BFD: Prevent writing the MIPS _gp_disp symbol into symbol tables

The _gp_disp is a magic symbol, always implicitly defined by the linker.
It does not make a sense to write it into symbol tables for output files.
Moreover, now if the linker gets a version script, the _gp_disp symbol
gets zero version definition index.  The zero index means[1]:

"The symbol is local, not available outside the object."

But the _gp_disp symbol has GLOBAL binding.  That confuses some tools
like for example the LLD linker when they get such files as inputs.

This patch fixes the problem - it prevents writing the _gp_disp symbol
in regular and dynamic symbol tables.

This was tested by running LD test suite on a mipsel-linux board.

References:

[1] "Linux Standard Base Specification", Section "10.7.2 Symbol
    Version Table", p. 32

2018-05-03  Simon Atanasyan  <simon@atanasyan.com>

bfd/

	* elf32-mips.c: (elf32_mips_fixup_symbol): New function.
	(elf_backend_fixup_symbol): New macro.
	* elfxx-mips.c: (mips_elf_output_extsym): Discard _gp_disp
	handling.
	(_bfd_mips_elf_finish_dynamic_symbol): Likewise.

ld/

	* testsuite/ld-mips-elf/gp-disp-sym.d: New test.
	* testsuite/ld-mips-elf/gp-disp-sym.s: New test source.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new test.
	* testsuite/ld-mips-elf/mips16-pic-2.ad: Update for _gp_disp
	symbol removal.
	* testsuite/ld-mips-elf/mips16-pic-2.nd: Likewise.
	* testsuite/ld-mips-elf/pic-and-nonpic-3a.dd: Likewise.
	* testsuite/ld-mips-elf/tlslib-o32-hidden.got: Likewise.
	* testsuite/ld-mips-elf/tlslib-o32-ver.got: Likewise.
	* testsuite/ld-mips-elf/tlslib-o32.got: Likewise.

3 files changed, 20 insertions, 12 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 11baf5d..94f28b1 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,11 @@
+2018-05-03  Simon Atanasyan  <simon@atanasyan.com>
+
+	* elf32-mips.c: (elf32_mips_fixup_symbol): New function.
+	(elf_backend_fixup_symbol): New macro.
+	* elfxx-mips.c: (mips_elf_output_extsym): Discard _gp_disp
+	handling.
+	(_bfd_mips_elf_finish_dynamic_symbol): Likewise.
+
 2018-04-30  Francois H. Theron <francois.theron@netronome.com>
 
 	* Makefile.am: Added NFP files to build.
diff --git a/bfd/elf32-mips.c b/bfd/elf32-mips.c
index 87147b5..23a5712 100644
--- a/bfd/elf32-mips.c
+++ b/bfd/elf32-mips.c
@@ -2420,6 +2420,17 @@ elf32_mips_write_core_note (bfd *abfd, char *buf, int *bufsiz, int note_type,
       }
     }
 }
+
+/* Remove the magic _gp_disp symbol from the symbol tables.  */
+
+static bfd_boolean
+elf32_mips_fixup_symbol (struct bfd_link_info *info,
+			 struct elf_link_hash_entry *h)
+{
+  if (strcmp (h->root.root.string, "_gp_disp") == 0)
+    _bfd_elf_link_hash_hide_symbol (info, h, TRUE);
+  return TRUE;
+}
 
 /* Depending on the target vector we generate some version of Irix
    executables or "normal" MIPS ELF ABI executables.  */
@@ -2523,6 +2534,7 @@ static const struct ecoff_debug_swap mips_elf32_ecoff_debug_swap = {
 #define elf_backend_gc_mark_hook	_bfd_mips_elf_gc_mark_hook
 #define elf_backend_copy_indirect_symbol \
 					_bfd_mips_elf_copy_indirect_symbol
+#define elf_backend_fixup_symbol	elf32_mips_fixup_symbol
 #define elf_backend_grok_prstatus	elf32_mips_grok_prstatus
 #define elf_backend_grok_psinfo		elf32_mips_grok_psinfo
 #define elf_backend_ecoff_debug_swap	&mips_elf32_ecoff_debug_swap
diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index ce64581..e349e8a 100644
--- a/bfd/elfxx-mips.c
+++ b/bfd/elfxx-mips.c
@@ -2903,12 +2903,6 @@ mips_elf_output_extsym (struct mips_elf_link_hash_entry *h, void *data)
 	      h->esym.asym.value =
 		mips_elf_hash_table (einfo->info)->procedure_count;
 	    }
-	  else if (strcmp (name, "_gp_disp") == 0 && ! NEWABI_P (einfo->abfd))
-	    {
-	      h->esym.asym.sc = scAbs;
-	      h->esym.asym.st = stLabel;
-	      h->esym.asym.value = elf_gp (einfo->abfd);
-	    }
 	  else
 	    h->esym.asym.sc = scUndefined;
 	}
@@ -10976,12 +10970,6 @@ _bfd_mips_elf_finish_dynamic_symbol (bfd *output_bfd,
       sym->st_info = ELF_ST_INFO (STB_GLOBAL, STT_SECTION);
       sym->st_value = 1;
     }
-  else if (strcmp (name, "_gp_disp") == 0 && ! NEWABI_P (output_bfd))
-    {
-      sym->st_shndx = SHN_ABS;
-      sym->st_info = ELF_ST_INFO (STB_GLOBAL, STT_SECTION);
-      sym->st_value = elf_gp (output_bfd);
-    }
   else if (SGI_COMPAT (output_bfd))
     {
       if (strcmp (name, mips_elf_dynsym_rtproc_names[0]) == 0