Re: [PATCHES 00/12] pahole: Support more rust tags and references to dwz alternate debug files

On Fri, Aug 7, 2026 at 2:43 PM Arnaldo Carvalho de Melo <[email protected]> wrote:
>
> Adding Miguel to the CC list, Miguel we're trying to improve BTF support
> for Rust, this series handles multiple enabling fixes/improvements that
> gets us to the next level, i.e. we can load everything from DWARF, now

Thanks for the Cc! Cc'ing rust-for-linux and Gary.

> its time to try to map it to existing BTF kinds and propose BTF
> extensions when we can't use existing encodings.

Sounds cool :)

> Inferring from "does any member have a niche layout" means
> reverse-engineering rustc's layout algorithm, which is explicitly
> unstable and unspecified. It'd break silently on a compiler bump, with
> no way to tell from the DWARF that you got it wrong.

Yeah, the LLM is correct here: the Rust compiler gives very few
guarantees for the default `repr`, i.e. in common cases it has the
freedom to use whatever layout it wants (i.e. even for essentially
equivalent types in the same compilation unit) -- the official docs
are at:

  https://doc.rust-lang.org/reference/type-layout.html

>     u8                  __discriminant;      /*  0  1 */

For the niche cases like `Option<NonZero<u32>>`, what would be printed?

Cheers,
Miguel