PR ld/20828: Fix linker script symbols wrongly forced local with section GC

Fix a generic ELF linker regression introduced with a chain of changes
made to unused input section garbage collection:

- commit 1a766c6843ce ("Also hide symbols without PLT nor GOT
  references."),
  <https://sourceware.org/ml/binutils/2011-09/msg00076.html>,

- commit 1d5316ab67e1 ("PR ld/13177: garbage collector retains zombie
  references to external libraries"),
  <https://sourceware.org/ml/binutils/2011-10/msg00161.html>,

- commit 6673f753c019 ("Fix PR 12772, garbage collection of dynamic
  syms"), <https://sourceware.org/ml/binutils/2011-12/msg00077.html>,

causing the garbage collection of unused symbols present in a DSO
involved in a link to make identically named symbols ordinarily defined
(i.e. not hidden or PROVIDEd) by a linker script local, even though the
latter symbols are supposed to be global as if no DSO defined them as
well.

This is because linker script assignments are processed very late as
`lang_process' proceeds, down in the call to `ldemul_before_allocation',
which is made after the call to `lang_gc_sections' to do input section
garbage collecting.  Consequently if unused, then any such DSO-defined
symbol has already been garbage-collected and internally marked local.
It would ordinarily be removed from dynamic symbol table output, however
a linker script assignment correctly replaces its original definition
with the new one and enters it into the dynamic symbol table produced as
it is supposed to be exported.  The original local marking is however
retained making the symbol local in the dynamic symbol table and
therefore not available externally.  This also causes a sorting problem
with the MIPS target, which does not expect non-section local dynamic
symbols to be output and produces an invalid binary.

Fix the problem then, by removing the `forced_local' marking for the
offending case and add suitable test cases.  First to verify that unused
symbols ordinarily defined with linker script assignments remain
exported in the context of input section garbage collection whether or
not a DSO defining identically named symbols is present in the link.
Second that a linker version script still correctly retains or removes
such symbols as requested.

	bfd/
	PR ld/20828
	* elflink.c (bfd_elf_record_link_assignment): Clear any
	`forced_local' marking for DSO symbols that are not being
	provided.

	ld/
	PR ld/20828
	* testsuite/ld-elf/pr20828-1.sd: New test.
	* testsuite/ld-elf/pr20828-2a.sd: New test.
	* testsuite/ld-elf/pr20828-2b.sd: New test.
	* testsuite/ld-elf/pr20828.ld: New test linker script.
	* testsuite/ld-elf/pr20828.ver: New test version script.
	* testsuite/ld-elf/pr20828.s: New test source.
	* testsuite/ld-elf/shared.exp: Run the new test.

(cherry picked from commit 81ff47b3a54633819fac4d973e34f1ff0c65606e)

8 files changed, 108 insertions, 0 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index 080697e..da85561 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,5 +1,16 @@
 2017-01-18  Maciej W. Rozycki  <macro@imgtec.com>
 
