Strip global symbol defined in discarded section

When a global symbol is defined in COMDAT group, we shouldn't leave an
undefined symbol in symbol table when the symbol section is discarded
unless there is a reference to the symbol outside of COMDAT group.

bfd/

	PR ld/17550
	* elf-bfd.h (elf_link_hash_entry): Update comments for indx,
	documenting that indx == -3 if symbol is defined in a discarded
	section.
	* elflink.c (elf_link_add_object_symbols): Set indx to -3 if
	symbol is defined in a discarded section.
	(elf_link_output_extsym): Strip a global symbol defined in a
	discarded section.

ld/

	PR ld/17550
	* testsuite/ld-elf/pr17550-1.s: New file.
	* testsuite/ld-elf/pr17550-2.s: Likewise.
	* testsuite/ld-elf/pr17550-3.s: Likewise.
	* testsuite/ld-elf/pr17550-4.s: Likewise.
	* testsuite/ld-elf/pr17550a.d: Likewise.
	* testsuite/ld-elf/pr17550b.d: Likewise.
	* testsuite/ld-elf/pr17550c.d: Likewise.
	* testsuite/ld-elf/pr17550d.d: Likewise.

12 files changed, 131 insertions, 1 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index c6a51c4..dfd9c1b 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,5 +1,16 @@
 2016-05-06  H.J. Lu  <hongjiu.lu@intel.com>
 
+	PR ld/17550
+	* elf-bfd.h (elf_link_hash_entry): Update comments for indx,
+	documenting that indx == -3 if symbol is defined in a discarded
+	section.
+	* elflink.c (elf_link_add_object_symbols): Set indx to -3 if
+	symbol is defined in a discarded section.
+	(elf_link_output_extsym): Strip a global symbol defined in a
+	discarded section.
+
+2016-05-06  H.J. Lu  <hongjiu.lu@intel.com>
+
 	* elf32-i386.c (elf_backend_add_symbol_hook): Defined for Intel
 	MCU.
 
diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 9067dd9..863fc39 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -124,7 +124,8 @@ struct elf_link_hash_entry
   struct bfd_link_hash_entry root;
 
   /* Symbol index in output file.  This is initialized to -1.  It is
-     set to -2 if the symbol is used by a reloc.  */
+     set to -2 if the symbol is used by a reloc.  It is set to -3 if
+     this symbol is defined in a discarded section.  */
   long indx;
 
   /* Symbol index as a dynamic symbol.  Initialized to -1, and remains
diff --git a/bfd/elflink.c b/bfd/elflink.c
index b6ff6b6..6ccd5fc 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -4082,6 +4082,7 @@ error_free_dyn:
       bfd_boolean old_weak;
       bfd_boolean override;
       bfd_boolean common;
+      bfd_boolean discarded;
       unsigned int old_alignment;
       bfd *old_bfd;
       bfd_boolean matched;
@@ -4092,6 +4093,7 @@ error_free_dyn:
       sec = NULL;
       value = isym->st_value;
       common = bed->common_definition (isym);
+      discarded = FALSE;
 
       bind = ELF_ST_BIND (isym->st_info);
       switch (bind)
@@ -4142,6 +4144,7 @@ error_free_dyn:
 	      /* Symbols from discarded section are undefined.  We keep
 		 its visibility.  */
 	      sec = bfd_und_section_ptr;
+	      discarded = TRUE;
 	      isym->st_shndx = SHN_UNDEF;
 	    }
 	  else if ((abfd->flags & (EXEC_P | DYNAMIC)) != 0)
@@ -4385,6 +4388,11 @@ error_free_dyn:
 	     || h->root.type == bfd_link_hash_warning)
 	h = (struct elf_link_hash_entry *) h->root.u.i.link;
 
+      /* Setting the index to -3 tells elf_link_output_extsym that
+	 this symbol is defined in a discarded section.  */
+      if (discarded)
+	h->indx = -3;
+
       *sym_hash = h;
 
       new_weak = (flags & BSF_WEAK) != 0;
@@ -9201,6 +9209,10 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data)
 	      return FALSE;
 	    }
 	}
+
+      /* Strip a global symbol defined in a discarded section.  */
+      if (h->indx == -3)
+	return TRUE;
     }
 
   /* We should also warn if a forced local symbol is referenced from
diff --git a/ld/ChangeLog b/ld/ChangeLog
index ecb9cd9..97031bd 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,15 @@
+2016-05-06  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/17550
+	* testsuite/ld-elf/pr17550-1.s: New file.
+	* testsuite/ld-elf/pr17550-2.s: Likewise.
+	* testsuite/ld-elf/pr17550-3.s: Likewise.
+	* testsuite/ld-elf/pr17550-4.s: Likewise.
+	* testsuite/ld-elf/pr17550a.d: Likewise.
+	* testsuite/ld-elf/pr17550b.d: Likewise.
+	* testsuite/ld-elf/pr17550c.d: Likewise.
+	* testsuite/ld-elf/pr17550d.d: Likewise.
+
 2016-05-06  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
 
