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.

10 files changed, 56 insertions, 25 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index d11cd06..55daa0d 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,16 @@
+2018-05-03  Simon Atanasyan  <simon@atanasyan.com>
+
+	* 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.
+
 2018-04-27  Maciej W. Rozycki  <macro@mips.com>
 
 	* testsuite/ld-mips-elf/bal-jalx-pic.d: Only run for
diff --git a/ld/testsuite/ld-mips-elf/gp-disp-sym.d b/ld/testsuite/ld-mips-elf/gp-disp-sym.d
new file mode 100644
index 0000000..00f19cc
--- /dev/null
+++ b/ld/testsuite/ld-mips-elf/gp-disp-sym.d
@@ -0,0 +1,9 @@
+#name: MIPS _gp_disp removal from symbol tables
+#ld: -shared
+#objdump: -tT
+#target: [check_shared_lib_support]
+
+#failif
+#...
+.*_gp_disp
+#pass
diff --git a/ld/testsuite/ld-mips-elf/gp-disp-sym.s b/ld/testsuite/ld-mips-elf/gp-disp-sym.s
new file mode 100644
index 0000000..c6380ba
--- /dev/null
+++ b/ld/testsuite/ld-mips-elf/gp-disp-sym.s
@@ -0,0 +1,5 @@
+  .global foo
+  .text
+foo:
+  lui    $t0, %hi(_gp_disp)
+  addi   $t0, $t0, %lo(_gp_disp)
diff --git a/ld/testsuite/ld-mips-elf/mips-elf.exp b/ld/testsuite/ld-mips-elf/mips-elf.exp
index 95d677e..6668e22 100644
--- a/ld/testsuite/ld-mips-elf/mips-elf.exp
+++ b/ld/testsuite/ld-mips-elf/mips-elf.exp
@@ -1255,3 +1255,7 @@ run_dump_test "mips-abiflags-1"
 run_dump_test "mips-abiflags-1r"
 run_dump_test "mips-abiflags-2"
 run_dump_test "mips-abiflags-2r"
+
+# Test that _gp_disp symbol is not present in symbol tables.
+run_dump_test "gp-disp-sym" [list [list as $abi_asflags(o32)] \
+				  [list ld $abi_ldflags(o32)]]
diff --git a/ld/testsuite/ld-mips-elf/mips16-pic-2.ad b/ld/testsuite/ld-mips-elf/mips16-pic-2.ad
index 52d3ea4..689f0c2 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 bc2cd38..a2a5794 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 3dcfe12..b286f13 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 563d8bb..a746031 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 e675f9f..17a6385 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 ad90fb0..a389c30 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  ................