Re: Duplicate .debug_lines (Was: [PATCH 5/5] Add --gdwarf-5 to ASM_SPEC)

[Mark Wielaard <mark@klomp.org>]

Hi,

On Wed, Aug 26, 2020 at 04:38:21PM -0700, H.J. Lu wrote:
> On Wed, Aug 26, 2020 at 2:38 PM Mark Wielaard <mark@klomp.org> wrote:
> > Would it be possible to have something like the following in gas, so
> > that it doesn't try generating a .debug_line section if there already
> > is one, even when -gdwarf-N is given (unless the assembly also
> > contains .loc directives because that shows the user is really
> > confused)?
> >
> > diff --git a/gas/dwarf2dbg.c b/gas/dwarf2dbg.c
> > index e4ba56d82ba..c0c09f4e9d0 100644
> > --- a/gas/dwarf2dbg.c
> > +++ b/gas/dwarf2dbg.c
> > @@ -2626,7 +2626,7 @@ dwarf2_init (void)
> >
> >
> >  /* Finish the dwarf2 debug sections.  We emit .debug.line if there
> > -   were any .file/.loc directives, or --gdwarf2 was given, or if the
> > +   were any .file/.loc directives, or --gdwarf2 was given, and if the
> >     file has a non-empty .debug_info section and an empty .debug_line
> >     section.  If we emit .debug_line, and the .debug_info section is
> >     empty, we also emit .debug_info, .debug_aranges and .debug_abbrev.
> > @@ -2650,9 +2650,16 @@ dwarf2_finish (void)
> >    empty_debug_line = line_seg == NULL || !seg_not_empty_p (line_seg);
> >
> >    /* We can't construct a new debug_line section if we already have one.
> > -     Give an error.  */
> > +     Give an error if we have seen any .loc, otherwise trust the user
> > +     knows what they are doing and want to generate the .debug_line
> > +     (and all other debug sections) themselves.  */
> >    if (all_segs && !empty_debug_line)
> > -    as_fatal ("duplicate .debug_line sections");
> > +    {
> > +      if (dwarf2_loc_directive_seen)
> > +       as_fatal ("duplicate .debug_line sections");
> > +      else
> > +       return;
> > +    }
> >
> >    if ((!all_segs && emit_other_sections)
> >        || (!emit_other_sections && !empty_debug_line))
> >
>
> I have run into this issue before.  "as -g" shouldn't silently
> generate incorrect debug info when input assembly codes already
> contain debug directives.  AS should either issue an error or
> ignore -g.

Right, that is what this patch does for .debug_line.  gas already
doesn't generate .debug_info, .debug_aranges and .debug_abbrev if
.debug_info is non-empty, even if -g is given.

> In either case, we need a testcase  to verify it.

Right, and the documentation needs to be update.  But first we have to
know whether the gas maintainers think this is the right approach.

Cheers,

Mark