+	PR ld/20828
+	* testsuite/ld-elf/pr20828-1.sd: New test.
+	* testsuite/ld-elf/pr20828-2a.sd: New test.
+	* testsuite/ld-elf/pr20828-2b.sd: New test.
+	* testsuite/ld-elf/pr20828.ld: New test linker script.
+	* testsuite/ld-elf/pr20828.ver: New test version script.
+	* testsuite/ld-elf/pr20828.s: New test source.
+	* testsuite/ld-elf/shared.exp: Run the new test.
+
+2017-01-18  Maciej W. Rozycki  <macro@imgtec.com>
+
 	PR gas/20649
 	* testsuite/ld-mips-elf/mips-elf.exp: Add PIC comdat GOT16/LO16
 	relocation pairing link test.
diff --git a/ld/testsuite/ld-elf/pr20828-1.sd b/ld/testsuite/ld-elf/pr20828-1.sd
new file mode 100644
index 0000000..c47eb1d
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr20828-1.sd
@@ -0,0 +1,12 @@
+# Make sure symbols are global rather than local in the dynamic symbol table,
+# e.g.:
+#    Num:    Value  Size Type    Bind   Vis      Ndx Name
+#      1: 00000000     0 NOTYPE  GLOBAL DEFAULT    1 _fdata
+#      2: 00000000     0 NOTYPE  GLOBAL DEFAULT    1 _edata
+# vs:
+#      1: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 _fdata
+#      2: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 _edata
+#...
+ *[0-9]+: +[0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_fdata
+ *[0-9]+: +[0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_edata
+#pass
diff --git a/ld/testsuite/ld-elf/pr20828-2a.sd b/ld/testsuite/ld-elf/pr20828-2a.sd
new file mode 100644
index 0000000..c4b239b
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr20828-2a.sd
@@ -0,0 +1,9 @@
+# Make sure `_edata' is global rather than local in the dynamic symbol table,
+# e.g.:
+#    Num:    Value  Size Type    Bind   Vis      Ndx Name
+#      1: 00000000     0 NOTYPE  GLOBAL DEFAULT    1 _edata
+# vs:
+#      1: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 _edata
+#...
+ *[0-9]+: +[0-9a-f]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_edata
+#pass
diff --git a/ld/testsuite/ld-elf/pr20828-2b.sd b/ld/testsuite/ld-elf/pr20828-2b.sd
new file mode 100644
index 0000000..8089c48
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr20828-2b.sd
@@ -0,0 +1,7 @@
+# Make sure no `_fdata' is present in the dynamic symbol table, e.g.:
+#    Num:    Value  Size Type    Bind   Vis      Ndx Name
+#      1: 00000000     0 NOTYPE  LOCAL  DEFAULT    1 _fdata
+#failif
+#...
+.+ +_fdata
+#pass
diff --git a/ld/testsuite/ld-elf/pr20828.ld b/ld/testsuite/ld-elf/pr20828.ld
new file mode 100644
index 0000000..9ca1943
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr20828.ld
@@ -0,0 +1,19 @@
+SECTIONS
+{
+  .data :
+  {
+    _fdata = .;
+    *(.data)
+    _edata = .;
+  }
+  .dynamic : { *(.dynamic) }
+  .hash : { *(.hash) }
+  .dynsym : { *(.dynsym) }
+  .dynstr : { *(.dynstr) }
+  .shstrtab : { *(.shstrtab) }
+  .symtab : { *(.symtab) }
+  .strtab : { *(.strtab) }
+  .got.plt : { *(.got.plt) }
+  .got : { *(.got) }
+  /DISCARD/ : { *(*) }
+}
diff --git a/ld/testsuite/ld-elf/pr20828.s b/ld/testsuite/ld-elf/pr20828.s
new file mode 100644
index 0000000..ece49d5
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr20828.s
@@ -0,0 +1,2 @@
+	.data
+	.byte	0
diff --git a/ld/testsuite/ld-elf/pr20828.ver b/ld/testsuite/ld-elf/pr20828.ver
new file mode 100644
index 0000000..7d0fa22
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr20828.ver
@@ -0,0 +1 @@
+{ global: _edata; local: *; };
diff --git a/ld/testsuite/ld-elf/shared.exp b/ld/testsuite/ld-elf/shared.exp
index 3cdac45..dfbf438 100644
--- a/ld/testsuite/ld-elf/shared.exp
+++ b/ld/testsuite/ld-elf/shared.exp
@@ -32,6 +32,53 @@ if ![is_elf_format] {
     return
 }
 
+# This target requires extra GAS options when building code for shared
+# libraries.
+set AFLAGS_PIC ""
+if [istarget "tic6x-*-*"] {
+    append AFLAGS_PIC " -mpic -mpid=near"
+}
+# This target requires a non-default emulation for successful shared
+# library/executable builds.
+set LFLAGS ""
+if [istarget "tic6x-*-*"] {
+    append LFLAGS " -melf32_tic6x_le"
+}
+
+# PR ld/20828 check for correct dynamic symbol table entries where:
+# - symbols have been defined with a linker script,
+# - the same symbols have been seen in shared library used in the link,
+# - the shared library symbols have been swept in section garbage collection.
+# Verify that the symbols are global rather than local and that a version
+# script adjusts them accordingly.
+if { [check_gc_sections_available] } {
+    run_ld_link_tests [list \
+	[list \
+	    "PR ld/20828 dynamic symbols with section GC\
+	      (auxiliary shared library)" \
+	     "$LFLAGS -shared --gc-sections -T pr20828.ld" "" "$AFLAGS_PIC" \
+	     {pr20828.s} \
+	     {{readelf --dyn-syms pr20828-1.sd}} \
+	     "libpr20828.so"] \
+	[list \
+	    "PR ld/20828 dynamic symbols with section GC (plain)" \
+	     "$LFLAGS -shared --gc-sections -T pr20828.ld" \
+	     "tmpdir/libpr20828.so" "$AFLAGS_PIC" \
+	     {pr20828.s} \
+	     {{readelf --dyn-syms pr20828-1.sd}} \
+	     "pr20828-1.so"] \
+	[list \
+	    "PR ld/20828 dynamic symbols with section GC (version script)" \
+	     "$LFLAGS -shared --gc-sections -T pr20828.ld\
+	      --version-script=pr20828.ver" \
+	     "tmpdir/libpr20828.so" \
+	     "$AFLAGS_PIC" \
+	     {pr20828.s} \
+	     {{readelf --dyn-syms pr20828-2a.sd} \
+	      {readelf --dyn-syms pr20828-2b.sd}} \
+	     "pr20828-2.so"]]
+}
+
 # Check to see if the C compiler works
 if { [which $CC] == 0 } {
     return