Re: [PATCH bpf-next v1 4/4] selftests/bpf: Check that sorting preserves types in bpftool dump

[Eduard Zingerman <eddyz87@gmail.com>]

On Wed, 2026-08-19 at 17:06 -0700, Ihor Solodrai wrote:

...

> @@ -87,6 +90,36 @@ static struct btf *mk_btf(void)
>  	if (!ASSERT_OK(err, "holey_tail"))
>  		goto err_out;
>  
> +	for (i = 0; i < 3; i++) {

Testing this locally, a single enum suffices to showcase the bug,
why the complication?

> +		char name[16];
> +
> +		snprintf(name, sizeof(name), "E%d", i);
> +
> +		id = btf__add_enum(btf, NULL, 4);
> +		if (!ASSERT_GT(id, 0, "anon_enum"))
> +			goto err_out;
> +
> +		err = btf__add_enum_value(btf, name, i + 1);
> +		if (!ASSERT_OK(err, "enum_val"))
> +			goto err_out;
> +	}
> +
> +	id = btf__add_struct(btf, "s", 4);
> +	if (!ASSERT_GT(id, 0, "struct_s"))
> +		goto err_out;
> +
> +	err = btf__add_field(btf, "f", 1, 0, 0);
> +	if (!ASSERT_OK(err, "s_field"))
> +		goto err_out;
> +
> +	id = btf__add_union(btf, "u", 4);
> +	if (!ASSERT_GT(id, 0, "union_u"))
> +		goto err_out;
> +
> +	err = btf__add_field(btf, "f", 1, 0, 0);
> +	if (!ASSERT_OK(err, "u_field"))
> +		goto err_out;
> +
>  	btf__set_pointer_size(btf, 4);
>  
>  	return btf;
> @@ -95,6 +128,42 @@ static struct btf *mk_btf(void)

...

> +static void test_sort_preserves_types(const char *path)
> +{
> +	char *sorted = NULL, *unsorted = NULL;
> +	int n_sorted, n_unsorted;
> +
> +	sorted = dump_c(path, true);
> +	unsorted = dump_c(path, false);
> +	if (!sorted || !unsorted)
> +		goto out;
> +
> +	/*
> +	 * Count definitions by the closing brace in their first column. Counting
> +	 * "struct"/"union"/"enum" openers instead would also count forward
> +	 * declarations, and which types need one depends on emission order.
> +	 */
> +	n_unsorted = count_substr(unsorted, "\n}");
> +	n_sorted = count_substr(sorted, "\n}");

This does not include e.g. typedef. I'd just match for presence of enum.
Or better yet, compare full expected output with actual one and tailor
several BTF definitions, each for a specific sub-test.

> +	ASSERT_GT(n_unsorted, 0, "types_emitted");
> +	ASSERT_EQ(n_sorted, n_unsorted, "same_type_count");
> +
> +out:
> +	free(sorted);
> +	free(unsorted);
> +}
> +
>  /*
>   * Check only what the selftests build cannot:
>   *   - bpf_helpers.h defines __ksym and __weak as well, and no program uses

...