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;

Sorry, that should be:

  var off = SELF'offset + 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.