Re: Linux kernel in-tree Rust support

[Adrian Bunk]

On Sun, Jul 12, 2020 at 12:39:44PM -0700, Josh Triplett wrote:
> On Sun, Jul 12, 2020 at 03:31:51PM +0300, Adrian Bunk wrote:
> > On Thu, Jul 09, 2020 at 11:41:47AM -0700, Nick Desaulniers wrote:
> > >...
> > > but also a larger question of "should we do
> > > this?" or "how might we place limits on where this can be used?"
> > >...
> > 
> > I won't attend, but I do have a topic that should be covered:
> > 
> > Firefox always depends on recent Rust, which forces distributions to 
> > update Rust in stable releases.
> > 
> > As an example:
> > Ubuntu LTS releases upgrade to a new Rust version every 1-2 months.
> > Ubuntu 16.04 started with Rust 1.7.0 and is now at Rust 1.41.0.
> > 
> > It would not sound good to me if security updates of distribution
> > kernels might additionally end up using a different version of the
> > Rust compiler - the toolchain for the kernel should be stable.
> > 
> > Would Rust usage in the kernel require distributions to ship
> > a "Rust for Firefox" and a "Rust for the kernel"?
> 
> Rust has hard stability guarantees when upgrading from one stable
> version to the next. If code compiles with a given stable version of
> Rust, it'll compile with a newer stable version of Rust. Given that, a
> stable distribution will just need a single sufficiently up-to-date Rust
> that meets the minimum version requirements of both Firefox and Linux.
>...

API stability avoids problems that are visible early as build errors.

Rust cannot offer a hard stability guarantee that there will never be 
a code generation regression on any platform.

Rust gets updated frequently.
Sometimes this also changes the LLVM version used by Rust.
Debian stable supports targets like ARMv5 and 32bit MIPS.
Distribution kernel updates are often automatically installed
on user hardware.

cu
Adrian