;
-      if (! ecoff_link_add_externals (abfd, info, external_ext, ssext))
+      if (! ecoff_link_add_externals (subsbfd ? subsbfd : abfd, info,
+				external_ext, ssext))
 	goto error_return;
 
       *pneeded = TRUE;
@@ -3691,6 +3733,7 @@ ecoff_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
       unsigned int file_offset;
       const char *name;
       bfd *element;
+      bfd *subsbfd;
 
       h = *pundef;
 
@@ -3777,9 +3820,13 @@ ecoff_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
       /* Unlike the generic linker, we know that this element provides
 	 a definition for an undefined symbol and we know that we want
 	 to include it.  We don't need to check anything.  */
-      if (! (*info->callbacks->add_archive_element) (info, element, name))
+      subsbfd = NULL;
+      if (! (*info->callbacks->add_archive_element)
+					(info, element, name, &subsbfd))
 	return FALSE;
-      if (! ecoff_link_add_object_symbols (element, info))
+      /* Potentially, the add_archive_element hook may have set a
+	 substitute BFD for us.  */
+      if (! ecoff_link_add_object_symbols (subsbfd ? subsbfd : element, info))
 	return FALSE;
 
       pundef = &(*pundef)->u.undef.next;
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 41fba17..6d37dc8 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -5011,6 +5011,7 @@ elf_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
 	{
 	  struct elf_link_hash_entry *h;
 	  bfd *element;
+	  bfd *subsbfd = NULL;
 	  struct bfd_link_hash_entry *undefs_tail;
 	  symindex mark;
 
@@ -5073,10 +5074,12 @@ elf_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
 
 	  undefs_tail = info->hash->undefs_tail;
 
-	  if (! (*info->callbacks->add_archive_element) (info, element,
-							 symdef->name))
+	  if (! (*info->callbacks->add_archive_element)
+				(info, element, symdef->name, &subsbfd))
 	    goto error_return;
-	  if (! bfd_link_add_symbols (element, info))
+	  /* Potentially, the add_archive_element hook may have set a
+	     substitute BFD for us.  */
+	  if (! bfd_link_add_symbols (subsbfd ? subsbfd : element, info))
 	    goto error_return;
 
 	  /* If there are any new undefined symbols, we need to make
diff --git a/bfd/linker.c b/bfd/linker.c
index 76bc70a..fc52b51 100644
--- a/bfd/linker.c
+++ b/bfd/linker.c
@@ -223,7 +223,10 @@ SUBSUBSECTION
 	archive and decide which elements of the archive should be
 	included in the link.  For each such element it must call the
 	<<add_archive_element>> linker callback, and it must add the
-	symbols from the object file to the linker hash table.
+	symbols from the object file to the linker hash table.  (The
+	callback may in fact indicate that a replacement BFD should be
+	used, in which case the symbols from that BFD should be added
+	to the linker hash table instead.)
 
 @findex _bfd_generic_link_add_archive_symbols
 	In most cases the work of looking through the symbols in the
@@ -243,9 +246,13 @@ SUBSUBSECTION
 	element should be included in the link.  If the element is to
 	be included, the <<add_archive_element>> linker callback
 	routine must be called with the element as an argument, and
-	the elements symbols must be added to the linker hash table
+	the element's symbols must be added to the linker hash table
 	just as though the element had itself been passed to the
-	<<_bfd_link_add_symbols>> function.
+	<<_bfd_link_add_symbols>> function.  The <<add_archive_element>>
+	callback has the option to indicate that it would like to
+	replace the element archive with a substitute BFD, in which
+	case it is the symbols of that substitute BFD that must be
+	added to the linker hash table instead.
 
 	When the a.out <<_bfd_link_add_symbols>> function receives an
 	archive, it calls <<_bfd_generic_link_add_archive_symbols>>
@@ -257,7 +264,8 @@ SUBSUBSECTION
 	symbol) it calls the <<add_archive_element>> callback and then
 	<<aout_link_check_archive_element>> calls
 	<<aout_link_add_symbols>> to actually add the symbols to the
-	linker hash table.
+	linker hash table - possibly those of a substitute BFD, if the
+	<<add_archive_element>> callback avails itself of that option.
 
 	The ECOFF back end is unusual in that it does not normally
 	call <<_bfd_generic_link_add_archive_symbols>>, because ECOFF
@@ -957,8 +965,10 @@ archive_hash_table_init
    included.  CHECKFN should set *PNEEDED to TRUE if the object file
    should be included, and must also call the bfd_link_info
    add_archive_element callback function and handle adding the symbols
-   to the global hash table.  CHECKFN should only return FALSE if some
-   sort of error occurs.
+   to the global hash table.  CHECKFN must notice if the callback
+   indicates a substitute BFD, and arrange to add those symbols instead
+   if it does so.  CHECKFN should only return FALSE if some sort of
+   error occurs.
 
