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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Aug 07, 2026 at 07:34:10PM +0200, Miguel Ojeda wrote:
> On Fri, Aug 7, 2026 at 2:43 PM Arnaldo Carvalho de Melo <acme@kernel.org> 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?

Can you think about one such niche case that is present in the kernel
rust .o files right now? I tried finding the `Option<NonZero<u32>>` to
look at its DWARF but couldn't find one.

- Arnaldo