[Dwarf-Discuss] Some DWARFv5 draft feedback

Michael Eager eager at eagercon.com
Thu Dec 1 11:32:05 PST 2016


Andreas --

Please submit comments about the Public Draft at http://dwarfstd.org/Comment.php.

On 12/01/2016 06:17 AM, Andreas Arnez wrote:
> On Thu, Dec 01 2016, Mark Wielaard wrote:
>
>> BTW. It would be handy if there were sources for the spec so one can
>> create patches for simple typos. Also it is somewhat opaque how Issues
>> are handled. Could they and any comments from the committee be sent to
>> the mailinglist to make tracking changes to the draft easier.
>
> +1.
>
>
> While we're at it, DWARF5 should improve the description of DW_OP_piece
> and DW_OP_bit_piece.  AFAIK, their handling is fairly broken in all
> existing DWARF producers and consumers (certainly in GDB -- in multiple
> ways!), so even incompatible changes may not cause much harm.  See my
> previous mails on this topic:
>
>   http://lists.dwarfstd.org/private.cgi/dwarf-discuss-dwarfstd.org/2016-March/004229.html
>   https://sourceware.org/ml/gdb/2016-01/msg00013.html
>
> E.g.:
>
> * DW_OP_bit_piece: [...] "If the location is a register, the offset is
>    from the least significant bit end of the register."
>
>    Is it intentional that this differs from the definition of
>    DW_OP_piece, where the "placement of the piece within that register is
>    defined by the ABI"?  Or can it be assumed (like all current
>    producers/consumers do, AFAIK) that DW_OP_piece shall behave as if it
>    was a DW_OP_bit_piece with offset 0?  What does the least significant
>    bit end even mean, say, for a vector register?  And is this really a
>    useful definition for FP registers, where the natural alignment is
>    from the *most* significant bit end?
>
> * DW_OP_piece: Some existing producers may emit DW_OP_piece operations
>    that exceed the size of a single register, supposedly referring to
>    multiple ("consecutive") registers.
>
>    This usage is not covered by the current description of DW_OP_piece.
>    Should it be?
>
> --
> Andreas
>
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-- 
Michael Eager	 eager at eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077


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