lib/systems: Adjust stdenv.*Platform.rust.rustcTargetSpec for ELFv2 glibc

[OPNA2608]

Rustc 1.98 added official support for powerpc64-unknown-linux-gnuabielfv2! They just name it not quite that: https://doc.rust-lang.org/nightly/rustc/platform-support/powerpc64-unknown-linux-gnuelfv2.html

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Fixes i.e. pkgsCross.ppc64-elfv2.fd.

I don't know if this has come up in your cross ppc64-elfv2 deployments for work, but CC @minijackson just in case.

puna@Yubel ~/D/nixpkgs (wip/ppc64-installer-testing)> file /nix/store/pvsmsnp5ghwvv6mfcac5lcmakk5wqnrq-fd-powerpc64-unknown-linux-gnuabielfv1-10.5.0/bin/fd
/nix/store/pvsmsnp5ghwvv6mfcac5lcmakk5wqnrq-fd-powerpc64-unknown-linux-gnuabielfv1-10.5.0/bin/fd: ELF 64-bit MSB pie executable, 64-bit PowerPC or cisco 7500, Power ELF V1 ABI, version 1 (SYSV), dynamically linked, interpreter /nix/store/1jc1lk03jpvx5vlf25vvblvr56s1zbmm-glibc-powerpc64-unknown-linux-gnuabielfv1-2.42-84/lib/ld64.so.1, for GNU/Linux 3.10.0, not stripped
puna@Yubel ~/D/nixpkgs (wip/ppc64-installer-testing)> file /nix/store/6mr32jpr2s8a7g2c9hhvpvq6p7951ix6-fd-powerpc64-unknown-linux-gnuabielfv2-10.5.0/bin/fd
/nix/store/6mr32jpr2s8a7g2c9hhvpvq6p7951ix6-fd-powerpc64-unknown-linux-gnuabielfv2-10.5.0/bin/fd: ELF 64-bit MSB pie executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), dynamically linked, interpreter /nix/store/78lvs5hjgsx0hh0gv42p93v5xrim2n00-glibc-powerpc64-unknown-linux-gnuabielfv2-2.42-84/lib/ld64.so.2, for GNU/Linux 3.10.0, not stripped
puna@Yubel ~/D/nixpkgs (wip/ppc64-installer-testing)> file /nix/store/rjh7dpvaxanfpkb3h6xcv5d4n8wx31b3-fd-powerpc64-unknown-linux-musl-10.5.0/bin/fd
/nix/store/rjh7dpvaxanfpkb3h6xcv5d4n8wx31b3-fd-powerpc64-unknown-linux-musl-10.5.0/bin/fd: ELF 64-bit MSB pie executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), dynamically linked, interpreter /nix/store/zjrl0qa65qly3mb1jpi2k8w01bv5hq34-musl-powerpc64-unknown-linux-musl-1.2.6/lib/ld-musl-powerpc64.so.1, not stripped
puna@Yubel ~/D/nixpkgs (wip/ppc64-installer-testing)> /nix/store/pvsmsnp5ghwvv6mfcac5lcmakk5wqnrq-fd-powerpc64-unknown-linux-gnuabielfv1-10.5.0/bin/fd 'lomiri\.nix' nixos/tests/
nixos/tests/lomiri.nix
puna@Yubel ~/D/nixpkgs (wip/ppc64-installer-testing)> /nix/store/6mr32jpr2s8a7g2c9hhvpvq6p7951ix6-fd-powerpc64-unknown-linux-gnuabielfv2-10.5.0/bin/fd 'lomiri\.nix' nixos/tests/
nixos/tests/lomiri.nix
puna@Yubel ~/D/nixpkgs (wip/ppc64-installer-testing)> /nix/store/rjh7dpvaxanfpkb3h6xcv5d4n8wx31b3-fd-powerpc64-unknown-linux-musl-10.5.0/bin/fd 'lomiri\.nix' nixos/tests/
nixos/tests/lomiri.nix

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • powerpc64-linux (pkgsCross.ppc64-elfv1.fd, pkgsCross.ppc64-elfv2.fd, pkgsCross.ppc64-musl.fd)
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.
• Follows the automation/AI policy.

[emilazy]

Rust supports JSON target spec files for unsupported platforms, which would be the correct thing to use here; cc @dramforever.

[dramforever]

I'll rebase I have rebased #446668 some time later this week. PTAL

I think this is the nicest way to get custom target JSON working - although having target JSON files in-tree doesn't look particularly nice, I'm hoping that at least it could be temporary, until maaaybe upstream rustc adds a elfv2 variant.

[OPNA2608]

Changed this to instead add rustcTargetSpec settings for the ppc64-elfv1 & ppc64-elfv2 examples, and added a JSON spec file for the ELFv2 target generated with the help of Rust 1.94.0 on staging (hence still the staging target).

Do we have anything in /pkgs/top-level/release-cross.nix that actually checks Rust cross, so there's some automated tests of such target specs? Would it make sense to add one (i.e. fd)? Rust docs say that the JSON's format isn't stable and should be pinned to a compiler version, so it'd be nice to have some test of this.

[alyssais]

This will sadly be broken by #510674, which deprecates JSON target specs :(

[OPNA2608]

Hmm… So back to patching /compiler/rustc_target/src/spec/targets/powerpc64_unknown_linux_gnu.rs then, like in fbac021?

[alyssais]

I don't know what the right thing is now. :( They were asking for feedback on the target mechanism I think, so would be good to engage with that.

[OPNA2608]

Based on the conversations in rust-lang/rust#151528, rust-lang/rust#155620, and LibreELEC/LibreELEC.tv#11205, I guess this should go back to making changes in /compiler/rustc_target/src/spec/targets/ for now.

I couldn't find an example of how to i.e. make a powerpc64-unknown-linux-gnuabielfv2.rs that inherits the base settings from powerpc64-unknown-linux-gnu.rs, and I didn't plan on learning Rust just to fix a target that I realistically won't even use due to other issues, so I'd change this PR back to ~ the state of fbac021 if that's fine with everyone?

[alyssais]

If you're not otherwise going to use it, does making any change here justify the complexity increase in our rustc packaging? I'm all for supporting exotic platforms, but it seems silly to go out of our way to support something upstream doesn't, and that is also not useful for other reasons.

[OPNA2608]

I know we have users of powerpc64-unknown-linux-gnuabielfv2 (#451088 (comment), CC @minijackson), and people who IIRC would prolly prefer for us to have gnuabielfv2 as our default ABI again (CC @amaanq). I'm fine with ELFv1 myself, but I can test ELFv2 stuff on hardware, so I don't mind doing a little bit of work to support it.

[OPNA2608]

Should maybe be possible to just change the target adjustment in /lib/systems/default.nix soon: rust-lang/rust#144220

[OPNA2608]

Switched to adjusting our rustcTargetSpec to map GCC powerpc64-unknown-linux-gnuabielfv2 target -> rustc 1.98's new powerpc64-unknown-linux-gnuelfv2 target.