Merge branch 'bpf-arm64-__arena-kfunc-and-struct_ops-arguments'

Puranjay Mohan says:

====================
bpf, arm64: __arena kfunc and struct_ops arguments

The x86-64 JIT recently gained support for the __arena and
__arena__nullable argument suffixes on kfuncs and struct_ops stubs. This
adds the arm64 side and flips bpf_jit_supports_arena_args() on, so the
verifier stops rejecting these programs on arm64.

Patch 1 is an independent fix. save_args() reads stack-passed arguments
at FP + 32, which only holds when the trampoline is entered through the
fentry call and two frame records are pushed. A struct_ops trampoline is
entered via blr and pushes one frame fewer, so its stack arguments start
at FP + 16 and every one of them was read two slots off. No struct_ops
member passed arguments on the stack until the test added by commit
2d4de9a493a0, which is why this went unnoticed. It carries a Fixes tag
and can be taken separately; note that the test covering it only runs on
arm64 once the rest of this series lands.

Patch 2 adds an ADD/SUB (extended register) encoder to the insn library,
so the JIT can zero-extend and add in one instruction.

Patches 3 and 4 are the JIT work. A kfunc argument is rebased onto the
arena base at the call site:

        add     xN, x28, wN, uxtw

and a nullable one skips the add so NULL stays NULL:

        mov     wN, wN
        cbz     wN, 1f
        add     xN, x28, wN, uxtw
1:

A struct_ops callback converts in the other direction, in the trampoline
while saving arguments into the BPF ctx, with the low half of the arena
base kept in x11:

        sub     w10, wsrc, w11
        str     x10, [sp, #slot]

Patches 5 and 6 add arm64 JIT-sequence assertions and drop the x86-64
gating from the existing arena argument tests. Patch 7 is arch-neutral:
it adds a struct_ops member whose first argument is a 16-byte struct
passed by value, so the arena pointer does not land at the ctx slot its
argument index suggests. Nothing covered that before, and it is the case
patch 4 has to get right.

Changelog:
V1: https://lore.kernel.org/bpf/20260810190922.3408757-1-puranjay@kernel.org/
Changes in v2:
- patch 2: fix the decode masks for the new extended-register predicates,
  0x7F200000 -> 0x7FE00000. opt in bits 23:22 is part of the opcode here
  rather than a shift type, and any value other than 00 is unallocated
  (Xu Kuohai). Also noted in the commit message. No functional change: the
  masks only feed aarch64_insn_is_*_ext(), which has no in-tree callers,
  while the encoder uses aarch64_insn_get_*_ext_value().
- patch 4: comment why the conversion in the stack-argument loop is not
  guarded by for_call_origin (Xu Kuohai).
- collect Reviewed-by/Acked-by from Xu Kuohai.
- rebase onto current bpf-next.
====================

Link: https://patch.msgid.link/20260813190356.335181-1-puranjay@kernel.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

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