Re: [PATCH bpf-next v5 09/11] selftests/bpf: Add C tests for 16-byte returns in R0:R2

On 8/13/26 2:11 PM, [email protected] wrote:
>> diff --git a/tools/testing/selftests/bpf/progs/aggregate_ret_struct_c.c b/tools/testing/selftests/bpf/progs/aggregate_ret_struct_c.c
>> new file mode 100644
>> index 000000000000..83b1a3751988
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/aggregate_ret_struct_c.c
> [ ... ]
>
>> +struct pair {
>> +	__u64 hi;	/* R0 */
>> +	__u64 lo;	/* R2 */
>> +};
>> +
>> +union upair {
>> +	__u64 halves[2];
>> +	struct {
>> +		__u64 lo;	/* R0 */
>> +		__u64 hi;	/* R2 */
>> +	} parts;
>> +};
> This isn't a bug, but struct pair puts hi in R0 while union upair's
> parts puts lo in R0 - was the inverted naming in the union deliberate,
> or would matching the struct's order (or first/second) make the R0:R2
> mapping easier to follow?

Thanks. This is an oversight. Will fix 'struct pair' with proper ordering.

>
>> +
>> +static __noinline struct pair make_pair(__u64 a, __u64 b)
>> +{
>> +	struct pair p = { .hi = a + b, .lo = a - b };
>> +
>> +	return p;
>> +}
>> +
>> +SEC("tc")
>> +__load_if_JITed()
>> +__success __retval(0)
>> +int aggregate_ret_struct_c_test(struct __sk_buff *skb)
>> +{
>> +	__u64 a = skb->len ^ MIX_A;
>> +	__u64 b = skb->len ^ MIX_B;
>> +	struct pair p;
>> +
>> +	p = make_pair(a, b);
>> +	if (p.hi != a + b)
>> +		return 1;
>> +	if (p.lo != a - b)
>> +		return 2;
>> +
>> +	return 0;
>> +}
> [ ... ]
>
>> +static __noinline union upair make_upair(__u64 a, __u64 b)
>> +{
>> +	union upair p;
>> +
>> +	p.halves[0] = a + b;
>> +	p.halves[1] = a - b;
>> +	return p;
>> +}
>> +
>> +SEC("tc")
>> +__load_if_JITed()
>> +__success __retval(0)
>> +int aggregate_ret_union_c_test(struct __sk_buff *skb)
>> +{
>> +	__u64 a = skb->len ^ MIX_A;
>> +	__u64 b = skb->len ^ MIX_B;
>> +	union upair p;
>> +
>> +	p = make_upair(a, b);
>> +	if (p.parts.lo != a + b)
>> +		return 1;
>> +	if (p.parts.hi != a - b)
>> +		return 2;
>> +
>> +	return 0;
>> +}
>
> ---
> 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/31740414277