On Tue, Jul 9, 2024 at 2:09 PM Peter Maydell <peter.mayd...@linaro.org> wrote: > * what is the actual baseline requirement? We definitely want > to support "using rustup on an older system" (should be no > problem) and "current distro building QEMU using the distro's > rust", I assume. It would certainly be nice to have "building > QEMU on the older-but-still-in-our-support-list distro releases > with that distro's rust", but this probably implies not just > a minimum rust version but also a limited set of crates.
I don't think limiting ourselves to the set of crates in the distro is feasible. It's not the way the language works, for example I tried checking if the "cstr" crate exists and I didn't find it in Debian. We can define a known-good set of versions: * either via Cargo.lock (i.e. recording the versions and downloading them) or by including sources in the tree * at any time in qemu.git, at branching time (three times a year), or on every release (That's six possibilities overall). > I think (but forget the details) that some of what we've done > with Python where we accept that the older-but-still-supported > distro will end up taking the "download at build time" path > in the build system might apply also for Rust. Yes, and --without-download may be changed to the "--frozen" flag of cargo. > * what, on the Rust side, is the version requirement? Presumably > there's some features that are pretty much "we really need > this and can't do without it" and some which are "this would > be pretty awkward not to have but if we have to we can implement > some kind of fallback/alternative with a TODO note to come > back and clean up when our baseline moves forwards". Here are the stopping points that I found over the last couple weeks: 1.56.0: 2021 edition 1.59.0: const CStr::from_bytes_with_nul_unchecked (needed by cstr crate, see below) 1.64.0: std::ffi::c_char 1.65.0: Generic Associated Types 1.74.0: Clippy can be configured in Cargo.toml 1.77.0: C string literals, offset_of! I think 1.59.0 is pretty much the lower bound. Not having offset_of! will be a bit painful, but it can be worked around (and pretty much has to be, because 1.77.0 is really new). As far as I understand, Debian bullseye has 1.63.0 these days and it's the oldest platform we have. Paolo > At that point we have more information to figure out what > if any tradeoff we want to make. > > thanks > -- PMM >