    For some formats, such as a.out, it is possible to look through an
    object file but not actually include it in the link.  The
@@ -1213,11 +1223,20 @@ generic_link_check_archive_element (bfd *abfd,
 	{
 	  bfd_size_type symcount;
 	  asymbol **symbols;
+	  bfd *subsbfd = NULL;
 
 	  /* This object file defines this symbol, so pull it in.  */
-	  if (! (*info->callbacks->add_archive_element) (info, abfd,
-							 bfd_asymbol_name (p)))
+	  if (! (*info->callbacks->add_archive_element)
+				(info, abfd, bfd_asymbol_name (p), &subsbfd))
 	    return FALSE;
+	  /* Potentially, the add_archive_element hook may have set a
+	     substitute BFD for us.  */
+	  if (subsbfd)
+	    {
+	      abfd = subsbfd;
+	      if (!bfd_generic_link_read_symbols (abfd))
+		return FALSE;
+	    }
 	  symcount = _bfd_generic_link_get_symcount (abfd);
 	  symbols = _bfd_generic_link_get_symbols (abfd);
 	  if (! generic_link_add_symbol_list (abfd, info, symcount,
@@ -1238,12 +1257,16 @@ generic_link_check_archive_element (bfd *abfd,
 	  symbfd = h->u.undef.abfd;
 	  if (symbfd == NULL)
 	    {
+	      bfd *subsbfd = NULL;
 	      /* This symbol was created as undefined from outside
 		 BFD.  We assume that we should link in the object
 		 file.  This is for the -u option in the linker.  */
 	      if (! (*info->callbacks->add_archive_element)
-		  (info, abfd, bfd_asymbol_name (p)))
+				(info, abfd, bfd_asymbol_name (p), &subsbfd))
 		return FALSE;
+	      /* Potentially, the add_archive_element hook may have set a
+		 substitute BFD for us.  But no symbols are going to get
+		 registered by anything we're returning to from here.  */
 	      *pneeded = TRUE;
 	      return TRUE;
 	    }
diff --git a/bfd/pdp11.c b/bfd/pdp11.c
index 1a7694c..5f4d28c 100644
--- a/bfd/pdp11.c
+++ b/bfd/pdp11.c
@@ -2545,7 +2545,8 @@ aout_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
 static bfd_boolean
 aout_link_check_ar_symbols (bfd *abfd,
 			    struct bfd_link_info *info,
-			    bfd_boolean *pneeded)
+			    bfd_boolean *pneeded,
+			    bfd **subsbfd)
 {
   struct external_nlist *p;
   struct external_nlist *pend;
@@ -2600,7 +2601,8 @@ aout_link_check_ar_symbols (bfd *abfd,
 	     but not if it is defined in the .text section.  That
 	     seems a bit crazy to me, and I haven't implemented it.
 	     However, it might be correct.  */
-	  if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+	  if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 	    return FALSE;
 	  *pneeded = TRUE;
 	  return TRUE;
@@ -2628,7 +2630,7 @@ aout_link_check_ar_symbols (bfd *abfd,
 			 in the object file.  This is done for the -u
 			 option in the linker.  */
 		      if (! (*info->callbacks->add_archive_element)
-			  (info, abfd, name))
+			  (info, abfd, name, subsbfd))
 			return FALSE;
 		      *pneeded = TRUE;
 		      return TRUE;
@@ -2680,15 +2682,21 @@ aout_link_check_archive_element (bfd *abfd,
 				 struct bfd_link_info *info,
 				 bfd_boolean *pneeded)
 {
+  bfd *subsbfd = NULL;
+
   if (! aout_get_external_symbols (abfd))
     return FALSE;
 
-  if (! aout_link_check_ar_symbols (abfd, info, pneeded))
+  if (! aout_link_check_ar_symbols (abfd, info, pneeded, &subsbfd))
     return FALSE;
 
   if (*pneeded)
     {
-      if (! aout_link_add_symbols (abfd, info))
+      /* Potentially, the add_archive_element hook may have set a
+	 substitute BFD for us.  */
+      if (subsbfd && ! aout_get_external_symbols (subsbfd))
+	return FALSE;
+      if (! aout_link_add_symbols (subsbfd ? subsbfd : abfd, info))
 	return FALSE;
     }
 
diff --git a/bfd/vms-alpha.c b/bfd/vms-alpha.c
index 5d38d1d..ba195f9 100644
--- a/bfd/vms-alpha.c
+++ b/bfd/vms-alpha.c
@@ -8220,6 +8220,7 @@ alpha_vms_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
       symindex symidx;
       bfd *element;
       bfd *orig_element;
+      bfd *subsbfd;
 
