On Thu, Jan 26 2017, Michael Eager wrote: > I don't understand the assertion that "most significant" can not be > applied to registers. In the case where a register contains a single > value, this appears to be unambiguous. When a register contains > multiple values (some architectures support 2 16-bit values in a > 32-bit register, for example), then additional clarification may be > needed. The ABI provides this, usually. The situation where a single > value is split across two registers is similar. When discussing > compound values (such as floating point) it is common to say that the > sign bit is in the most-significant bit of the register, without > ambiguity.
Hm, can you point to a formal definition? The usual definition of "most/least significant bit" assumes that the underlying object is a single binary integer: https://en.wikipedia.org/wiki/Least_significant_bit And I see how all this still makes sense for registers that can "naturally" contain full-sized integers. But not in general. You already list some cases that aren't that obvious, and there are many more. When you say "the ABI provides this [clarification], usually", where did you see that? For instance, when looking at the System V Application Binary Interface AMD64 Architecture Processor Supplement Draft Version 0.99.7, I don't see any definition related to DWARF pieces, nor a clarification of the terms "most/least signficant bit" of a register. Did you see something like that in any other ABI? Maybe I'm too picky, but IMO a standard document should rely on formally defined terms only. And "least significant bit", when applied to a register, is not one of those, I think. -- Andreas _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
