Also disallow global alias of common symbol

We can't create alias of common symbol.  Local alias of common symbol has
been disallowed.  But global alias of common symbol is disallowed when the
common symbol is seen first and silently dropped otherwise.  This patch
disallows alias of common symbol in all cases.

gas/

	PR gas/21667
	* read.c (pseudo_set): Update error message for alias of common
	symbol.
	* write.c (write_object_file): Disallow both local and global
	aliases of common symbol.
	* testsuite/gas/elf/common5a.d: New file.
	* testsuite/gas/elf/common5a.l: Likewise.
	* testsuite/gas/elf/common5a.s: Likewise.
	* testsuite/gas/elf/common5b.d: Likewise.
	* testsuite/gas/elf/common5b.l: Likewise.
	* testsuite/gas/elf/common5b.s: Likewise.
	* testsuite/gas/elf/common5c.d: Likewise.
	* testsuite/gas/elf/common5c.s: Likewise.
	* testsuite/gas/elf/common5d.d: Likewise.
	* testsuite/gas/elf/common5d.s: Likewise.
	* testsuite/gas/elf/elf.exp: Run common5a, common5b, common5c
	and common5d.

gas/ChangeLog

@@ -1,3 +1,23 @@
+2017-08-11  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR gas/21667
+	* read.c (pseudo_set): Update error message for alias of common
+	symbol.
+	* write.c (write_object_file): Disallow both local and global
+	aliases of common symbol.
+	* testsuite/gas/elf/common5a.d: New file.
+	* testsuite/gas/elf/common5a.l: Likewise.
+	* testsuite/gas/elf/common5a.s: Likewise.
+	* testsuite/gas/elf/common5b.d: Likewise.
+	* testsuite/gas/elf/common5b.l: Likewise.
+	* testsuite/gas/elf/common5b.s: Likewise.
+	* testsuite/gas/elf/common5c.d: Likewise.
+	* testsuite/gas/elf/common5c.s: Likewise.
+	* testsuite/gas/elf/common5d.d: Likewise.
+	* testsuite/gas/elf/common5d.s: Likewise.
+	* testsuite/gas/elf/elf.exp: Run common5a, common5b, common5c
+	and common5d.
+
 2017-08-10  Nick Clifton  <nickc@redhat.com>
 
 	PR gas/21939

gas/read.c

@@ -3870,7 +3870,7 @@ pseudo_set (symbolS *symbolP)
 	  symbolS *s = exp.X_add_symbol;
 
 	  if (S_IS_COMMON (s))
-	    as_bad (_("`%s' can't be equated to common symbol '%s'"),
+	    as_bad (_("`%s' can't be equated to common symbol `%s'"),
 		    S_GET_NAME (symbolP), S_GET_NAME (s));
 
 	  S_SET_SEGMENT (symbolP, seg);

gas/testsuite/gas/elf/common5a.d

@@ -0,0 +1,5 @@
+#source: common5a.s
+#as: 
+#error-output: common5a.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.

gas/testsuite/gas/elf/common5a.l

@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+[^:]*: Error: `foo1' can't be equated to common symbol `foo'

gas/testsuite/gas/elf/common5a.s

@@ -0,0 +1,3 @@
+	.set	foo1,foo
+	.globl	foo1
+	.comm	foo,8,8

gas/testsuite/gas/elf/common5b.d

@@ -0,0 +1,5 @@
+#source: common5b.s
+#as: 
+#error-output: common5b.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.

gas/testsuite/gas/elf/common5b.l

@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+[^:]*:2: Error: `foo1' can't be equated to common symbol `foo'

gas/testsuite/gas/elf/common5b.s

@@ -0,0 +1,3 @@
+	.comm	foo,8,8
+	.set	foo1,foo
+	.globl	foo1

gas/testsuite/gas/elf/common5c.d

@@ -0,0 +1,5 @@
+#source: common5c.s
+#as: 
+#error-output: common5a.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.

gas/testsuite/gas/elf/common5c.s

@@ -0,0 +1,2 @@
+	.set	foo1,foo
+	.comm	foo,8,8

gas/testsuite/gas/elf/common5d.d

@@ -0,0 +1,5 @@
+#source: common5d.s
+#as: 
+#error-output: common5b.l
+#not-target: alpha-*-*
+# The Alpha target uses its own .set pseudo-insn.

gas/testsuite/gas/elf/common5d.s

@@ -0,0 +1,2 @@
+	.comm	foo,8,8
+	.set	foo1,foo

gas/testsuite/gas/elf/elf.exp

@@ -252,6 +252,10 @@ if { [is_elf_format] } then {
 	run_dump_test "common3b"
 	run_dump_test "common4a"
 	run_dump_test "common4b"
+	run_dump_test "common5a"
+	run_dump_test "common5b"
+	run_dump_test "common5c"
+	run_dump_test "common5d"
     }
 
     run_dump_test "strtab"

gas/write.c

@@ -2107,12 +2107,11 @@ write_object_file (void)
 
 	      if (S_IS_COMMON (symp)
 		  && !TC_FAKE_LABEL (sname)
-		  && !S_IS_WEAKREFR (symp)
+		  && !S_IS_WEAKREFR (symp))
-		  && (!S_IS_EXTERNAL (symp) || S_IS_LOCAL (symp)))
 		{
 		  expressionS *e = symbol_get_value_expression (symp);
 
-		  as_bad (_("Local symbol `%s' can't be equated to common symbol `%s'"),
+		  as_bad (_("`%s' can't be equated to common symbol `%s'"),
 			  sname, S_GET_NAME (e->X_add_symbol));
 		}
 	      if (S_GET_SEGMENT (symp) == reg_section)