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[PATCH] BFD: Prevent writing the MIPS _gp_disp symbol into symbol tables

From: Simon Atanasyan <simon at atanasyan dot com>
To: binutils at sourceware dot org
Date: Sun, 28 Jan 2018 13:29:23 +0300
Subject: [PATCH] BFD: Prevent writing the MIPS _gp_disp symbol into symbol tables
Authentication-results: sourceware.org; auth=none
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. This symbol is global while the zero
index means unversioned local symbol. That confuses some tools like for
example the LLD linker when they get such files as inputs.

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

2018-01-25  Simon Atanasyan  <simon.atanasyan@mips.com>

bfd/

	* elf32-mips.c: (elf32_mips_fixup_symbol ): New function.
	(elf_backend_fixup_symbol): New macro.
	* elfxx-mips.c: (_bfd_mips_elf_link_output_symbol_hook): Discard
	the _gp_disp symbol in case of O32 ABI.

testsuite/ld

	* ld-mips-elf/mips16-pic-2.ad: Update test case expectations.
	* ld-mips-elf/mips16-pic-2.nd: Likewise.
	* ld-mips-elf/pic-and-nonpic-3a.dd: Likewise.
	* ld-mips-elf/tlslib-o32-hidden.got: Likewise.
	* ld-mips-elf/tlslib-o32-ver.got: Likewise.
	* ld-mips-elf/tlslib-o32.got: Likewise.

diff --git a/bfd/elf32-mips.c b/bfd/elf32-mips.c
index fa0cc15aba..5f5b08136f 100644
--- a/bfd/elf32-mips.c
+++ b/bfd/elf32-mips.c
@@ -2414,6 +2414,22 @@ elf32_mips_write_core_note (bfd *abfd, char *buf, int *bufsiz, int note_type,
       }
     }
 }
+
+/* Remove magic _gp_disp symbol from the dynamic symbol table.  */
+
+static bfd_boolean
+elf32_mips_fixup_symbol (struct bfd_link_info *info,
+			    struct elf_link_hash_entry *h)
+{
+  const char *name = h->root.root.string;
+  if (h->dynindx != -1 && strcmp(name, "_gp_disp") == 0)
+    {
+      h->dynindx = -1;
+      _bfd_elf_strtab_delref (elf_hash_table (info)->dynstr,
+			      h->dynstr_index);
+    }
+  return TRUE;
+}
 
 /* Depending on the target vector we generate some version of Irix
    executables or "normal" MIPS ELF ABI executables.  */
@@ -2598,6 +2614,9 @@ static const struct ecoff_debug_swap mips_elf32_ecoff_debug_swap = {
 #undef elf_backend_write_core_note
 #define elf_backend_write_core_note	elf32_mips_write_core_note
 
+#undef elf_backend_fixup_symbol
+#define elf_backend_fixup_symbol elf32_mips_fixup_symbol
+
 /* Include the target file again for this target.  */
 #include "elf32-target.h"
 
@@ -2620,6 +2639,7 @@ static const struct ecoff_debug_swap mips_elf32_ecoff_debug_swap = {
 #define elf32_bed				elf32_fbsd_tradbed
 
