x86: Remove the unused _GLOBAL_OFFSET_TABLE_

Since _GLOBAL_OFFSET_TABLE_ may be referenced implicitly on x86,
checking ref_regular_nonweak leaves the unused _GLOBAL_OFFSET_TABLE_
in output.  This patch checks explicit GOT references instead.

ld-i386/discarded1.s and ld-x86-64/discarded1.s are updated to avoid
linker optimization which removes GOT references.

bfd/

	PR ld/22782
	* elf32-i386.c (elf_i386_check_relocs): Set got_referenced if
	_GLOBAL_OFFSET_TABLE_ is referenced or GOT is needed to resolve
	undefined weak symbol to 0.
	* elf64-x86-64.c (elf_x86_64_check_relocs): Set got_referenced
	if _GLOBAL_OFFSET_TABLE_ is referenced.
	* elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Check
	got_referenced instead of ref_regular_nonweak.  Remove the
	unused _GLOBAL_OFFSET_TABLE_ from symbol table.
	* elfxx-x86.h (elf_x86_link_hash_table): Add got_referenced.

ld/

	PR ld/22782
	* testsuite/ld-i386/discarded1.s: Replace mov with div.
	* testsuite/ld-x86-64/discarded1.s: Likewise.
	* testsuite/ld-i386/i386.exp: Run pr22782.
	* testsuite/ld-i386/load1-nacl.d: Updated for removing
	_GLOBAL_OFFSET_TABLE_ from output.
	* testsuite/ld-i386/load1.d: Likewise.
	* testsuite/ld-x86-64/load1a-nacl.d: Likewise.
	* testsuite/ld-x86-64/load1a.d: Likewise.
	* testsuite/ld-x86-64/load1b-nacl.d: Likewise.
	* testsuite/ld-x86-64/load1b.d: Likewise.
	* testsuite/ld-i386/pr22782.d: New file.
	* testsuite/ld-i386/pr22782.s: Likewise.
	* testsuite/ld-x86-64/pr22782.s: Likewise.
	* testsuite/ld-x86-64/pr22782a.d: Likewise.
	* testsuite/ld-x86-64/pr22782b.d: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run pr22782a and pr22782b.

5 files changed, 49 insertions, 4 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index ecd1c7b..e9accbd 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,16 @@
+2018-02-05  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/22782
+	* elf32-i386.c (elf_i386_check_relocs): Set got_referenced if
+	_GLOBAL_OFFSET_TABLE_ is referenced or GOT is needed to resolve
+	undefined weak symbol to 0.
+	* elf64-x86-64.c (elf_x86_64_check_relocs): Set got_referenced
+	if _GLOBAL_OFFSET_TABLE_ is referenced.
+	* elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Check
+	got_referenced instead of ref_regular_nonweak.  Remove the
+	unused _GLOBAL_OFFSET_TABLE_ from symbol table.
+	* elfxx-x86.h (elf_x86_link_hash_table): Add got_referenced.
+
 2018-02-05  Maciej W. Rozycki  <macro@mips.com>
 
 	* elfnn-riscv.c (_bfd_riscv_relax_pc): Use `memset' to
diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index 1f380db..1bdf3d4 100644
--- a/bfd/elf32-i386.c
+++ b/bfd/elf32-i386.c
@@ -1578,6 +1578,10 @@ elf_i386_check_relocs (bfd *abfd,
 				     rel, rel_end, h, r_symndx, FALSE))
 	goto error_return;
 
+      /* Check if _GLOBAL_OFFSET_TABLE_ is referenced.  */
+      if (h == htab->elf.hgot)
+	htab->got_referenced = TRUE;
+
       switch (r_type)
 	{
 	case R_386_TLS_LDM:
@@ -1720,11 +1724,19 @@ elf_i386_check_relocs (bfd *abfd,
 
 	case R_386_GOTOFF:
 	case R_386_GOTPC:
-	create_got:
+create_got:
 	  if (r_type != R_386_TLS_IE)
 	    {
 	      if (eh != NULL)
-		eh->zero_undefweak &= 0x2;
+		{
+		  eh->zero_undefweak &= 0x2;
+
+		  /* Need GOT to resolve undefined weak symbol to 0.  */
+		  if (r_type == R_386_GOTOFF
+		      && h->root.type == bfd_link_hash_undefweak
+		      && bfd_link_executable (info))
+		    htab->got_referenced = TRUE;
+		}
 	      break;
 	    }
 	  /* Fall through */
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index ba4f47b..aad9b85 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -1927,6 +1927,10 @@ elf_x86_64_check_relocs (bfd *abfd, struct bfd_link_info *info,
 				       rel, rel_end, h, r_symndx, FALSE))
 	goto error_return;
 
+      /* Check if _GLOBAL_OFFSET_TABLE_ is referenced.  */
+      if (h == htab->elf.hgot)
+	htab->got_referenced = TRUE;
+
       eh = (struct elf_x86_link_hash_entry *) h;
       switch (r_type)
 	{
diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index a7db5d9..dbda542 100644
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -1086,7 +1086,7 @@ _bfd_x86_elf_size_dynamic_sections (bfd *output_bfd,
       /* Don't allocate .got.plt section if there are no GOT nor PLT
 	 entries and there is no reference to _GLOBAL_OFFSET_TABLE_.  */
       if ((htab->elf.hgot == NULL
-	   || !htab->elf.hgot->ref_regular_nonweak)
+	   || !htab->got_referenced)
 	  && (htab->elf.sgotplt->size == bed->got_header_size)
 	  && (htab->elf.splt == NULL
 	      || htab->elf.splt->size == 0)
@@ -1096,7 +1096,20 @@ _bfd_x86_elf_size_dynamic_sections (bfd *output_bfd,
 	      || htab->elf.iplt->size == 0)
 	  && (htab->elf.igotplt == NULL
 	      || htab->elf.igotplt->size == 0))
-	htab->elf.sgotplt->size = 0;
+	{
+	  htab->elf.sgotplt->size = 0;
+	  if (htab->elf.hgot != NULL)
+	    {
+	      /* Remove the unused _GLOBAL_OFFSET_TABLE_ from symbol
+		 table. */
+	      htab->elf.hgot->root.type = bfd_link_hash_undefined;
+	      htab->elf.hgot->root.u.undef.abfd
+		= htab->elf.hgot->root.u.def.section->owner;
+	      htab->elf.hgot->root.linker_def = 0;
+	      htab->elf.hgot->ref_regular = 0;
+	      htab->elf.hgot->def_regular = 0;
+	    }
+	}
     }
 
   if (_bfd_elf_eh_frame_present (info))
diff --git a/bfd/elfxx-x86.h b/bfd/elfxx-x86.h
index e2a83ad..b515ee6 100644
--- a/bfd/elfxx-x86.h
+++ b/bfd/elfxx-x86.h
@@ -478,6 +478,9 @@ struct elf_x86_link_hash_table
       is only used for i386.  */
   bfd_byte plt0_pad_byte;
 
+  /* TRUE if GOT is referenced.  */
+  unsigned int got_referenced : 1;
+
   bfd_vma (*r_info) (bfd_vma, bfd_vma);
   bfd_vma (*r_sym) (bfd_vma);
   bfd_boolean (*is_reloc_section) (const char *);