Hi,

On Tue, 2020-09-15 at 20:40 +0200, Jakub Jelinek wrote:
> Ok, here it is in patch form.
> I've briefly tested it, with the older binutils I have around (no --gdwarf-N
> support), with latest gas (--gdwarf-N that can be passed to as even when
> compiling C/C++ etc. code and emitting .debug_line) and latest gas with Mark's fix
> reverted (--gdwarf-N support, but can only pass it to as when assembling
> user .s/.S files, not when compiling C/C++ etc.).
> Will bootstrap/regtest (with the older binutils) later tonight.
> 
> 2020-09-15  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* configure.ac (HAVE_AS_GDWARF_5_DEBUG_FLAG,
> 	HAVE_AS_WORKING_DWARF_4_FLAG): New tests.
> 	* gcc.c (ASM_DEBUG_DWARF_OPTION): Define.
> 	(ASM_DEBUG_SPEC): Use ASM_DEBUG_DWARF_OPTION instead of
> 	"--gdwarf2".  Use %{cond:opt1;:opt2} style.
> 	(ASM_DEBUG_OPTION_DWARF_OPT): Define.
> 	(ASM_DEBUG_OPTION_SPEC): Define.
> 	(asm_debug_option): New variable.
> 	(asm_options): Add "%(asm_debug_option)".
> 	(static_specs): Add asm_debug_option entry.
> 	(static_spec_functions): Add dwarf-version-gt.
> 	(debug_level_greater_than_spec_func): New function.
> 	* config/darwin.h (ASM_DEBUG_OPTION_SPEC): Define.
> 	* config/darwin9.h (ASM_DEBUG_OPTION_SPEC): Redefine.
> 	* config.in: Regenerated.
> 	* configure: Regenerated.

Once this is in we can more generally emit DW_FORM_line_str for
filepaths in CU DIEs for the name and comp_dir attribute. There
currently is a bit of a hack to do this in dwarf2out_early_finish, but
that only works when the assembler doesn't emit a DWARF5 .debug_line,
but gcc does it itself.

What do you think of the attached patch?