Re: [PATCH proxmox v2 02/10] proxmox-alloc: document undefined behavior regarding custom allocs

["Max R. Carrara" <m.carrara@proxmox.com>]

On Wed Sep 2, 2026 at 6:14 PM CEST, Robert Obkircher wrote:
> > Add a new example at examples/ub.rs with tests that demonstrate
> > incorrect usage & undefined behavior of custom allocations.
>
> I don't think that it is a good idea to include a runnable example,
> because it can theoretically format your hard drive, and it will likely
> result in false positives from vulnerability scanners.

Hmm, good point, I'll include reworked examples in the docs in v2, and
mark them with `no_run`, since it's suggested to use this for
documenting UB [no_run].

Thanks!

>
> These examples also conflate allocation of DSTs and over-alignment to a
> runtime value, which are completely separate concepts that can be
> understood separately.

Fair, I'll try to separate the two. Thanks!

[no_run]: https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html#no_run

>
> >
> > Add a hint in the `aware_boxed` module's docs that such an example
> > exists in the crate.
> >
> > Signed-off-by: Max R. Carrara <m.carrara@proxmox.com>
> >
> > diff --git a/proxmox-alloc/Cargo.toml b/proxmox-alloc/Cargo.toml
> > index 4eeeb787..b16496f6 100644
> > --- a/proxmox-alloc/Cargo.toml
> > +++ b/proxmox-alloc/Cargo.toml
> > @@ -11,6 +11,10 @@ repository.workspace = true
> >  license.workspace = true
> >  exclude.workspace = true
> >
> > +[[example]]
> > +crate-type = ["staticlib"]
> > +name = "ub"
> > +
> >  [dependencies]
> >
> >  [dev-dependencies]
> > diff --git a/proxmox-alloc/examples/ub.rs b/proxmox-alloc/examples/ub.rs
> > new file mode 100644
> > index 00000000..aa97b02b
> > --- /dev/null
> > +++ b/proxmox-alloc/examples/ub.rs
> > @@ -0,0 +1,99 @@
> > +//! This example contains various tests that demonstrate [undefined behavior].
> > +//! Needless to say, you should not use what's shown here in your own code.
> > +//!
> > +//! You can run this example's tests using the following command:
> > +//!
> > +//! ```text
> > +//! cargo test --package proxmox-alloc --example ub
> > +//! ```
> > +//!
> > +//! Alternatively, if you want to see what kinds of [undefined behavior] get
> > +//! caught by [Miri], use the following instead:
> > +//!
> > +//! ```text
> > +//! cargo +nightly miri nextest run --package proxmox-alloc --example ub
> > +//! ```
> > +//!
> > +//! Note that this requires [`cargo nextest`][nextest] to be installed on your
> > +//! nightly toolchain. This will guarantee that all tests are run, even if they
> > +//! fail (which they do when you use Miri).
> > +//!
> > +//! [Miri]: https://github.com/rust-lang/miri
> > +//! [nextest]: https://nexte.st/
> > +//! [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
> > +
> > +#[cfg(test)]
>
> This could be `#[cfg(all(test, miri))]`, but even then I don't think
> miri supports something like #[should_panic] but for expected UB.