[Dwarf-discuss] 2.12.1, Non-defining Declarations
Mon May 16 19:21:33 PDT 2005
"Bishop, John E" <john.e.bishop at intel.com> writes:
> Maybe I'm missing something, but it looks like
> it says that if this DIE for a non-defining declaration,
> then it has the DW_AT_declaration attribute.
> Presumably if it's not a non-defining declaration,
> it doesn't have the DW_AT_declaration attribute.
> So why does the attribute need a flag value? Isn't
> having the attribute enough?
The description of the 'flag' form in chapter 7 says:
A flag is represented as a single byte of data (DW_FROM_flag). If
the flag has value zero, it indicates the absence of the
attribute. If the flag has a non-zero value, it indicates the
presence of the attribute.
So I think that text (2.12.1 Non-Defining Declarations) is meant to read:
If a debugging information entry has a DW_AT_declaration attribute
whose value is a true flag, then that entry represents a
non-defining or otherwise incomplete declaration of a program
It's my impression that Dwarf generally didn't require information,
but if the intent was to require DW_AT_declaration attributes on such
entries, we could say:
Debugging information entries that represent non-defining or
otherwise incomplete declarations for a program entity must have a
DW_AT_declaration attribute, whose value is a true flag.
That aside, you're suggesting something kind of interesting: an
attribute whose presence alone indicates something. We could have a
new form, DW_FORM_none, meaning that the attribute had *no* data in
the DIE itself. You'd be effectively packing the information into the
I wonder, though, if this might make life harder for simple Dwarf
producers: instead of being able to statically assign an abbrev for
each kind of die you write out, you would need to dynamically assign
abbrevs for each combination of DW_FORM_none flags you needed to write
out. With DW_FORM_flag, you can always write out a zero.
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