[gcc r11-6868] dwarf2out: Always emit required 0 entries for DWARF 5 in *.debug_line [PR98796]

[gcc r11-6868] dwarf2out: Always emit required 0 entries for DWARF 5 in *.debug_line [PR98796]

[Jakub Jelinek]

https://gcc.gnu.org/g:b485fa167ef35c8facbd7c21cb86fd1abc77efcf

commit r11-6868-gb485fa167ef35c8facbd7c21cb86fd1abc77efcf
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jan 22 22:37:36 2021 +0100

    dwarf2out: Always emit required 0 entries for DWARF 5 in *.debug_line [PR98796]
    
    When GCC is emitting .debug_line or .gnu.debuglto_.debug_line section by
    itself (happens either with too old or non-GNU assembler, with
    -gno-as-loc-support or with -flto) on empty translation units, it violates
    the DWARF 5 requirements.
    The standard says:
    "The first entry is the current directory of the compilation."
    and a few lines later:
    "The first entry in the sequence is the primary source file whose file name
    exactly matches that given in the DW_AT_name attribute in the compilation
    unit debugging information entry."
    GCC emits 4 zeros (directory entry format count, directories count,
    filename entry format count and filename count), which would be ok if the
    spec said The first entry may be rather than is.
    
    I had a brief look at whether I could just fall through into the rest of the
    function, but there are too many assumptions that there is at least one
    normal file that it can't be done that way easily.
    
    So this patch instead extends the early out code to emit the required
    minimum, which is 15 bytes more than we used to emit before.
    
    2021-01-22  Jakub Jelinek  <jakub@redhat.com>
    
            PR debug/98796
            * dwarf2out.c (output_file_names): For -gdwarf-5, if there are no
            filenames to emit, still emit the required 0 index directory and
            filename entries that match DW_AT_comp_dir and DW_AT_name of the
            compilation unit.

Diff:
---
 gcc/dwarf2out.c | 48 ++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 44 insertions(+), 4 deletions(-)

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 77ea4948d5e..2ec3449a190 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -12252,10 +12252,50 @@ output_file_names (void)
     {
       if (dwarf_version >= 5)
 	{
-	  dw2_asm_output_data (1, 0, "Directory entry format count");
-	  dw2_asm_output_data_uleb128 (0, "Directories count");
-	  dw2_asm_output_data (1, 0, "File name entry format count");
-	  dw2_asm_output_data_uleb128 (0, "File names count");
+	  const char *comp_dir = comp_dir_string ();
+	  if (comp_dir == NULL)
+	    comp_dir = "";
+	  dw2_asm_output_data (1, 1, "Directory entry format count");
+	  enum dwarf_form str_form = DW_FORM_string;
+	  if (DWARF5_USE_DEBUG_LINE_STR)
+	    str_form = DW_FORM_line_strp;
+	  dw2_asm_output_data_uleb128 (DW_LNCT_path, "DW_LNCT_path");
+	  dw2_asm_output_data_uleb128 (str_form, "%s",
+				       get_DW_FORM_name (str_form));
+	  dw2_asm_output_data_uleb128 (1, "Directories count");
+	  if (str_form == DW_FORM_string)
+	    dw2_asm_output_nstring (comp_dir, -1, "Directory Entry: %#x", 0);
+	  else
+	    output_line_string (str_form, comp_dir, "Directory Entry", 0);
+	  const char *filename0 = get_AT_string (comp_unit_die (), DW_AT_name);
+	  if (filename0 == NULL)
+	    filename0 = "";
+#ifdef VMS_DEBUGGING_INFO
+	  dw2_asm_output_data (1, 4, "File name entry format count");
+#else
+	  dw2_asm_output_data (1, 2, "File name entry format count");
+#endif
+	  dw2_asm_output_data_uleb128 (DW_LNCT_path, "DW_LNCT_path");
+	  dw2_asm_output_data_uleb128 (str_form, "%s",
+				       get_DW_FORM_name (str_form));
+	  dw2_asm_output_data_uleb128 (DW_LNCT_directory_index,
+				       "DW_LNCT_directory_index");
+	  dw2_asm_output_data_uleb128 (DW_FORM_data1, "%s",
+				       get_DW_FORM_name (DW_FORM_data1));
+#ifdef VMS_DEBUGGING_INFO
+	  dw2_asm_output_data_uleb128 (DW_LNCT_timestamp, "DW_LNCT_timestamp");
+	  dw2_asm_output_data_uleb128 (DW_FORM_udata, "DW_FORM_udata");
+	  dw2_asm_output_data_uleb128 (DW_LNCT_size, "DW_LNCT_size");
+	  dw2_asm_output_data_uleb128 (DW_FORM_udata, "DW_FORM_udata");
+#endif
+	  dw2_asm_output_data_uleb128 (1, "File names count");
+
+	  output_line_string (str_form, filename0, "File Entry", 0);
+	  dw2_asm_output_data (1, 0, NULL);
+#ifdef VMS_DEBUGGING_INFO
+	  dw2_asm_output_data_uleb128 (0, NULL);
+	  dw2_asm_output_data_uleb128 (0, NULL);
+#endif
 	}
       else
 	{