zfs(openzfs): enable OpenZFS on aarch64 (follow-on to #1423)

[gburd]

Enables the vendored OpenZFS 2.4.3 port (added in #1423) to build on aarch64, with x86_64 left byte-for-byte unchanged.

Depends on: #1423

This is the aarch64 follow-on to #1423 ("zfs: selectable in-kernel ZFS (BSD or OpenZFS 2.4.2) via upstream submodule + patch series"). It is cut directly on top of that PR's tip and must land after it — the two commits here only make sense against the modules/open_zfs/ submodule + patch-series layout introduced by #1423.

What this does

Two small, self-contained changes — the aarch64-enablement nugget re-authored against the current modules/open_zfs/ layout:

1. modules/open_zfs/patches/0031-*.patch — SPL sha512 stub / SIMD fallback.
   The OSv SPL layer (patch 0001) only recognized x86_64: isa_defs.h #errored on any other ISA, and simd.h's non-x86 feature-detection stub block was missing zfs_sha512_available(). On x86_64 SHA-512 availability comes from the sha512-x86_64.S asm path so the stub was never needed; aarch64 has no such asm hook wired into the SPL, so icp/algs/sha2 calls zfs_sha512_available() and fails without the fallback. Patch 0031 adds an __aarch64__ ISA branch to isa_defs.h and the missing zfs_sha512_available() B_FALSE stub to simd.h. The submodule stays pinned to the pristine upstream zfs-2.4.3 tag — this is a new entry in the patch series, not a submodule re-pin.

2. modules/open_zfs/open_zfs_sources.mk — arch-conditional ICP asm object lists.
   The x86_64 ICP crypto asm objects (aes_amd64.S, aes_aesni.S, aeskey.c) have no top-level __x86_64__ guard and emit raw x86 instructions, so an aarch64 build's assembler chokes on them. (The raidz vdev_raidz_math_* objects already coexist across arches via per-file #ifdef guards; the ICP asm objects do not.) The object selection is now gated on $(arch): x64 gets aeskey.o + the four x86_64 asm objects exactly as before; aarch64 gets the #if defined(__aarch64__)-guarded ARMv8 sha256/sha512 asm and the native ARMv8 blake3 asm (all present in the upstream zfs-2.4.3 submodule). No Makefile change is needed — open_zfs_sources.mk is already included after arch is set.

x86_64 is unaffected (arch-gated)

With arch=x64 the emitted openzfs-icp / openzfs-icp-asm object lists are byte-identical to #1423 (verified by expanding both branches of the makefile). Patch 0031's hunks are all guarded by __aarch64__ or the existing non-x86 #else, so x86_64 preprocessor output is unchanged.

Not included

• No submodule re-pin (2.4.3 preserved).
• No libsolaris.so / userspace-CLI compile-flag changes. The old aarch64 branch bundled an -isystem→-I libspl include-ordering tweak with unrelated io_uring syscall aliases; that swap is not arch-gated, only manifests during an aarch64 userspace build, and risks perturbing the x86 userspace build if applied blind. It's deferred until it can be validated on real aarch64 hardware.

⚠️ BUILD-UNVERIFIED on aarch64 — needs an aarch64 metal build+boot to validate before un-drafting.

This was re-authored from the older aarch64 work by inspection against the current layout; it has not been compiled or booted on aarch64 (no aarch64 toolchain/hardware available at authoring time). The x86_64 no-op property is verified by makefile expansion, but the aarch64 build+boot path must be exercised on aarch64 hardware before this leaves draft.

[gburd]

Same status as #1423: this branch's base predates several merged tests and it needs the full forward-port + ZFS module restructure, not just a Makefile fixup. I will convert its ZFS test entries to standalone tests += lines (per #1469) as part of that forward-port. Holding until then.

[gburd]

#1423 merged, so this is rebased onto master. Most of the earlier ZFS content is now on master via the squash-merge, so this reduces to just the aarch64-specific enablement:

• aarch64: raise the ARM generic-timer frequency ceiling to 2GHz
• libc: gate the aarch64 atomic.h kernel-only includes so the ZFS userspace builds
• zfs(openzfs): make the ICP asm object lists arch-conditional for aarch64
• zfs(openzfs): enable aarch64 SPL isa_defs and the sha512 SIMD B_FALSE fallback

The post-restructure layout carries the OSv SPL platform files as parent-tracked source under modules/open_zfs/osv/ rather than as submodule patches, so the SPL isa_defs/simd change is applied there directly. The vnode_pager_setsize NULL-vnode guard from the old series is already on master, so it is dropped here.

x64 verify: conf_zfs=openzfs fs=zfs compiles and links clean (loader.elf, libsolaris.so, libzfs.so, zpool.so), no regression from the aarch64 SPL/simd edits.

aarch64 build-verify pending: the aarch64 cross-build compiles all of the changed SPL/ICP/atomic/timer objects clean, but the full openzfs image build is currently blocked on an unrelated pre-existing gap - the aarch64 userspace libzfs cannot find zlib.h in the cross toolchain include path. Leaving this draft until the aarch64 openzfs image is verified end to end.

[gburd]

aarch64 conf_zfs=openzfs builds clean (rc=0) on a native arm64 host: loader.elf, libsolaris.so, libzfs.so, libzfs_core.so, zpool.so, and zfs.so all compile and link with zero errors (301 OpenZFS objects), and the resulting aarch64 loader boots (banner + network up). The arch-conditional ICP asm selection resolves correctly: aarch64 pulls the ARMv8 sha256/sha512 and blake3 asm and none of the x86 objects, x86_64 is byte-identical to before.

The image build was verified on a native arm64 toolchain (gcc 13.3.1, binutils 2.40), matching the toolchain used to qualify the x86_64 OpenZFS image in #1423. Building natively sidesteps the earlier blocker: the aarch64 userspace libzfs could not find zlib.h in a cross toolchain. That was a cross-build include-path gap in the toolchain, not in this change; a native build finds the platform zlib headers and compiles cleanly, so no source change was needed for it.

One cleanup in this revision: the arm-clock.cc generic-timer comment is now fully vendor- and core-neutral (it explains only that current server ARM cores report frequencies above 1GHz, which the old 1GHz ceiling rejected; the ceiling is raised to 2GHz). The code is otherwise identical to the previous revision. The functional OpenZFS content is unchanged from #1423 (same submodule pin, same platform sources); this PR only adds the aarch64-specific SPL isa_defs, the SHA-512 SIMD C fallback, the userspace atomic.h gating, and the arch-conditional ICP asm lists. Ready for review.