 #undef elf_backend_write_core_note
+#undef elf_backend_fixup_symbol
 
 #include "elf32-target.h"
 /* Implement elf_backend_final_write_processing for VxWorks.  */
diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index 285401367d..f387ca47db 100644
--- a/bfd/elfxx-mips.c
+++ b/bfd/elfxx-mips.c
@@ -7741,9 +7741,16 @@ _bfd_mips_elf_add_symbol_hook (bfd *abfd, struct bfd_link_info *info,
 int
 _bfd_mips_elf_link_output_symbol_hook
   (struct bfd_link_info *info ATTRIBUTE_UNUSED,
-   const char *name ATTRIBUTE_UNUSED, Elf_Internal_Sym *sym,
-   asection *input_sec, struct elf_link_hash_entry *h ATTRIBUTE_UNUSED)
+   const char *name, Elf_Internal_Sym *sym, asection *input_sec,
+   struct elf_link_hash_entry *h ATTRIBUTE_UNUSED)
 {
+  /* Discard the _gp_disp symbol.  */
+  if (! NEWABI_P (info->output_bfd)
+      && ! bfd_link_relocatable (info)
+      && name
+      && strcmp (name, "_gp_disp") == 0)
+    return 2;
+
   /* If we see a common symbol, which implies a relocatable link, then
      if a symbol was small common in an input file, mark it as small
      common in the output file.  */
diff --git a/ld/testsuite/ld-mips-elf/mips16-pic-2.ad b/ld/testsuite/ld-mips-elf/mips16-pic-2.ad
index 52d3ea4c3b..689f0c2557 100644
--- a/ld/testsuite/ld-mips-elf/mips16-pic-2.ad
+++ b/ld/testsuite/ld-mips-elf/mips16-pic-2.ad
@@ -1,6 +1,6 @@
 # [MIPS_GOTSYM, MIPS_SYMTABNO) covers used4...used7.
 #...
- .* \(MIPS_SYMTABNO\) * 8
+ .* \(MIPS_SYMTABNO\) * 7
 #...
- .* \(MIPS_GOTSYM\) * 0x4
+ .* \(MIPS_GOTSYM\) * 0x3
 #pass
diff --git a/ld/testsuite/ld-mips-elf/mips16-pic-2.nd b/ld/testsuite/ld-mips-elf/mips16-pic-2.nd
index bc2cd38ee9..a2a579412f 100644
--- a/ld/testsuite/ld-mips-elf/mips16-pic-2.nd
+++ b/ld/testsuite/ld-mips-elf/mips16-pic-2.nd
@@ -1,9 +1,9 @@
 # used8 should come before MIPS_GOTSYM.
 #...
- +3: 000405bc +36 +FUNC +GLOBAL +DEFAULT .* used8
- +4: 00040574 +36 +FUNC +GLOBAL +DEFAULT .* used6
- +5: 00040598 +36 +FUNC +GLOBAL +DEFAULT .* used7
- +6: 00040550 +36 +FUNC +GLOBAL +DEFAULT .* used5
- +7: 0004052c +36 +FUNC +GLOBAL +DEFAULT .* used4
+ +2: 000405bc +36 +FUNC +GLOBAL +DEFAULT .* used8
+ +3: 00040574 +36 +FUNC +GLOBAL +DEFAULT .* used6
+ +4: 00040598 +36 +FUNC +GLOBAL +DEFAULT .* used7
+ +5: 00040550 +36 +FUNC +GLOBAL +DEFAULT .* used5
+ +6: 0004052c +36 +FUNC +GLOBAL +DEFAULT .* used4
 
 #pass
diff --git a/ld/testsuite/ld-mips-elf/pic-and-nonpic-3a.dd b/ld/testsuite/ld-mips-elf/pic-and-nonpic-3a.dd
index 3dcfe12cfc..b286f131f4 100644
--- a/ld/testsuite/ld-mips-elf/pic-and-nonpic-3a.dd
+++ b/ld/testsuite/ld-mips-elf/pic-and-nonpic-3a.dd
@@ -35,5 +35,5 @@ Disassembly of section \.MIPS\.stubs:
  c00:	8f998010 	lw	t9,-32752\(gp\)
  c04:	03e07825 	move	t7,ra
  c08:	0320f809 	jalr	t9
- c0c:	24180005 	li	t8,5
+ c0c:	24180004 	li	t8,4
 	\.\.\.
diff --git a/ld/testsuite/ld-mips-elf/tlslib-o32-hidden.got b/ld/testsuite/ld-mips-elf/tlslib-o32-hidden.got
index 563d8bb082..a746031f7e 100644
--- a/ld/testsuite/ld-mips-elf/tlslib-o32-hidden.got
+++ b/ld/testsuite/ld-mips-elf/tlslib-o32-hidden.got
@@ -4,11 +4,11 @@
 DYNAMIC RELOCATION RECORDS
 OFFSET   TYPE              VALUE 
 00000000 R_MIPS_NONE       \*ABS\*
-000403bc R_MIPS_TLS_TPREL32  \*ABS\*
-000403c0 R_MIPS_TLS_DTPMOD32  \*ABS\*
-000403c8 R_MIPS_TLS_DTPMOD32  \*ABS\*
+0004039c R_MIPS_TLS_TPREL32  \*ABS\*
+000403a0 R_MIPS_TLS_DTPMOD32  \*ABS\*
+000403a8 R_MIPS_TLS_DTPMOD32  \*ABS\*
 
