[Dwarf-Discuss] Some DWARFv5 draft feedback
eager at eagercon.com
Thu Dec 1 11:32:05 PST 2016
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.
> 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:
> * 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?
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Michael Eager eager at eagercon.com
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