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Re: [Dwarf-Discuss] Some DWARFv5 draft feedback
- From: Michael Eager <eager at eagercon dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Thu, 01 Dec 2016 11:32:05 -0800
- Subject: Re: [Dwarf-Discuss] Some DWARFv5 draft feedback
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(a)eagercon.com
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