Re: [PATCH bpf-next] selftests/bpf: check if distilled base inherits source endianness

[Alan Maguire <alan.maguire@oracle.com>]

On 30/08/2024 18:34, Eduard Zingerman wrote:
> Create a BTF with endianness different from host, make a distilled
> base/split BTF pair from it, dump as raw bytes, import again and
> verify that endianness is preserved.
> 
> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

One small thing below, but

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>

Thanks!

> ---
>  .../selftests/bpf/prog_tests/btf_distill.c    | 73 +++++++++++++++++++
>  1 file changed, 73 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/btf_distill.c b/tools/testing/selftests/bpf/prog_tests/btf_distill.c
> index bfbe795823a2..810b2e434562 100644
> --- a/tools/testing/selftests/bpf/prog_tests/btf_distill.c
> +++ b/tools/testing/selftests/bpf/prog_tests/btf_distill.c
> @@ -535,6 +535,77 @@ static void test_distilled_base_vmlinux(void)
>  	btf__free(vmlinux_btf);
>  }
>  
> +static bool is_host_big_endian(void)
> +{
> +	return htons(0x1234) == 0x1234;
> +}
> +
> +/* Split and new base BTFs should inherit endianness from source BTF. */
> +static void test_distilled_endianness(void)
> +{
> +	struct btf *base = NULL, *split = NULL, *new_base = NULL, *new_split = NULL;
> +	struct btf *new_base1 = NULL, *new_split1 = NULL;
> +	enum btf_endianness inverse_endianness;
> +	const void *raw_data;
> +	__u32 size;
> +
> +	printf("is_host_big_endian? %d\n", is_host_big_endian());
> +	inverse_endianness = is_host_big_endian() ? BTF_LITTLE_ENDIAN : BTF_BIG_ENDIAN;
> +	base = btf__new_empty();


nit: I think you could avoid the need for is_host_big_endian() by doing
this:

inverse_endianness = btf__endianness(base) == BTF_LITTLE_ENDIAN ?
		     BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN;


> +	btf__set_endianness(base, inverse_endianness);
> +	if (!ASSERT_OK_PTR(base, "empty_main_btf"))
> +		return;
> +	btf__add_int(base, "int", 4, BTF_INT_SIGNED);   /* [1] int */
> +	VALIDATE_RAW_BTF(
> +		base,
> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED");
> +	split = btf__new_empty_split(base);
> +	if (!ASSERT_OK_PTR(split, "empty_split_btf"))
> +		goto cleanup;
> +	btf__add_ptr(split, 1);
> +	VALIDATE_RAW_BTF(
> +		split,
> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
> +		"[2] PTR '(anon)' type_id=1");
> +	if (!ASSERT_EQ(0, btf__distill_base(split, &new_base, &new_split),
> +		       "distilled_base") ||
> +	    !ASSERT_OK_PTR(new_base, "distilled_base") ||
> +	    !ASSERT_OK_PTR(new_split, "distilled_split") ||
> +	    !ASSERT_EQ(2, btf__type_cnt(new_base), "distilled_base_type_cnt"))
> +		goto cleanup;
> +	VALIDATE_RAW_BTF(
> +		new_split,
> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
> +		"[2] PTR '(anon)' type_id=1");
> +
> +	raw_data = btf__raw_data(new_base, &size);
> +	if (!ASSERT_OK_PTR(raw_data, "btf__raw_data #1"))
> +		goto cleanup;
> +	new_base1 = btf__new(raw_data, size);
> +	if (!ASSERT_OK_PTR(new_base1, "new_base1 = btf__new()"))
> +		goto cleanup;
> +	raw_data = btf__raw_data(new_split, &size);
> +	if (!ASSERT_OK_PTR(raw_data, "btf__raw_data #2"))
> +		goto cleanup;
> +	new_split1 = btf__new_split(raw_data, size, new_base1);
> +	if (!ASSERT_OK_PTR(new_split1, "new_split1 = btf__new()"))
> +		goto cleanup;
> +
> +	ASSERT_EQ(btf__endianness(new_base1), inverse_endianness, "new_base1 endianness");
> +	ASSERT_EQ(btf__endianness(new_split1), inverse_endianness, "new_split1 endianness");
> +	VALIDATE_RAW_BTF(
> +		new_split1,
> +		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
> +		"[2] PTR '(anon)' type_id=1");
> +cleanup:
> +	btf__free(new_split1);
> +	btf__free(new_base1);
> +	btf__free(new_split);
> +	btf__free(new_base);
> +	btf__free(split);
> +	btf__free(base);
> +}
> +
>  void test_btf_distill(void)
>  {
>  	if (test__start_subtest("distilled_base"))
> @@ -549,4 +620,6 @@ void test_btf_distill(void)
>  		test_distilled_base_multi_err2();
>  	if (test__start_subtest("distilled_base_vmlinux"))
>  		test_distilled_base_vmlinux();
> +	if (test__start_subtest("distilled_endianness"))
> +		test_distilled_endianness();
>  }