Re-introduce '_start' labels and add alignment in dw2-dir-file-name test case.

On ppc64-linux a function symbol does not point to code, but to the
function descriptor.  Thus the previous change for this test case
broke it:

      https://sourceware.org/ml/gdb-patches/2014-01/msg00275.html

This patch reverts to the original method, re-introducing '_start'
symbols.  In addition, it adds sufficient alignment before the label,
such that the label never points into an alignment gap.

gdb/testsuite/ChangeLog:
	* gdb.dwarf2/dw2-dir-file-name.c (FUNC): Insert alignment and
	define "*_start" label.  Make "name" static.
	* gdb.dwarf2/dw2-dir-file-name.exp: Replace references to
	${name} by references to ${name}_start.

gdb/testsuite/ChangeLog

@@ -1,3 +1,10 @@
+2014-01-22  Andreas Arnez  <arnez@vnet.linux.ibm.com>
+
+	* gdb.dwarf2/dw2-dir-file-name.c (FUNC): Insert alignment and
+	define "*_start" label.  Make "name" static.
+	* gdb.dwarf2/dw2-dir-file-name.exp: Replace references to
+	${name} by references to ${name}_start.
+
 2014-01-22  Andreas Arnez  <arnez@vnet.linux.ibm.com>
 
 	* gdb.base/info-macros.exp: Remove "debug" from the compile

gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c

@@ -63,8 +63,16 @@ FUNC (compdir_absolute_ldir_absolute_file_relative_different)	\
 FUNC (compdir_absolute_ldir_absolute_file_absolute_same)	\
 FUNC (compdir_absolute_ldir_absolute_file_absolute_different)
 
+/* Notes: (1) The '*_start' label below is needed because 'name' may
+   point to a function descriptor instead of to the actual code.  (2)
+   The '.balign' should specify the highest possible function
+   alignment across all supported architectures, such that the label
+   never points into the alignment gap.  */
+
 #define FUNC(name)					\
-  void							\
+  asm (".balign 8");					\
+  asm (#name "_start: .globl " #name "_start\n");	\
+  static void						\
   name (void)						\
   {							\
     v++;						\

gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp

@@ -54,7 +54,7 @@ proc out_cu { name cu_dir cu_name line_dir line_name } {
 	.ascii	\"GNU C\\0\"			/* DW_AT_producer */
 	.byte	2				/* DW_AT_language (DW_LANG_C) */
 	.4byte	.Lline_${name}_begin		/* DW_AT_stmt_list */
-	.4byte	${name}			/* DW_AT_low_pc */
+	.4byte	${name}_start			/* DW_AT_low_pc */
 	.4byte	${name}_end			/* DW_AT_high_pc */
 "
     if { $cu_dir != "" } {
@@ -65,7 +65,7 @@ proc out_cu { name cu_dir cu_name line_dir line_name } {
 
 	.uleb128	3			/* Abbrev: DW_TAG_subprogram */
 	.asciz		\"${name}\"		/* DW_AT_name */
-	.4byte		${name}		/* DW_AT_low_pc */
+	.4byte		${name}_start		/* DW_AT_low_pc */
 	.4byte		${name}_end		/* DW_AT_high_pc */
 
 	.byte		0			/* End of children of CU */
@@ -122,7 +122,7 @@ proc out_line { name cu_dir cu_name line_dir line_name } {
 	.byte		0	/* DW_LNE_set_address */
 	.uleb128	5
 	.byte		2
-	.4byte		${name}
+	.4byte		${name}_start
 	.byte		1	/* DW_LNS_copy */
 	.byte		3	/* DW_LNS_advance_line */
 	.sleb128	1	/* ... to 1000 */