>> I think the original intent of this wording was to describe the bit >> offset of a field within a structure, given the byte address of the >> beginning of the structure. Said bit offset would be the total number >> of bits occupied by preceding fields plus internal padding, as >> demonstrated in the big- and little-endian examples in D.2.8. We >> should never have implied that this bit numbering was meant to match >> the bit numbering convention used in the ABI specification. > > Unfortunately, that's exactly what DWARF says.
But it's not what we meant, and we should fix it. >> This is not the only place we use this bit numbering convention -- we >> also use it for the DW_AT_data_bit_offset attribute, and it's defined >> in Section 5.7, with a reference to the examples in D.2.8. > > Also, not what we want. Why is this not what we want? There's really no better way to define a field's position within a structure. >> I think it's also unfortunate that we allowed the offset field for >> DW_OP_bit_piece to apply to register values. That's a very different >> use for the value, and just adds to the confusion. > > It's the same use when a register contains multiple fields of a struct. How about if we define this in terms of a left shift instead of a bit offset relative to the least-significant bit? "If the location is a register, the value is shifted left by offset bits within the register." -cary _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
