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Re: [PATCH][debug] Add -gdescriptive-dies
On Wed, 22 Aug 2018, Tom de Vries wrote:
> [ was: Re: [PATCH][debug] Add -gforce-named-dies ]
>
> On 08/22/2018 11:46 AM, Tom de Vries wrote:
> > On 08/22/2018 08:56 AM, Tom de Vries wrote:
> >> 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>
> >> ...
> > I just found in the dwarf 5 spec the attribute DW_AT_description
> > (present since version 3):
> > ...
> > 2.20 Entity Descriptions
> > Some debugging information entries may describe entities in the program
> > that are artificial, or which otherwise have a “name” that is not a
> > valid identifier in the programming language.
> >
> > This attribute provides a means for the producer to indicate the purpose
> > or usage of the containing debugging infor
> >
> > Generally, any debugging information entry that has, or may have, a
> > DW_AT_name attribute, may also have a DW_AT_description attribute whose
> > value is a null-terminated string providing a description of the entity.
> >
> > It is expected that a debugger will display these descriptions as part
> > of displaying other properties of an entity.
> > ...
> >
> > AFAICT, gdb currently does not explicitly handle this attribute, which I
> > think means it's ignored.
> >
> > It seems applicable to use DW_AT_description at least for the artificial
> > decls.
> >
> > Perhaps even for all cases that are added by the patch?
> >
>
> I've chosen for this option. Using DW_AT_desciption instead of
> DW_AT_name should minimize difference in gdb behaviour with and without
> -gdescriptive-dies.
-gdescribe-dies?
> > I'll rewrite the patch.
>
> OK for trunk?
Few comments:
+static void
+add_desc_attribute (dw_die_ref die, tree decl)
+{
+ tree decl_name;
+
+ if (!flag_descriptive_dies || dwarf_version < 3)
+ return;
+
you said this is a DWARF5 "feature", I'd suggest changing the
check to
if (!flag_desctiprive_dies || (dwarf_version < 5 && dwarf_strict))
given -gdescribe-dies is enough of a user request to enable the
feature. Not sure if we should warn about -gstrict-dwarf
combination with it and -gdwarf-N < 5.
+ else if (TREE_CODE (decl) == VAR_DECL || TREE_CODE (decl) ==
CONST_DECL)
+ {
+ char buf[32];
+ char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';
+ sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));
+ add_desc_attribute (die, buf);
+ }
I wondered before if we can use pretty-printing of decl here. At
least I wouldn't restrict it to VAR_DECLs, FUNCTION_DECLs can
certainly appear here I think.
+@item -gdescriptive-dies
+@opindex gdescriptive-dies
+Add description attribute to DWARF DIEs that have no name attribute.
+
Either "description attributes" or "a description attribute", not
100% sure being a non-native speaker.
Otherwise the patch looks OK to me but please leave Jason time
to comment.
Richard.