PR22471, undefined reference to linker-defined symbols

This patch processes linker script assignment statements before ld
opens DT_NEEDED libraries, in order to define symbols like __bss_start
that might also be defined by a library, falsely triggering an error
about "DSO missing from command line".

The initial value won't be correct when assigning a symbol from dot,
and I make no attempt to handle all expressions.  For example, an
assignment like "_start_foo = ADDR (.foo)" isn't valid until sections
are laid out, so won't define _start_foo early.  What's here should be
enough for most common scripts, and hopefully won't perturb fragile
scripts.

bfd/
	PR 22471
	* elflink.c (_bfd_elf_merge_symbol): Allow weak symbols to override
	early passes over linker script symbols.
	* linker.c (_bfd_generic_link_add_one_symbol): Allow symbols to
	override early passes over linker script symbols.  Clear ldscript_def
	on symbol definitions.
ld/
	PR 22471
	* ldexp.c (struct definedness_hash_entry): Delete "by_script".  Make
	"iteration" an 8-bit field, and update mask in all uses.
	(definedness_newfunc): Don't init "by_script".
	(update_definedness): Test ldscript_def rather than by_script.
	(is_sym_value): Likewise.
	(fold_name <DEFINED>): Return a result for first phase.  Test
	ldscript_def.
	(fold_name <NAME>): Return a result for first phase.
	* ldlang.c (open_input_bfds): Process all assignments, not just
	defsym.
	(lang_process): Increment lang_statement_iteration before
	open_input_bfds.
	* testsuite/ld-mips-elf/tlsdyn-o32-1.d: Adjust for larger .dynsym.
	* testsuite/ld-mips-elf/tlsdyn-o32-1.got: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-2.d: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-2.got: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-3.d: Likewise.
	* testsuite/ld-mips-elf/tlsdyn-o32-3.got: Likewise.

3 files changed, 23 insertions, 2 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index dc3aa2f..c9c2407 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,5 +1,14 @@
 2017-11-28  Alan Modra  <amodra@gmail.com>
 
+	PR 22471
+	* elflink.c (_bfd_elf_merge_symbol): Allow weak symbols to override
+	early passes over linker script symbols.
+	* linker.c (_bfd_generic_link_add_one_symbol): Allow symbols to
+	override early passes over linker script symbols.  Clear ldscript_def
+	on symbol definitions.
+
+2017-11-28  Alan Modra  <amodra@gmail.com>
+
 	* elf64-mmix.c (bfd_elf64_bfd_copy_link_hash_symbol_type): Define.
 
 2017-11-28  H.J. Lu  <hongjiu.lu@intel.com>
diff --git a/bfd/elflink.c b/bfd/elflink.c
index ddd088c..fed7caa 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -1471,10 +1471,15 @@ _bfd_elf_merge_symbol (bfd *abfd,
      treated as strong if the new symbol is from a dynamic library.
      This reflects the way glibc's ld.so works.
 
+     Also allow a weak symbol to override a linker script symbol
+     defined by an early pass over the script.  This is done so the
+     linker knows the symbol is defined in an object file, for the
+     DEFINED script function.
+
      Do this before setting *type_change_ok or *size_change_ok so that
      we warn properly when dynamic library symbols are overridden.  */
 
-  if (newdef && !newdyn && olddyn)
+  if (newdef && !newdyn && (olddyn || h->root.ldscript_def))
     newweak = FALSE;
   if (olddef && newdyn)
     oldweak = FALSE;
diff --git a/bfd/linker.c b/bfd/linker.c
index a96c6ed..9c19df4 100644
--- a/bfd/linker.c
+++ b/bfd/linker.c
@@ -1443,9 +1443,14 @@ _bfd_generic_link_add_one_symbol (struct bfd_link_info *info,
   do
     {
       enum link_action action;
+      int prev;
 
+      prev = h->type;
+      /* Treat symbols defined by early linker script pass as undefined.  */
+      if (h->ldscript_def)
+	prev = bfd_link_hash_undefined;
       cycle = FALSE;
-      action = link_action[(int) row][(int) h->type];
+      action = link_action[(int) row][prev];
       switch (action)
 	{
 	case FAIL:
@@ -1489,6 +1494,7 @@ _bfd_generic_link_add_one_symbol (struct bfd_link_info *info,
 	    h->u.def.section = section;
 	    h->u.def.value = value;
 	    h->linker_def = 0;
+	    h->ldscript_def = 0;
 
 	    /* If we have been asked to, we act like collect2 and
 	       identify all functions that might be global
@@ -1588,6 +1594,7 @@ _bfd_generic_link_add_one_symbol (struct bfd_link_info *info,
 	  else
 	    h->u.c.p->section = section;
 	  h->linker_def = 0;
+	  h->ldscript_def = 0;
 	  break;
 
 	case REF: