Re: [PATCH bpf-next v6 09/10] selftests/bpf: Add inline-asm and subprog tests for R0:R2 returns

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

On 8/16/26 9:42 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The test `aggregate_ret_kfunc_too_big_fail` is incorrectly restricted to only run on x86_64 and arm64 architectures.
> --
>
> --- Patch [9]: [PATCH bpf-next v6 09/10] selftests/bpf: Add inline-asm and subprog tests for R0:R2 returns ---
> commit b44fbeb59afa99f6be0f33037220d124e0fb4e12
> Author: Yonghong Song <yonghong.song@linux.dev>
>
> selftests/bpf: Add inline-asm and subprog tests for R0:R2 returns
>
> This commit adds BPF inline-assembly tests to cover BPF-to-BPF returns, kfunc
> calls, backtracking, and liveness for functions returning values in the R0:R2
> register pair. It also includes an extension test to ensure a function returning
> R0:R2 cannot be replaced.
>
>> diff --git a/tools/testing/selftests/bpf/progs/aggregate_ret_kfunc.c b/tools/testing/selftests/bpf/progs/aggregate_ret_kfunc.c
>> new file mode 100644
>> index 0000000000000..c23b4beb1773c
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/aggregate_ret_kfunc.c
> [ ... ]
>
>> +/*
>> + * A return value larger than 16 bytes does not fit in R0:R2 and is rejected by
>> + * btf_distill_func_proto(), before the KF_FASTCALL and JIT-capability checks,
>> + * so this behaves the same on every architecture.
>> + */
>> +SEC("tc")
>> +__arch_x86_64 __arch_arm64
> [Severity: Medium]
> Are these architecture restriction tags intended here?
>
> The comment right above mentions that this test behaves the same on every
> architecture, but the __arch_x86_64 and __arch_arm64 tags artificially limit
> aggregate_ret_kfunc_too_big_fail() to only run on those two architectures,
> which prevents the test from running on others.

Okay, I don't have 100% confidence about every architecture. So let us
change to

/*
  * A return value larger than 16 bytes does not fit in R0:R2 and is rejected by
  * btf_distill_func_proto() before the KF_FASTCALL and JIT-capability checks.
  */

>
>> +__failure __msg("The function bpf_kfunc_call_test_ret_big return type STRUCT is unsupported")
>> +__naked int aggregate_ret_kfunc_too_big_fail(void)
>> +{
>> +	asm volatile (
>> +	"call %[bpf_kfunc_call_test_ret_big];"
>> +	"r0 = 0;"
>> +	"exit;"
>> +	:
>> +	: __imm(bpf_kfunc_call_test_ret_big)
>> +	: __clobber_all);
>> +}