Re: [PATCH bpf-next v7 08/10] selftests/bpf: Add C tests for 16-byte returns in R0:R2

[Yonghong Song <yonghong.song@linux.dev>]

On 8/18/26 11:49 PM, bot+bpf-ci@kernel.org wrote:
>> Add selftests that exercise a 16-byte return value passed in the R0:R2
>> register pair, written in C so that they depend on the compiler lowering
>> the register-pair return.
>>
>> The R0:R2 convention is only emitted by LLVM 23 and newer, and a by-value
>> aggregate return does not compile at all before that, so the programs sit
>> behind a __clang_major__ guard. An older compiler builds the dummy test in
>> the #else branch instead, which keeps the object non-empty and says in its
>> description why nothing was exercised.
>>
>> The kfunc tests are tagged __arch_x86_64/__arch_arm64 and skip elsewhere.
>> Those are the architectures whose JIT advertises
>> bpf_jit_supports_kfunc_ret_reg_pair(), which bpf_add_kfunc_call() requires
>> before it accepts a kfunc returning more than 8 bytes, and they are also
>> the only ones building the kfuncs.
> The changelog states that x86_64 and arm64 are "the architectures whose
> JIT advertises bpf_jit_supports_kfunc_ret_reg_pair()". Is this accurate?
>
> Looking at commit 4b4530101f35 ("bpf: Wire up JIT support for 16-byte
> kfunc returns"), the first patch of this same series, it adds
> bpf_jit_supports_kfunc_ret_reg_pair() returning true to three JITs, not
> two:
>
>    arch/x86/net/bpf_jit_comp.c       bool bpf_jit_supports_kfunc_ret_reg_pair(void) { return true; }
>    arch/arm64/net/bpf_jit_comp.c     bool bpf_jit_supports_kfunc_ret_reg_pair(void) { return true; }
>    arch/riscv/net/bpf_jit_comp64.c   bool bpf_jit_supports_kfunc_ret_reg_pair(void) { return true; }
>
> and its own changelog says so explicitly: "Only the x86-64, arm64 and
> riscv64 JITs opt in so far." kernel/bpf/core.c keeps the __weak default
> at false for everything else.
>
> Stating the JIT capability as the reason for the architecture tagging
> misleads a reader into believing riscv64 has no R0:R2 JIT support,
> which is the opposite of what the series does.

We are fine. I didn't add riscv64 selftest. As mentioned in
    bpf: Wire up JIT support for 16-byte kfunc returns
riscv64 is not tested.

>
>
> ---
> AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
> See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md
>
> CI run summary: https://github.com/kernel-patches/bpf/actions/runs/32221968339