Andreas --

Please submit comments about the Public Draft at

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
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