Comment 7 for bug 2005122

[Backport]

The backport status for Bionic (18.04), Focal (20.04), Jammy (22.04), and Kinetic (22.10):

Bionic: https://git.launchpad.net/~canonical-foundations/ubuntu/+source/rustc/log/?h=bionic-1.66
Focal: https://git.launchpad.net/~canonical-foundations/ubuntu/+source/rustc/log/?h=focal-1.66
Jammy: https://git.launchpad.net/~canonical-foundations/ubuntu/+source/rustc/log/?h=jammy-1.66
Kinetic: https://git.launchpad.net/~canonical-foundations/ubuntu/+source/rustc/log/?h=kinetic-1.66

Notable differences from the mainline edition (Lunar):

* [Kinetic and Bionic only] Bundled LLVM 15.0.7 C/C++ sources
* [Except Kinetic] Removed dh-cargo requirements
* [Bionic only] Disabled outline LSE assembly helper requirements on aarch64

Known Issues:

* LLVM version on JJ and KK currently contains a bug that affects ppc64el where LLVM will encounter an address boundary error (segmentation fault) during bytecode emission. Upgrading the system LLVM to 15.0.7 is pending.
* Due to aging GCC runtimes in 18.04, out-of-line LSE helpers are unsupported on aarch64, while Rust requires this target feature to be enabled. A patch has been added to address this situation. As a result, all the LSE intrinsic functions will be emitted inline instead—impact: slightly worse atomic operation performance and larger binary size.

PPA preparation:

https://launchpad.net/~liushuyu-011/+archive/ubuntu/rust-updates-1.66/+packages

* Note:
Focal was uploaded as EVR 1.66.1+dfsg0ubuntu1~llvm2-0ubuntu0.20.04 in the PPA.
Bionic was uploaded as EVR 1.66.1+dfsg0ubuntu1~llvm2-0ubuntu0.18.04.5 in the PPA.
... despite the EVR should be 1.66.1+dfsg0ubuntu1~llvm-0ubuntu0.20.04 and 1.66.1+dfsg0ubuntu1~llvm-0ubuntu0.18.04, respectively.