[Dwarf-Discuss] DWARF piece questions

Andreas Arnez arnez at linux.vnet.ibm.com
Fri Dec 9 11:11:18 PST 2016


Although I've already created public comments for (most of) this,
Michael Eager suggested that I post my questions regarding DWARF pieces
on this list (again).

All of these questions are related to the definition of DW_OP_piece and
DW_OP_bit_piece:

* Is "DW_OP_piece(n)" equivalent to "DW_OP_bit_piece(8*n, 0)"?

* What is the correct placement rule for register pieces?  ABI-defined
  or lsb0-ordered?  If lsb0-ordered, how exactly is that order defined
  for non-integer registers?

* Shall DW_OP_bit_piece ignore the offset for stack- and implicit
  values?

* What is the "least significant bit" of an implicit value?  And is it
  intentional that the placement rule differs between implicit- and
  memory values?

* Some DWARF producers describe a register pair just with a single
  DW_OP_reg<n>.  Can a register piece reach into the next register like
  that as well?

* Is "DW_OP_reg*" followed by "DW_OP_piece(size of object type)" always
  equivalent to omitting the piece operation?

--
Andreas



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