[Dwarf-discuss] bit-string

[pogo 59]

My first thought would be that DW_TAG_string_type with a one-bit base type,
but it's not clear that the other attributes would be interpreted in a way
that correctly navigated the bit string. You could try using
DW_TAG_packed_type pointing to a DW_TAG_string_type, in the hopes that
consumers would figure out that it was a "packed" string of bits, and that
the element stride and sizes should be bits. I believe Pascal would
describe "packed array of boolean" that way, or however Pascal spells that
type.

If that doesn't pan out, DW_TAG_array_type can certainly describe bit-sized
elements, with DW_AT_bit_stride of 1. This might not get you string-like
semantics in the consumer, but it would describe the data accurately.
--paulr

On Wed, Dec 18, 2024 at 8:50 AM Thomas David Rivers via Dwarf-discuss <
dwarf-discuss@lists.dwarfstd.org> wrote:

>
> PL/I has the concept of a "string", which can be a fixed-length
> (possibly not known at compile time), or a fixed size with a 4-byte or
> 2-byte
> runtime length prefix, or, depending on the consituents, a NULL (zero-byte)
> terminated string.
>
> For "character-like" strings, the constituents can be 1-byte, 2-byte,
> 4-byte strings, or UTF-8 values.  (e.g. strings of characters, or strings
> of UTF-8 values, or strings of 4-byte unicode values.)
>
> All of these seem to be straightforwardly handled by DWARF-5.
>
> However, PL/I also has a "BIT string", which is a left-adjusted string
> of bits, either of a fixed length (# of bits) or of a fixed size
> with a either a 2-byte or 4-byte length prefix. Of course, there isn't
> a NULL-terminated variant of this string, because a zero-bit is part of
> the data.  The sizes may not be known at compile time.
>
> I've gone thru the DWARF-5 standard a few times, but can't seem to
> envision a straight-forward way to represent this.
>
> Furthermore, an un-prefixed bit-string doesn't necessarily begin
> on a byte boundary, and, depending on the environment, needs to
> be represented as a bit-offset which may be composed (even at runtime)
> of (byte-location + bit-offset-in-byte).
>
> Any suggestions on how to represent this in DWARF (5 or later) would
> be appreciated!   Perhaps it's just something obvious I'm overlooking??
>
>         - Many Thanks! -
>         - Dave Rivers
>
> --
> rivers@dignus.com
> --
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>
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