Commit 342bf525 authored by Donglin Peng's avatar Donglin Peng Committed by Andrii Nakryiko
Browse files

btf: Verify BTF sorting 



This patch checks whether the BTF is sorted by name in ascending order.
If sorted, binary search will be used when looking up types.

Specifically, vmlinux and kernel module BTFs are always sorted during
the build phase with anonymous types placed before named types, so we
only need to identify the starting ID of named types.

Signed-off-by: default avatarDonglin Peng <pengdonglin@xiaomi.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260109130003.3313716-8-dolinux.peng@gmail.com
parent 8c3070e1

kernel/bpf/btf.c

+43 −0
Original line number Diff line number Diff line
@@ -550,6 +550,47 @@ u32 btf_nr_types(const struct btf *btf) 
	return total;

}



/*

 * Note that vmlinux and kernel module BTFs are always sorted

 * during the building phase.

 */

static void btf_check_sorted(struct btf *btf)

{

	u32 i, n, named_start_id = 0;



	n = btf_nr_types(btf);

	if (btf_is_vmlinux(btf)) {

		for (i = btf_start_id(btf); i < n; i++) {

			const struct btf_type *t = btf_type_by_id(btf, i);

			const char *n = btf_name_by_offset(btf, t->name_off);



			if (n[0] != '\0') {

				btf->named_start_id = i;

				return;

			}

		}

		return;

	}



	for (i = btf_start_id(btf) + 1; i < n; i++) {

		const struct btf_type *ta = btf_type_by_id(btf, i - 1);

		const struct btf_type *tb = btf_type_by_id(btf, i);

		const char *na = btf_name_by_offset(btf, ta->name_off);

		const char *nb = btf_name_by_offset(btf, tb->name_off);



		if (strcmp(na, nb) > 0)

			return;



		if (named_start_id == 0 && na[0] != '\0')

			named_start_id = i - 1;

		if (named_start_id == 0 && nb[0] != '\0')

			named_start_id = i;

	}



	if (named_start_id)

		btf->named_start_id = named_start_id;

}



/*

 * btf_named_start_id - Get the named starting ID for the BTF

 * @btf: Pointer to the target BTF object
@@ -6301,6 +6342,7 @@ static struct btf *btf_parse_base(struct btf_verifier_env *env, const char *name 
	if (err)

		goto errout;



	btf_check_sorted(btf);

	refcount_set(&btf->refcnt, 1);



	return btf;
@@ -6435,6 +6477,7 @@ static struct btf *btf_parse_module(const char *module_name, const void *data, 
	}



	btf_verifier_env_free(env);

	btf_check_sorted(btf);

	refcount_set(&btf->refcnt, 1);

	return btf;