Re: [PATCH 1/2] Fix debug info for ignored decls at start of assembly

[Richard Biener <rguenther@suse.de>]

On Mon, 26 Jul 2021, Bernd Edlinger wrote:

> Ignored functions decls that are compiled at the start of
> the assembly have bogus line numbers until the first .file
> directive, as reported in PR101575.
> 
> The work around for this issue is to emit a dummy .file
> directive when the first function is DECL_IGNORED_P, when
> that is not already done, mostly for -fdwarf-4.

I wonder if it makes sense to unconditionally announce the
TU with a .file directive at the beginning.  ISTR this is
what we now do with -gdwarf-5.

Note get_AT_string (comp_unit_die (), DW_AT_name) doesn't
work with LTO, you'll get <dummy> then.

Is the dwarf assembler bug reported/fixed?  Can you include
a reference please?

Thanks,
Richard.

> 2021-07-24  Bernd Edlinger  <bernd.edlinger@hotmail.de>
> 
> 	PR ada/101575
> 	* dwarf2out.c (dwarf2out_begin_prologue): Move init
> 	of fde->ignored_debug to dwarf2out_set_ignored_loc.
> 	(dwarf2out_set_ignored_loc): This is now also called
> 	when no .loc statement is to be generated, in that case
> 	we emit a dummy .file statement when needed.
> 	* final.c (final_start_function_1,
> 	final_scan_insn_1): Call debug_hooks->set_ignored_loc
> 	for all DECL_IGNORED_P functions.
> ---
>  gcc/dwarf2out.c | 29 +++++++++++++++++++++++++----
>  gcc/final.c     |  5 ++---
>  2 files changed, 27 insertions(+), 7 deletions(-)
> 
> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> index 884f1e1..8de0d6f 100644
> --- a/gcc/dwarf2out.c
> +++ b/gcc/dwarf2out.c
> @@ -1115,7 +1115,6 @@ dwarf2out_begin_prologue (unsigned int line ATTRIBUTE_UNUSED,
>    fde->dw_fde_current_label = dup_label;
>    fde->in_std_section = (fnsec == text_section
>  			 || (cold_text_section && fnsec == cold_text_section));
> -  fde->ignored_debug = DECL_IGNORED_P (current_function_decl);
>    in_text_section_p = fnsec == text_section;
>  
>    /* We only want to output line number information for the genuine dwarf2
> @@ -28546,10 +28545,32 @@ dwarf2out_set_ignored_loc (unsigned int line, unsigned int column,
>  {
>    dw_fde_ref fde = cfun->fde;
>  
> -  fde->ignored_debug = false;
> -  set_cur_line_info_table (function_section (fde->decl));
> +  if (filename)
> +    {
> +      set_cur_line_info_table (function_section (fde->decl));
> +
> +      dwarf2out_source_line (line, column, filename, 0, true);
> +    }
> +  else
> +    {
> +      fde->ignored_debug = true;
> +
> +      /* Work around for PR101575: output a dummy .file directive.  */
> +      if (in_first_function_p
> +	  && debug_info_level >= DINFO_LEVEL_TERSE
> +	  && dwarf_debuginfo_p ()
> +#if defined(HAVE_AS_GDWARF_5_DEBUG_FLAG) && defined(HAVE_AS_WORKING_DWARF_N_FLAG)
> +	  && dwarf_version <= 4
> +#endif
> +	  && output_asm_line_debug_info ())
> +	{
> +	  const char *filename0 = get_AT_string (comp_unit_die (), DW_AT_name);
>  
> -  dwarf2out_source_line (line, column, filename, 0, true);
> +	  if (filename0 == NULL)
> +	    filename0 = "<dummy>";
> +	  maybe_emit_file (lookup_filename (filename0));
> +	}
> +    }
>  }
>  
>  /* Record the beginning of a new source file.  */
> diff --git a/gcc/final.c b/gcc/final.c
> index ac6892d..82a5767 100644
> --- a/gcc/final.c
> +++ b/gcc/final.c
> @@ -1725,7 +1725,7 @@ final_start_function_1 (rtx_insn **firstp, FILE *file, int *seen,
>    if (!dwarf2_debug_info_emitted_p (current_function_decl))
>      dwarf2out_begin_prologue (0, 0, NULL);
>  
> -  if (DECL_IGNORED_P (current_function_decl) && last_linenum && last_filename)
> +  if (DECL_IGNORED_P (current_function_decl))
>      debug_hooks->set_ignored_loc (last_linenum, last_columnnum, last_filename);
>  
>  #ifdef LEAF_REG_REMAP
> @@ -2205,8 +2205,7 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int optimize_p ATTRIBUTE_UNUSED,
>  	    }
>  	  else if (!DECL_IGNORED_P (current_function_decl))
>  	    debug_hooks->switch_text_section ();
> -	  if (DECL_IGNORED_P (current_function_decl) && last_linenum
> -	      && last_filename)
> +	  if (DECL_IGNORED_P (current_function_decl))
>  	    debug_hooks->set_ignored_loc (last_linenum, last_columnnum,
>  					  last_filename);
>  
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)