pe/coff: handle weak defined symbol for gc-sections.

bfd/
	* coffgen.c (_bfd_coff_gc_mark_hook): Handle PE weak
	external symbols with a definition.
	(_bfd_coff_gc_mark_extra_sections): Fix typo.

ld/
	* testsuite/ld-pe/pe.exp: New test.
	* testsuite/ld-pe/weakdef-1.s: New test source.
	* testsuite/ld-pe/weakdef-1.d: New test.

bfd/ChangeLog

@@ -1,3 +1,9 @@
+2017-04-07  gingold  <gingold@gingold-Precision-7510>
+
+	* coffgen.c (_bfd_coff_gc_mark_hook): Handle PE weak
+	external symbols with a definition.
+	(_bfd_coff_gc_mark_extra_sections): Fix typo.
+
 2017-04-07  Alan Modra  <amodra@gmail.com>
 
 	* po/SRC-POTFILES.in: Regenerate.

bfd/coffgen.c

@@ -2785,8 +2785,22 @@ _bfd_coff_gc_mark_hook (asection *sec,
         case bfd_link_hash_common:
           return h->root.u.c.p->section;
 
-	case bfd_link_hash_undefined:
 	case bfd_link_hash_undefweak:
+	  if (h->symbol_class == C_NT_WEAK && h->numaux == 1)
+	    {
+	      /* PE weak externals.  A weak symbol may include an auxiliary
+		 record indicating that if the weak symbol is not resolved,
+		 another external symbol is used instead.  */
+	      struct coff_link_hash_entry *h2 =
+		h->auxbfd->tdata.coff_obj_data->sym_hashes[
+		    h->aux->x_sym.x_tagndx.l];
+
+	      if (h2 && h2->root.type != bfd_link_hash_undefined)
+		return  h2->root.u.def.section;
+	    }
+	  break;
+
+	case bfd_link_hash_undefined:
         default:
           break;
         }
@@ -2897,7 +2911,7 @@ _bfd_coff_gc_mark_extra_sections (struct bfd_link_info *info,
       asection *isec;
       bfd_boolean some_kept;
 
-      if (bfd_get_flavour (ibfd) != bfd_target_elf_flavour)
+      if (bfd_get_flavour (ibfd) != bfd_target_coff_flavour)
 	continue;
 
       /* Ensure all linker created sections are kept, and see whether

ld/ChangeLog

@@ -1,3 +1,9 @@
+2017-04-07  gingold  <gingold@gingold-Precision-7510>
+
+	* testsuite/ld-pe/pe.exp: New test.
+	* testsuite/ld-pe/weakdef-1.s: New test source.
+	* testsuite/ld-pe/weakdef-1.d: New test.
+
 2017-04-07  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-elf/mbind1a.d: Remove matches for PT_LOAD segments.

ld/testsuite/ld-pe/pe.exp

@@ -76,6 +76,8 @@ run_dump_test "longsecn-5"
 run_dump_test "orphan"
 run_dump_test "orphan_nu"
 
+run_dump_test "weakdef-1"
+
 run_dump_test "pr19803"
 set pr19803_dll {
     {   "PR 19803: not exporting swept symbols"

ld/testsuite/ld-pe/weakdef-1.d

@@ -0,0 +1,8 @@
+#source: weakdef-1.s
+#target: i*86-*-cygwin* i*86-*-pe i*86-*-mingw*
+#ld: -e _start --gc-sections
+#objdump: -d
+
+#...
+  401003:	a1 00 20 40 00       	mov    0x402000,%eax
+#pass

ld/testsuite/ld-pe/weakdef-1.s

@@ -0,0 +1,19 @@
+	.weak	_wsym
+	.section	.data$wsym,"w"
+	.align 4
+_wsym:
+	.long	1
+
+	.section	.text$start,"x"
+	.globl	_start
+	.def	_start;	.scl	2;	.type	32;	.endef
+_start:
+	pushl	%ebp
+	movl	%esp, %ebp
+	movl	_wsym, %eax
+	testl	%eax, %eax
+	sete	%al
+	movzbl	%al, %eax
+	nop
+	popl	%ebp
+	ret