Re: [PATCH bpf-next 09/12] selftests/bpf: Add C tests for 16-byte returns in R0:R2

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2026-07-08 at 13:10 -0700, Yonghong Song wrote:
> Add selftests that exercise a 16-byte return value passed in the R0:R2
> register pair, expressed in C so they rely on the compiler lowering the
> register-pair return. Tests include an __int128 return (from a subprogram
> and a kfunc), a 16-byte struct return (from static and global subprograms
> and a kfunc) and a 16-byte union return.
> 
> The R0:R2 return convention is only emitted by LLVM 23 and newer, so the
> programs are gated on __clang_major__ >= 23; with an older compiler they
> return a sentinel and the "int128_c", "struct_c", "global_struct_c",
> "kfunc_struct_c" and "union_c" subtests are skipped.
> 
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---

[...]

> +static void run_prog(struct bpf_program *prog, bool may_skip)
> +{
> +	char buf[64] = {};
> +	LIBBPF_OPTS(bpf_test_run_opts, topts,
> +		.data_in = buf,
> +		.data_size_in = sizeof(buf),
> +		.repeat = 1,
> +	);
> +	int err;
> +
> +	err = bpf_prog_test_run_opts(bpf_program__fd(prog), &topts);
> +	if (!ASSERT_OK(err, "test_run"))
> +		return;
> +
> +	if (may_skip && (int)topts.retval == -1) {
> +		test__skip();
> +		return;
> +	}
> +
> +	ASSERT_EQ(topts.retval, 0, "aggregate_ret_result");
> +}
> +
> +void test_aggregate_ret(void)
> +{

The test_aggregate_ret()/run_prog() duplicate functionality provided
by the __retval tag from test_loader.c. To achieve the same skipping
mechanics I suggest to:
- extend test_loader.c / bpf_misc.h with a new tag: __skip("reason")
- use this tag as:

  #ifdef __clang_major__ >= 23

  SEC("tc")
  int aggregate_ret_test(struct __sk_buff *skb) { ... }

  #else

  SEC("tc") __skip("... need clang23 ...")
  int aggregate_ret_test(struct __sk_buff *skb) { ... }

  #endif

[...]

> diff --git a/tools/testing/selftests/bpf/progs/aggregate_ret_int128_c.c ...
> diff --git a/tools/testing/selftests/bpf/progs/aggregate_ret_struct_c.c ...
> diff --git a/tools/testing/selftests/bpf/progs/aggregate_ret_union_c.c ...

Nit: all three files can be merged into one.

[...]