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From: "Mauricio Vásquez" <mauricio@kinvolk.io>
To: netdev@vger.kernel.org, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Quentin Monnet <quentin@isovalent.com>,
	Rafael David Tinoco <rafaeldtinoco@gmail.com>,
	Lorenzo Fontana <lorenzo.fontana@elastic.co>,
	Leonardo Di Donato <leonardo.didonato@elastic.co>
Subject: [PATCH bpf-next v7 5/7] bpftool: Implement btfgen_get_btf()
Date: Tue, 15 Feb 2022 17:58:54 -0500	[thread overview]
Message-ID: <20220215225856.671072-6-mauricio@kinvolk.io> (raw)
In-Reply-To: <20220215225856.671072-1-mauricio@kinvolk.io>

The last part of the BTFGen algorithm is to create a new BTF object with
all the types that were recorded in the previous steps.

This function performs two different steps:
1. Add the types to the new BTF object by using btf__add_type(). Some
special logic around struct and unions is implemented to only add the
members that are really used in the field-based relocations. The type
ID on the new and old BTF objects is stored on a map.
2. Fix all the type IDs on the new BTF object by using the IDs saved in
the previous step.

Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
---
 tools/bpf/bpftool/gen.c | 100 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 99 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 806001020841..25a336846d9f 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -1505,10 +1505,108 @@ static int btfgen_record_obj(struct btfgen_info *info, const char *obj_path)
 	return err;
 }
 
+static int btfgen_remap_id(__u32 *type_id, void *ctx)
+{
+	unsigned int *ids = ctx;
+
+	*type_id = ids[*type_id];
+
+	return 0;
+}
+
 /* Generate BTF from relocation information previously recorded */
 static struct btf *btfgen_get_btf(struct btfgen_info *info)
 {
-	return ERR_PTR(-EOPNOTSUPP);
+	struct btf *btf_new = NULL;
+	unsigned int *ids = NULL;
+	unsigned int i, n = btf__type_cnt(info->marked_btf);
+	int err = 0;
+
+	btf_new = btf__new_empty();
+	if (!btf_new) {
+		err = -errno;
+		goto err_out;
+	}
+
+	ids = calloc(n, sizeof(*ids));
+	if (!ids) {
+		err = -errno;
+		goto err_out;
+	}
+
+	/* first pass: add all marked types to btf_new and add their new ids to the ids map */
+	for (i = 1; i < n; i++) {
+		const struct btf_type *cloned_type, *type;
+		const char *name;
+		int new_id;
+
+		cloned_type = btf__type_by_id(info->marked_btf, i);
+
+		if (cloned_type->name_off != MARKED)
+			continue;
+
+		type = btf__type_by_id(info->src_btf, i);
+
+		/* add members for struct and union */
+		if (btf_is_composite(type)) {
+			struct btf_member *cloned_m, *m;
+			unsigned short vlen;
+			int idx_src;
+
+			name = btf__str_by_offset(info->src_btf, type->name_off);
+
+			if (btf_is_struct(type))
+				err = btf__add_struct(btf_new, name, type->size);
+			else
+				err = btf__add_union(btf_new, name, type->size);
+
+			if (err < 0)
+				goto err_out;
+			new_id = err;
+
+			cloned_m = btf_members(cloned_type);
+			m = btf_members(type);
+			vlen = btf_vlen(cloned_type);
+			for (idx_src = 0; idx_src < vlen; idx_src++, cloned_m++, m++) {
+				/* add only members that are marked as used */
+				if (cloned_m->name_off != MARKED)
+					continue;
+
+				name = btf__str_by_offset(info->src_btf, m->name_off);
+				err = btf__add_field(btf_new, name, m->type,
+						     BTF_MEMBER_BIT_OFFSET(m->offset),
+						     BTF_MEMBER_BITFIELD_SIZE(m->offset));
+				if (err < 0)
+					goto err_out;
+			}
+		} else {
+			err = btf__add_type(btf_new, info->src_btf, type);
+			if (err < 0)
+				goto err_out;
+			new_id = err;
+		}
+
+		/* add ID mapping */
+		ids[i] = new_id;
+	}
+
+	/* second pass: fix up type ids */
+	for (i = 1; i < btf__type_cnt(btf_new); i++) {
+		struct btf_type *btf_type = (struct btf_type *) btf__type_by_id(btf_new, i);
+
+		err = btf_type_visit_type_ids(btf_type, btfgen_remap_id, ids);
+		if (err)
+			goto err_out;
+	}
+
+	free(ids);
+	return btf_new;
+
+err_out:
+	btf__free(btf_new);
+	free(ids);
+	errno = -err;
+	return NULL;
 }
 
 /* Create minimized BTF file for a set of BPF objects.
-- 
2.25.1


  parent reply	other threads:[~2022-02-15 22:59 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-15 22:58 [PATCH bpf-next v7 0/7] libbpf: Implement BTFGen Mauricio Vásquez
2022-02-15 22:58 ` [PATCH bpf-next v7 1/7] libbpf: split bpf_core_apply_relo() Mauricio Vásquez
2022-02-16  1:52   ` Alexei Starovoitov
2022-02-15 22:58 ` [PATCH bpf-next v7 2/7] libbpf: Expose bpf_core_{add,free}_cands() to bpftool Mauricio Vásquez
2022-02-15 22:58 ` [PATCH bpf-next v7 3/7] bpftool: Add gen min_core_btf command Mauricio Vásquez
2022-02-15 22:58 ` [PATCH bpf-next v7 4/7] bpftool: Implement "gen min_core_btf" logic Mauricio Vásquez
2022-02-18 16:20   ` Quentin Monnet
2022-02-18 19:43     ` Mauricio Vásquez Bernal
2022-02-18 19:48       ` Andrii Nakryiko
2022-02-18 19:52         ` Quentin Monnet
2022-02-15 22:58 ` Mauricio Vásquez [this message]
2022-02-16 18:20   ` [PATCH bpf-next v7 5/7] bpftool: Implement btfgen_get_btf() Andrii Nakryiko
2022-02-15 22:58 ` [PATCH bpf-next v7 6/7] bpftool: gen min_core_btf explanation and examples Mauricio Vásquez
2022-02-16 18:20   ` Andrii Nakryiko
2022-02-15 22:58 ` [PATCH bpf-next v7 7/7] selftests/bpf: Test "bpftool gen min_core_btf" Mauricio Vásquez
2022-02-16 18:20   ` Andrii Nakryiko
2022-02-16 18:20 ` [PATCH bpf-next v7 0/7] libbpf: Implement BTFGen Andrii Nakryiko
2022-02-17 22:07   ` Mauricio Vásquez Bernal
2022-02-17 22:12     ` Andrii Nakryiko
2022-02-16 18:30 ` patchwork-bot+netdevbpf

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