 	* ld/testsuite/ld-srec/srec.exp: Mark test as XFAIL for AVR.
diff --git a/ld/testsuite/ld-elf/pr17550-1.s b/ld/testsuite/ld-elf/pr17550-1.s
new file mode 100644
index 0000000..3da73dc
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550-1.s
@@ -0,0 +1,9 @@
+	.section .data,"awG",%progbits,foo_group,comdat
+	.dc.a	x_alias
+	.type	x, %object
+	.p2align 2
+	.size	x, 4
+x:
+	.zero	4
+	.globl	x_alias
+	.set	x_alias,x
diff --git a/ld/testsuite/ld-elf/pr17550-2.s b/ld/testsuite/ld-elf/pr17550-2.s
new file mode 100644
index 0000000..eb4120f
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550-2.s
@@ -0,0 +1,6 @@
+	.section .data,"awG",%progbits,foo_group,comdat
+	.type	x, %object
+	.p2align 2
+	.size	x, 4
+x:
+	.zero	4
diff --git a/ld/testsuite/ld-elf/pr17550-3.s b/ld/testsuite/ld-elf/pr17550-3.s
new file mode 100644
index 0000000..3d7c252
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550-3.s
@@ -0,0 +1,14 @@
+	.data
+	.dc.a	y
+	.section .data,"awG",%progbits,foo_group,comdat
+	.type	y, %object
+	.size	y, 4
+y:
+	.zero	4
+	.globl	x
+	.type	x, %object
+	.size	x, 4
+x:
+	.zero	4
+	.globl	x_alias
+	.set	x_alias,x
diff --git a/ld/testsuite/ld-elf/pr17550-4.s b/ld/testsuite/ld-elf/pr17550-4.s
new file mode 100644
index 0000000..d0442fd
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550-4.s
@@ -0,0 +1,15 @@
+	.data
+	.dc.a	y
+	.section .data,"awG",%progbits,foo_group,comdat
+	.globl	y
+	.type	y, %object
+	.size	y, 4
+y:
+	.zero	4
+	.globl	x
+	.type	x, %object
+	.size	x, 4
+x:
+	.zero	4
+	.globl	x_alias
+	.set	x_alias,x
diff --git a/ld/testsuite/ld-elf/pr17550a.d b/ld/testsuite/ld-elf/pr17550a.d
new file mode 100644
index 0000000..c8f0424
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550a.d
@@ -0,0 +1,14 @@
+#source: pr17550-1.s
+#source: pr17550-2.s
+#ld: -r
+#readelf: -s --wide
+#notarget: alpha-*-* cr16-*-* crx-*-* d30v-*-* dlx-*-* i960-*-* pj*-*-*
+# Disabled on alpha because alpha has a different .set directive.
+# cr16 and crx use non-standard scripts with memory regions, which don't
+# play well with comdat group sections under ld -r.  Generic linker
+# targets don't support comdat group sections.
+
+#failif
+#...
+ +[0-9]+: +[0-9a-f]+ +0 +OBJECT +GLOBAL +DEFAULT +UND x_alias
+#...
diff --git a/ld/testsuite/ld-elf/pr17550b.d b/ld/testsuite/ld-elf/pr17550b.d
new file mode 100644
index 0000000..d189747
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550b.d
@@ -0,0 +1,14 @@
+#source: pr17550-2.s
+#source: pr17550-1.s
+#ld: -r
+#readelf: -s --wide
+#notarget: alpha-*-* cr16-*-* crx-*-* d30v-*-* dlx-*-* i960-*-* pj*-*-*
+# Disabled on alpha because alpha has a different .set directive.
+# cr16 and crx use non-standard scripts with memory regions, which don't
+# play well with comdat group sections under ld -r.  Generic linker
+# targets don't support comdat group sections.
+
+#failif
+#...
+ +[0-9]+: +[0-9a-f]+ +0 +OBJECT +GLOBAL +DEFAULT +UND x_alias
+#...
diff --git a/ld/testsuite/ld-elf/pr17550c.d b/ld/testsuite/ld-elf/pr17550c.d
new file mode 100644
index 0000000..23a83f1
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550c.d
@@ -0,0 +1,9 @@
+#source: pr17550-2.s
+#source: pr17550-3.s
+#ld: -r
+#error: .*: defined in discarded section `\.data\[foo_group\]'
+#notarget: alpha-*-* cr16-*-* crx-*-* d30v-*-* dlx-*-* i960-*-* pj*-*-*
+# Disabled on alpha because alpha has a different .set directive.
+# cr16 and crx use non-standard scripts with memory regions, which don't
+# play well with comdat group sections under ld -r.  Generic linker
+# targets don't support comdat group sections.
diff --git a/ld/testsuite/ld-elf/pr17550d.d b/ld/testsuite/ld-elf/pr17550d.d
new file mode 100644
index 0000000..e8fad96
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr17550d.d
@@ -0,0 +1,13 @@
+#source: pr17550-2.s
+#source: pr17550-4.s
+#ld: -r
+#readelf: -s --wide
+#notarget: alpha-*-* cr16-*-* crx-*-* d30v-*-* dlx-*-* i960-*-* pj*-*-*
+# Disabled on alpha because alpha has a different .set directive.
+# cr16 and crx use non-standard scripts with memory regions, which don't
+# play well with comdat group sections under ld -r.  Generic linker
+# targets don't support comdat group sections.
+
+#...
+ +[0-9]+: +[0-9a-f]+ +0 +OBJECT +GLOBAL +DEFAULT +UND y
+#pass