[dmd-internals] Fwd: DWARF issue 100504, "Extensions for D arrays, associative arrays, and delegates"

[Robert Clipsham]

Hi all,

It's been a few years since I last did some real work on DWARF in dmd
(v2.044/2.045), other than touching on OS Xes debug info not too long ago.

At the time I submitted the following enhancement request for the DWARF
specification:

http://www.dwarfstd.org/ShowIssue.php?issue=100504.1

I know that some work on debug info has been done since then - does anyone
have any input they want to add to this?

Now would be a great time to map out any and all extensions that D needs so
they can be included for a future DWARF version.

You can see the forwarded message below.

Thanks,

Robert

---------- Forwarded message ----------
From: Bishop, John E <john.e.bishop at intel.com>
Date: 26 March 2012 21:11
Subject: DWARF issue 100504, "Extensions for D arrays, associative arrays,
and delegates"
To: "robert at octarineparrot.com" <robert at octarineparrot.com>


Robert,

I'm a member of the DWARF committee.  In our last meeting, I was assigned
the task of understanding your proposal and helping to turn it into a
formal proposal (with page reference, edit directions and the final formal
text).

If you don't mind, I'd like to know a bit more about the background of the
proposal.

For example, are you working with a compiler, a debugger or both?  Are
these concepts core features of D or standard user features (e.g., are they
like Fortran COMMON, which is a core feature with important semantics or
like Pascal WITH, which is a notational convenience)?  Are these D features
primitives (like C++'s "bool") or the result of composition (like "const
long long int")?

As I understand your suggestion, I think it's possible to get the same
effect with a smaller change to DWARF.  For example we could add a new
attribute and define dynamic array types this way:

DW_TAG_structure_type                         // A structure
 DW_AT_D_language_dynamic_array_descriptor   // Attribute tells consumer
what this is
 DW_AT_name [pointer to "darray"]
 [specification of an size_t named "length"}
 [specification of a T* pointer named "ptr"]

In other words, as though it were this C code but with the D-language flag
added and something useful where I have "...":

   typedef ... T;

   typedef struct darray_struct {
       size_t  length;
       T      *ptr;
   } darray;

Similarly we could add DW_AT_D_language_associative_array and
DW_A_D_language_delegate to standard structure definitions.

Would this simpler proposal work as well for your purposes?

Thanks for any help you can give me,

       -John
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