Re: DWARF5 line number program header

[Jose E. Marchesi]

Hi Martin.

>>  40     file_name_entry_format_t[file_name_entry_format_count] 
>> file_name_entry_format; // offset: 39, size: 4
>>  41     // DW_LNCT_path = 0x1
>>  42     // DW_FORM_line_strp = 0x1f
>>  43     // DW_LNCT_directory_index  = 0x2
>>  44     // DW_FORM_udata  = 0x0f
>>  45     ULEB128 file_names_count; // offset: 43, size: 1 value: 2
>>  46     uint<32> FILES;

If I understood properly, you basically have an array of format
descriptors, each descriptor determining the shape of each element in a
sequence of elements that follow the array.  Schematically:

type Challenge =
  struct
  {
    ElemForm[NELEM] forms;
    Elem elem0; /* Shape determined by forms[0] */
    Elem elem1; /* Shape determined by forms[1] */
    ...
    Elem elemM; /* Shape determined by forms[NELEM-1] */
  };

One possibility would be to define a computed field whose getter does it
imperative style, like:

type Elem =
  struct
  {
    int<32> type;
    union
    {
      Path path;
      DirectoryIndex dirindex;
    } value;
  };

type ConformedElements =
  struct
  {
    ElemForm[NELEM] forms;

    var begin_elems = OFFSET;
    computed Elem[] elems;
    method get_elems = Elem[]:
    {
      var elems = Elem[]();
      var off = begin_elems;

      for (form in forms)
      {
        var elem = Elem {};

        if (form is a path)
           elem = Elem { type = PATH, value.path = Path @ off };
        else if (form is a directory index)
           elem = Elem { type = DIRINFO, value.dirinfo = DirInfo @ off };
        else
          ...

        apush (elems, elem);
        off += elem'size;
      }
      return elems;
    }
  };

Seems to me that this is a more elaborated example of the sparse table
idiom described in this pokology article:

https://jemarch.net/pokology-20230128.html

Note that the `elems' computed field, which is an array, is not mapped
itself.  But each elems[N].data.WHATEVER are mapped.

Hope this is helpful.