libbacktrace patch committed: Don't special case file 0

[Ian Lance Taylor via Gcc-patches]

This libbacktrace patch stops special casing file 0.  It's no longer
necessary as for DWARF 5 support we now set up filename 0 in all
cases.  Bootstrapped and ran libbacktrace and Go tests on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

* dwarf.c (read_line_program): Don't special case file 0.
(read_function_entry): Likewise.

b3176ab8787a7f988a931e26bce9227edd2e6d1a
diff --git a/libbacktrace/dwarf.c b/libbacktrace/dwarf.c
index 546b4b26a32..e6b1f238cd3 100644
--- a/libbacktrace/dwarf.c
+++ b/libbacktrace/dwarf.c
@@ -2857,20 +2857,15 @@ read_line_program (struct backtrace_state *state, 
struct dwarf_data *ddata,
                uint64_t fileno;
 
                fileno = read_uleb128 (line_buf);
-               if (fileno == 0)
-                 filename = "";
-               else
+               if (fileno >= hdr->filenames_count)
                  {
-                   if (fileno >= hdr->filenames_count)
-                     {
-                       dwarf_buf_error (line_buf,
-                                        ("invalid file number in "
-                                         "line number program"),
-                                        0);
-                       return 0;
-                     }
-                   filename = hdr->filenames[fileno];
+                   dwarf_buf_error (line_buf,
+                                    ("invalid file number in "
+                                     "line number program"),
+                                    0);
+                   return 0;
                  }
+               filename = hdr->filenames[fileno];
              }
              break;
            case DW_LNS_set_column:
@@ -3298,21 +3293,15 @@ read_function_entry (struct backtrace_state *state, 
struct dwarf_data *ddata,
                case DW_AT_call_file:
                  if (val.encoding == ATTR_VAL_UINT)
                    {
-                     if (val.u.uint == 0)
-                       function->caller_filename = "";
-                     else
+                     if (val.u.uint >= lhdr->filenames_count)
                        {
-                         if (val.u.uint >= lhdr->filenames_count)
-                           {
-                             dwarf_buf_error (unit_buf,
-                                              ("invalid file number in "
-                                               "DW_AT_call_file attribute"),
-                                              0);
-                             return 0;
-                           }
-                         function->caller_filename =
-                           lhdr->filenames[val.u.uint];
+                         dwarf_buf_error (unit_buf,
+                                          ("invalid file number in "
+                                           "DW_AT_call_file attribute"),
+                                          0);
+                         return 0;
                        }
+                     function->caller_filename = lhdr->filenames[val.u.uint];
                    }
                  break;