       h = *pundef;
       next_pundef = &(*pundef)->u.undef.next;
@@ -8277,10 +8278,14 @@ alpha_vms_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
       /* Unlike the generic linker, we know that this element provides
 	 a definition for an undefined symbol and we know that we want
 	 to include it.  We don't need to check anything.  */
-      if (! (*info->callbacks->add_archive_element) (info, element,
-                                                     h->root.string))
+      subsbfd = NULL;
+      if (! (*info->callbacks->add_archive_element)
+				(info, element, h->root.string, &subsbfd))
 	return FALSE;
-      if (! alpha_vms_link_add_object_symbols (element, info))
+      /* Potentially, the add_archive_element hook may have set a
+	 substitute BFD for us.  */
+      if (! alpha_vms_link_add_object_symbols (subsbfd ? subsbfd : element,
+				info))
 	return FALSE;
 
       orig_element->archive_pass = pass;
diff --git a/bfd/xcofflink.c b/bfd/xcofflink.c
index 30923cf..c055b26 100644
--- a/bfd/xcofflink.c
+++ b/bfd/xcofflink.c
@@ -2233,7 +2233,8 @@ xcoff_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
 static bfd_boolean
 xcoff_link_check_dynamic_ar_symbols (bfd *abfd,
 				     struct bfd_link_info *info,
-				     bfd_boolean *pneeded)
+				     bfd_boolean *pneeded,
+				     bfd **subsbfd)
 {
   asection *lsec;
   bfd_byte *contents;
@@ -2291,7 +2292,8 @@ xcoff_link_check_dynamic_ar_symbols (bfd *abfd,
 	  && (((struct xcoff_link_hash_entry *) h)->flags
 	      & XCOFF_DEF_DYNAMIC) == 0)
 	{
-	  if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+	  if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 	    return FALSE;
 	  *pneeded = TRUE;
 	  return TRUE;
@@ -2314,7 +2316,8 @@ xcoff_link_check_dynamic_ar_symbols (bfd *abfd,
 static bfd_boolean
 xcoff_link_check_ar_symbols (bfd *abfd,
 			     struct bfd_link_info *info,
-			     bfd_boolean *pneeded)
+			     bfd_boolean *pneeded,
+			     bfd **subsbfd)
 {
   bfd_size_type symesz;
   bfd_byte *esym;
@@ -2325,7 +2328,7 @@ xcoff_link_check_ar_symbols (bfd *abfd,
   if ((abfd->flags & DYNAMIC) != 0
       && ! info->static_link
       && info->output_bfd->xvec == abfd->xvec)
-    return xcoff_link_check_dynamic_ar_symbols (abfd, info, pneeded);
+    return xcoff_link_check_dynamic_ar_symbols (abfd, info, pneeded, subsbfd);
 
   symesz = bfd_coff_symesz (abfd);
   esym = (bfd_byte *) obj_coff_external_syms (abfd);
@@ -2361,7 +2364,8 @@ xcoff_link_check_ar_symbols (bfd *abfd,
 		  || (((struct xcoff_link_hash_entry *) h)->flags
 		      & XCOFF_DEF_DYNAMIC) == 0))
 	    {
-	      if (! (*info->callbacks->add_archive_element) (info, abfd, name))
+	      if (! (*info->callbacks->add_archive_element)
+					(info, abfd, name, subsbfd))
 		return FALSE;
 	      *pneeded = TRUE;
 	      return TRUE;
@@ -2386,17 +2390,22 @@ xcoff_link_check_archive_element (bfd *abfd,
 				  bfd_boolean *pneeded)
 {
   bfd_boolean keep_syms_p;
+  bfd *subsbfd = NULL;
 
   keep_syms_p = (obj_coff_external_syms (abfd) != NULL);
   if (! _bfd_coff_get_external_symbols (abfd))
     return FALSE;
 
-  if (! xcoff_link_check_ar_symbols (abfd, info, pneeded))
+  if (! xcoff_link_check_ar_symbols (abfd, info, pneeded, &subsbfd))
     return FALSE;
 
   if (*pneeded)
     {
-      if (! xcoff_link_add_symbols (abfd, info))
+      /* Potentially, the add_archive_element hook may have set a
+	 substitute BFD for us.  */
+      if (subsbfd && !_bfd_coff_get_external_symbols (subsbfd))
+	return FALSE;
+      if (! xcoff_link_add_symbols (subsbfd ? subsbfd : abfd, info))
 	return FALSE;
       if (info->keep_memory)
 	keep_syms_p = TRUE;