Emit .file 0 directive earlier in DWARF 5

When the assembler supports it, the compiler automatically passes --gdwarf-5
to it, which has an interesting side effect: any assembly instruction prior
to the first .file directive defines a new line associated with .file 0 in
the .debug_line section and of course the numbering of these implicit lines
has nothing to do with that of the source code.  This can be problematic in
Ada when we do not generate .file/.loc directives for compiled-generated
functions to avoid too jumpy a debugging experience.

gcc/
	* dwarf2out.c (dwarf2out_assembly_start): Emit .file 0 marker here..
	(dwarf2out_finish): ...instead of here.

1 files changed, 24 insertions, 21 deletions

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 88eb3f9..9a91981 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -29363,6 +29363,30 @@ dwarf2out_assembly_start (void)
       && dwarf2out_do_cfi_asm ()
       && !dwarf2out_do_eh_frame ())
     fprintf (asm_out_file, "\t.cfi_sections\t.debug_frame\n");
+
+#if defined(HAVE_AS_GDWARF_5_DEBUG_FLAG) && defined(HAVE_AS_WORKING_DWARF_N_FLAG)
+  if (output_asm_line_debug_info () && dwarf_version >= 5)
+    {
+      /* When gas outputs DWARF5 .debug_line[_str] then we have to
+	 tell it the comp_dir and main file name for the zero entry
+	 line table.  */
+      const char *comp_dir, *filename0;
+
+      comp_dir = comp_dir_string ();
+      if (comp_dir == NULL)
+	comp_dir = "";
+
+      filename0 = get_AT_string (comp_unit_die (), DW_AT_name);
+      if (filename0 == NULL)
+	filename0 = "";
+
+      fprintf (asm_out_file, "\t.file 0 ");
+      output_quoted_string (asm_out_file, remap_debug_filename (comp_dir));
+      fputc (' ', asm_out_file);
+      output_quoted_string (asm_out_file, remap_debug_filename (filename0));
+      fputc ('\n', asm_out_file);
+    }
+#endif
 }
 
 /* A helper function for dwarf2out_finish called through
@@ -32315,27 +32339,6 @@ dwarf2out_finish (const char *filename)
   ASM_OUTPUT_LABEL (asm_out_file, debug_line_section_label);
   if (! output_asm_line_debug_info ())
     output_line_info (false);
-  else if (asm_outputs_debug_line_str ())
-    {
-      /* When gas outputs DWARF5 .debug_line[_str] then we have to
-	 tell it the comp_dir and main file name for the zero entry
-	 line table.  */
-      const char *comp_dir, *filename0;
-
-      comp_dir = comp_dir_string ();
-      if (comp_dir == NULL)
-	comp_dir = "";
-
-      filename0 = get_AT_string (comp_unit_die (), DW_AT_name);
-      if (filename0 == NULL)
-	filename0 = "";
-
-      fprintf (asm_out_file, "\t.file 0 ");
-      output_quoted_string (asm_out_file, remap_debug_filename (comp_dir));
-      fputc (' ', asm_out_file);
-      output_quoted_string (asm_out_file, remap_debug_filename (filename0));
-      fputc ('\n', asm_out_file);
-    }
 
   if (dwarf_split_debug_info && info_section_emitted)
     {