[RFC][debug] Add -greadable-dwarf

[Jason Merrill]

How about adding this name to a -dA comment instead of the actual dwarf?

On Tue, Aug 21, 2018, 12:59 AM Richard Biener <rguenther@suse.de> wrote:

> On Wed, 15 Aug 2018, Tom de Vries wrote:
>
> > Hi,
> >
> > This patch adds option -greadable-dwarf.  In absence of an DW_AT_comment
> > attribute,
>
> What's a DW_AT_comment attribute?  I don't see this mentioned in the
> patch.
>
> > it sets the DW_AT_name attribute of dies that otherwise do not get
> > that attribute, to make it easier to figure out what the die is
> describing.
> >
> > The option exports the names of artificial variables:
> > ...
> >  DIE    0: DW_TAG_variable (0x7fa934dd54b0)
> > +  DW_AT_name: "D.1922"
> >    DW_AT_type: die -> 0 (0x7fa934dd0d70)
> >    DW_AT_artificial: 1
> >
> > ...
> > which can be traced back to gimple dumps:
> > ...
> >   char a[0:D.1922] [value-expr: *a.0];
> > ...
> >
> > Furthermore, it adds names to external references:
> > ...
> >  DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)
> > +DW_AT_name: "main"
> >  DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29
> (0x7fa88b965140)
> > ...
> >
> > This is an undocumented developer-only option, because using this option
> may
> > change behaviour of dwarf consumers, f.i., gdb shows the artificial
> variables:
> > ...
> > (gdb) info locals
> > a = 0x7fffffffda90 "\005"
> > D.4278 = <optimized out>
> > ...
> >
> > Any comments?
>
> The idea is OK I guess but I'd call it -gforce-named-dies instead
> of -greadable-dwarf.  It also goes only half-way since it doesn't
> add names to DECL_NAMELESS vars.
>
> There doesn't seem to be a convenient place to
>
> > Thanks,
> > - Tom
> >
> > [debug] Add -greadable-dwarf
> >
> > 2018-08-15  Tom de Vries  <tdevries@suse.de>
> >
> >       * common.opt (greadable-dwarf): Add option.
> >       * dwarf2out.c (add_name_and_src_coords_attributes): Add param. Add
> name
> >       for artifical decls.
> >       (add_decl_name): New function.
> >       (dwarf2out_register_external_die): Add name to external reference
> die.
> >
> > ---
> >  gcc/common.opt  |  5 +++++
> >  gcc/dwarf2out.c | 24 +++++++++++++++++++++---
> >  2 files changed, 26 insertions(+), 3 deletions(-)
> >
> > diff --git a/gcc/common.opt b/gcc/common.opt
> > index b2f2215ecc6..6e5e0558e49 100644
> > --- a/gcc/common.opt
> > +++ b/gcc/common.opt
> > @@ -2972,6 +2972,11 @@ gstrict-dwarf
> >  Common Driver Report Var(dwarf_strict) Init(0)
> >  Don't emit DWARF additions beyond selected version.
> >
> > +greadable-dwarf
> > +Common Driver Undocumented Report Var(flag_readable_dwarf) Init(0)
> > +Make generated dwarf more readable, at the cost of space and exposing
> compiler
> > +internals.
> > +
> >  gtoggle
> >  Common Driver Report Var(flag_gtoggle)
> >  Toggle debug information generation.
> > diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
> > index 4b63cbd8a1e..8c6b4372874 100644
> > --- a/gcc/dwarf2out.c
> > +++ b/gcc/dwarf2out.c
> > @@ -3824,7 +3824,9 @@ static void add_prototyped_attribute (dw_die_ref,
> tree);
> >  static dw_die_ref add_abstract_origin_attribute (dw_die_ref, tree);
> >  static void add_pure_or_virtual_attribute (dw_die_ref, tree);
> >  static void add_src_coords_attributes (dw_die_ref, tree);
> > -static void add_name_and_src_coords_attributes (dw_die_ref, tree, bool
> = false);
> > +static void add_name_and_src_coords_attributes (dw_die_ref, tree, bool
> = false,
> > +                                             bool = false);
> > +static void add_decl_name (dw_die_ref, tree);
> >  static void add_discr_value (dw_die_ref, dw_discr_value *);
> >  static void add_discr_list (dw_die_ref, dw_discr_list_ref);
> >  static inline dw_discr_list_ref AT_discr_list (dw_attr_node *);
> > @@ -6022,6 +6024,8 @@ dwarf2out_register_external_die (tree decl, const
> char *sym,
> >    else
> >      equate_decl_number_to_die (decl, die);
> >
> > +  if (flag_readable_dwarf)
> > +    add_decl_name (die, decl);
>
> Please use add_name_and_src_coords_attributes directly.
>
> >    /* Add a reference to the DIE providing early debug at $sym + off.  */
> >    add_AT_external_die_ref (die, DW_AT_abstract_origin, sym, off);
> >  }
> > @@ -21269,7 +21273,8 @@ add_linkage_name (dw_die_ref die, tree decl)
> >
> >  static void
> >  add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
> > -                                 bool no_linkage_name)
> > +                                 bool no_linkage_name,
> > +                                 bool no_src_coords_attributes)
> >  {
> >    tree decl_name;
> >
> > @@ -21279,12 +21284,19 @@ add_name_and_src_coords_attributes (dw_die_ref
> die, tree decl,
> >        const char *name = dwarf2_name (decl, 0);
> >        if (name)
> >       add_name_attribute (die, name);
> > -      if (! DECL_ARTIFICIAL (decl))
> > +      if (!no_src_coords_attributes && ! DECL_ARTIFICIAL (decl))
>
> inconsistent spacing after !
>
> >       add_src_coords_attributes (die, decl);
> >
> >        if (!no_linkage_name)
> >       add_linkage_name (die, decl);
> >      }
> > +  else if (flag_readable_dwarf && decl_name == NULL)
> > +    {
> > +      char *buf = XNEWVEC (char, 32);
> > +      char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';
> > +      sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));
> > +      add_name_attribute (die, buf);
>
> I think you leak 'buf'.
>
> > +    }
> >
> >  #ifdef VMS_DEBUGGING_INFO
>
> how does it interact with this VMS_DEBUGGING_INFO path?
>
> >    /* Get the function's name, as described by its RTL.  This may be
> different
> > @@ -21298,6 +21310,12 @@ add_name_and_src_coords_attributes (dw_die_ref
> die, tree decl,
> >  #endif /* VMS_DEBUGGING_INFO */
> >  }
> >
> > +static void
> > +add_decl_name (dw_die_ref die, tree decl)
> > +{
> > +  add_name_and_src_coords_attributes (die, decl, true, true);
> > +}
> > +
> >  /* Add VALUE as a DW_AT_discr_value attribute to DIE.  */
> >
> >  static void
> >
> >
>
> --
> Richard Biener <rguenther@suse.de>
> SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
> 21284 (AG Nuernberg)
>