Commit 0849e102 authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

Merge branch 'support-flex-arrays' 



Andrii Nakryiko says:

====================
Add support for flexible array accesses in a relocatable manner in BPF CO-RE.
It's a typical pattern in C, and kernel in particular, to provide
a fixed-length struct with zero-sized or dimensionless array at the end. In
such cases variable-sized array contents follows immediately after the end of
a struct. This patch set adds support for such access pattern by allowing
accesses to such arrays.

Patch #1 adds libbpf support. Patch #2 adds few test cases for validation.
====================

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parents 01c6f7aa 5f2eecef

tools/lib/bpf/libbpf.c

+29 −5
Original line number Diff line number Diff line
@@ -3108,6 +3108,21 @@ static bool str_is_empty(const char *s) 
	return !s || !s[0];

}



static bool is_flex_arr(const struct btf *btf,

			const struct bpf_core_accessor *acc,

			const struct btf_array *arr)

{

	const struct btf_type *t;



	/* not a flexible array, if not inside a struct or has non-zero size */

	if (!acc->name || arr->nelems > 0)

		return false;



	/* has to be the last member of enclosing struct */

	t = btf__type_by_id(btf, acc->type_id);

	return acc->idx == btf_vlen(t) - 1;

}



/*

 * Turn bpf_field_reloc into a low- and high-level spec representation,

 * validating correctness along the way, as well as calculating resulting
@@ -3145,6 +3160,7 @@ static int bpf_core_spec_parse(const struct btf *btf, 
			       struct bpf_core_spec *spec)

{

	int access_idx, parsed_len, i;

	struct bpf_core_accessor *acc;

	const struct btf_type *t;

	const char *name;

	__u32 id;
@@ -3192,6 +3208,7 @@ static int bpf_core_spec_parse(const struct btf *btf, 
			return -EINVAL;



		access_idx = spec->raw_spec[i];

		acc = &spec->spec[spec->len];



		if (btf_is_composite(t)) {

			const struct btf_member *m;
@@ -3209,18 +3226,23 @@ static int bpf_core_spec_parse(const struct btf *btf, 
				if (str_is_empty(name))

					return -EINVAL;



				spec->spec[spec->len].type_id = id;

				spec->spec[spec->len].idx = access_idx;

				spec->spec[spec->len].name = name;

				acc->type_id = id;

				acc->idx = access_idx;

				acc->name = name;

				spec->len++;

			}



			id = m->type;

		} else if (btf_is_array(t)) {

			const struct btf_array *a = btf_array(t);

			bool flex;



			t = skip_mods_and_typedefs(btf, a->type, &id);

			if (!t || access_idx >= a->nelems)

			if (!t)

				return -EINVAL;



			flex = is_flex_arr(btf, acc - 1, a);

			if (!flex && access_idx >= a->nelems)

				return -EINVAL;



			spec->spec[spec->len].type_id = id;
@@ -3525,12 +3547,14 @@ static int bpf_core_spec_match(struct bpf_core_spec *local_spec, 
			 */

			if (i > 0) {

				const struct btf_array *a;

				bool flex;



				if (!btf_is_array(targ_type))

					return 0;



				a = btf_array(targ_type);

				if (local_acc->idx >= a->nelems)

				flex = is_flex_arr(targ_btf, targ_acc - 1, a);

				if (!flex && local_acc->idx >= a->nelems)

					return 0;

				if (!skip_mods_and_typedefs(targ_btf, a->type,

							    &targ_id))

tools/testing/selftests/bpf/prog_tests/core_reloc.c

+4 −0
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ 
		.b123 = 2,						\

		.c1c  = 3,						\

		.d00d = 4,						\

		.f10c = 0,						\

	},								\

	.output_len = sizeof(struct core_reloc_arrays_output)		\

}
@@ -308,12 +309,15 @@ static struct core_reloc_test_case test_cases[] = { 
	ARRAYS_CASE(arrays),

	ARRAYS_CASE(arrays___diff_arr_dim),

	ARRAYS_CASE(arrays___diff_arr_val_sz),

	ARRAYS_CASE(arrays___equiv_zero_sz_arr),

	ARRAYS_CASE(arrays___fixed_arr),



	ARRAYS_ERR_CASE(arrays___err_too_small),

	ARRAYS_ERR_CASE(arrays___err_too_shallow),

	ARRAYS_ERR_CASE(arrays___err_non_array),

	ARRAYS_ERR_CASE(arrays___err_wrong_val_type1),

	ARRAYS_ERR_CASE(arrays___err_wrong_val_type2),

	ARRAYS_ERR_CASE(arrays___err_bad_zero_sz_arr),



	/* enum/ptr/int handling scenarios */

	PRIMITIVES_CASE(primitives),

tools/testing/selftests/bpf/progs/btf__core_reloc_arrays___equiv_zero_sz_arr.c

0 → 100644
+3 −0
Original line number Diff line number Diff line 
#include "core_reloc_types.h"



void f(struct core_reloc_arrays___equiv_zero_sz_arr x) {}

tools/testing/selftests/bpf/progs/btf__core_reloc_arrays___err_bad_zero_sz_arr.c

0 → 100644
+3 −0
Original line number Diff line number Diff line 
#include "core_reloc_types.h"



void f(struct core_reloc_arrays___err_bad_zero_sz_arr x) {}

tools/testing/selftests/bpf/progs/btf__core_reloc_arrays___fixed_arr.c

0 → 100644
+3 −0
Original line number Diff line number Diff line 
#include "core_reloc_types.h"



void f(struct core_reloc_arrays___fixed_arr x) {}

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