 
 Contents of section .got:
- 403b0 00000000 80000000 00000380 00000008  ................
- 403c0 00000000 ffff8004 00000000 00000000  ................
+ 40390 00000000 80000000 00000360 00000008  ................
+ 403a0 00000000 ffff8004 00000000 00000000  ................
diff --git a/ld/testsuite/ld-mips-elf/tlslib-o32-ver.got b/ld/testsuite/ld-mips-elf/tlslib-o32-ver.got
index e675f9f64a..17a6385e8e 100644
--- a/ld/testsuite/ld-mips-elf/tlslib-o32-ver.got
+++ b/ld/testsuite/ld-mips-elf/tlslib-o32-ver.got
@@ -4,12 +4,12 @@
 DYNAMIC RELOCATION RECORDS
 OFFSET   TYPE              VALUE 
 00000000 R_MIPS_NONE       \*ABS\*
-000404d8 R_MIPS_TLS_DTPMOD32  \*ABS\*
-000404d0 R_MIPS_TLS_DTPMOD32  tlsvar_gd@@VER_1
-000404d4 R_MIPS_TLS_DTPREL32  tlsvar_gd@@VER_1
-000404cc R_MIPS_TLS_TPREL32  tlsvar_ie@@VER_1
+000404b8 R_MIPS_TLS_DTPMOD32  \*ABS\*
+000404b0 R_MIPS_TLS_DTPMOD32  tlsvar_gd@@VER_1
+000404b4 R_MIPS_TLS_DTPREL32  tlsvar_gd@@VER_1
+000404ac R_MIPS_TLS_TPREL32  tlsvar_ie@@VER_1
 
 
 Contents of section .got:
- 404c0 00000000 80000000 00000490 00000000  ................
- 404d0 00000000 00000000 00000000 00000000  ................
+ 404a0 00000000 80000000 00000470 00000000  ................
+ 404b0 00000000 00000000 00000000 00000000  ................
diff --git a/ld/testsuite/ld-mips-elf/tlslib-o32.got b/ld/testsuite/ld-mips-elf/tlslib-o32.got
index ad90fb019e..a389c30146 100644
--- a/ld/testsuite/ld-mips-elf/tlslib-o32.got
+++ b/ld/testsuite/ld-mips-elf/tlslib-o32.got
@@ -4,12 +4,12 @@ tmpdir/tlslib-o32.so:     file format elf32-tradbigmips
 DYNAMIC RELOCATION RECORDS
 OFFSET   TYPE              VALUE 
 00000000 R_MIPS_NONE       \*ABS\*
-00040448 R_MIPS_TLS_DTPMOD32  \*ABS\*
-00040440 R_MIPS_TLS_DTPMOD32  tlsvar_gd
-00040444 R_MIPS_TLS_DTPREL32  tlsvar_gd
-0004043c R_MIPS_TLS_TPREL32  tlsvar_ie
+00040428 R_MIPS_TLS_DTPMOD32  \*ABS\*
+00040420 R_MIPS_TLS_DTPMOD32  tlsvar_gd
+00040424 R_MIPS_TLS_DTPREL32  tlsvar_gd
+0004041c R_MIPS_TLS_TPREL32  tlsvar_ie
 
 
 Contents of section .got:
- 40430 00000000 80000000 00000400 00000000  ................
- 40440 00000000 00000000 00000000 00000000  ................
+ 40410 00000000 80000000 000003e0 00000000  ................
+ 40420 00000000 00000000 00000000 00000000  ................
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