Fix powerpc64 big-endian FreeBSD ABI

[taiki-e]

Note that FreeBSD version bump may be reverted due to #120869 (comment). We may want to wait to merge this until that discussion is complete.

Fixes #120869 (comment)

PPC64 FreeBSD (ELFv1 and ELFv2, version 13.2)

It seems odd that ELFv1 and 13.N coexist.

https://www.freebsd.org/releases/13.0R/relnotes/

powerpc64 switched to ELFv2 ABI at the same time it switched to LLVM. This brings us to a parity with modern Linux distributions. This also makes the binaries from previous FreeBSD versions incompatible with 13.0-RELEASE. Kernel still supports ELFv1, so jails and chroots using older FreeBSD versions are still compatible. e4399d169acc

Well, it is also odd that this target claims ELFv2 support since our ABI code does not use ELFv2 on this target.

rust/compiler/rustc_target/src/callconv/powerpc64.rs

Lines 102 to 111 in be01dab

	let abi = if cx.target_spec().env == "musl" {
	ELFv2
	} else if cx.target_spec().os == "aix" {
	AIX
	} else {
	match cx.data_layout().endian {
	Endian::Big => ELFv1,
	Endian::Little => ELFv2,
	}
	};

@rustbot label +O-PowerPC +O-freebsd

[rustbot]

r? @pnkfelix

rustbot has assigned @pnkfelix.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

[beetrees]

FreeBSD ports already carries a patch with this effect, so this PR will make upstream Rust match what FreeBSD ports already does.

cc target maintainers from #129220: @asomers @MikaelUrankar

[adalava]

@taiki-e I can confirm that FreeBSD 13 (and also 14) powerpc64 (big-endian) kernel is compatible with both ELFv1 and ELFv2 and there's no plans to deprecate ELFv1 compatibility in the kernel at this moment. Users running 13/14 can jail or chroot to a sysroot from 12.x or 11.x to run their stuff. The package build servers (ports) generally uses the most recent kernel version and is able to build packages for FreeBSD 12/13/14 inside a Jail.

FreeBSD 12 is EOL since Dec/2023 so the project doesn't release ELFv1 binaries since then (sysroot, kernel and ports/packages). In case of Rust, I think it's up to Rust developers if it's too soon or not to deprecate ELFv1 now. We recommend users to upgrade but Rust may want keep supporting ELFv1 users for a while.

If you decide to keep both, I'd recommend decide the ABI based on OS major version retrieved from compiler's target triple: "powerpc64-unknown-freebsd12", "powerpc64-unknown-freebsd13", for instance, so ELFv1 if OS version <13 and ELFv2 by default. For the powerpc64le (little-endian) target it must be ELFv2 only.

This is how LLVM choose the ABI: llvm/llvm-project@8edf759#diff-bac41c71569f27df21a843bcd74d2e604ed508afbdf141777761dfb545c5d228R1919

[taiki-e]

@adalava We have decided to drop FreeBSD 12 support as discussed in the PR I linked to (#120869). That PR itself was reverted (#132228) due to another issue (#132185), but the decision itself there has not been reversed (#132228 (comment)).

[pnkfelix]

@bors r+

[bors]

@pnkfelix: 🔑 Insufficient privileges: Not in reviewers

[pnkfelix]

@pnkfelix: 🔑 Insufficient privileges: Not in reviewers

ha ha okay yeah I figured that might happen

[pnkfelix]

r? @rust-lang/compiler

[apiraino]

@bors r+

[bors]

📌 Commit fabf652 has been approved by apiraino

It is now in the queue for this repository.

[apiraino]

@bors r=pnkfelix

[bors]

💡 This pull request was already approved, no need to approve it again.

• There's another pull request that is currently being tested, blocking this pull request: add some debug-assertion crash tests #132789

[bors]

📌 Commit fabf652 has been approved by pnkfelix

It is now in the queue for this repository.

[apiraino]

@taiki-e when you have a chance, can you please rebase? this is good to go. thanks!

[compiler-errors]

@apiraino: it's already approved though?

[taiki-e]

@apiraino Rebased.

[compiler-errors]

@bors r=pnkfelix