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From: Kui-Feng Lee <kuifeng@meta.com>
To: <bpf@vger.kernel.org>, <ast@kernel.org>, <martin.lau@linux.dev>,
	<song@kernel.org>, <kernel-team@meta.com>, <andrii@kernel.org>,
	<sdf@google.com>
Cc: Kui-Feng Lee <kuifeng@meta.com>
Subject: [PATCH bpf-next v12 7/8] libbpf: Use .struct_ops.link section to indicate a struct_ops with a link.
Date: Wed, 22 Mar 2023 20:24:04 -0700	[thread overview]
Message-ID: <20230323032405.3735486-8-kuifeng@meta.com> (raw)
In-Reply-To: <20230323032405.3735486-1-kuifeng@meta.com>

Flags a struct_ops is to back a bpf_link by putting it to the
".struct_ops.link" section.  Once it is flagged, the created
struct_ops can be used to create a bpf_link or update a bpf_link that
has been backed by another struct_ops.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/libbpf.c | 60 +++++++++++++++++++++++++++++++-----------
 1 file changed, 44 insertions(+), 16 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 2b5ea2500b80..f6a071db5c6e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -468,6 +468,7 @@ struct bpf_struct_ops {
 #define KCONFIG_SEC ".kconfig"
 #define KSYMS_SEC ".ksyms"
 #define STRUCT_OPS_SEC ".struct_ops"
+#define STRUCT_OPS_LINK_SEC ".struct_ops.link"
 
 enum libbpf_map_type {
 	LIBBPF_MAP_UNSPEC,
@@ -597,6 +598,7 @@ struct elf_state {
 	Elf64_Ehdr *ehdr;
 	Elf_Data *symbols;
 	Elf_Data *st_ops_data;
+	Elf_Data *st_ops_link_data;
 	size_t shstrndx; /* section index for section name strings */
 	size_t strtabidx;
 	struct elf_sec_desc *secs;
@@ -606,6 +608,7 @@ struct elf_state {
 	int text_shndx;
 	int symbols_shndx;
 	int st_ops_shndx;
+	int st_ops_link_shndx;
 };
 
 struct usdt_manager;
@@ -1119,7 +1122,8 @@ static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj)
 	return 0;
 }
 
-static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
+static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
+				int shndx, Elf_Data *data, __u32 map_flags)
 {
 	const struct btf_type *type, *datasec;
 	const struct btf_var_secinfo *vsi;
@@ -1130,15 +1134,15 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 	struct bpf_map *map;
 	__u32 i;
 
-	if (obj->efile.st_ops_shndx == -1)
+	if (shndx == -1)
 		return 0;
 
 	btf = obj->btf;
-	datasec_id = btf__find_by_name_kind(btf, STRUCT_OPS_SEC,
+	datasec_id = btf__find_by_name_kind(btf, sec_name,
 					    BTF_KIND_DATASEC);
 	if (datasec_id < 0) {
 		pr_warn("struct_ops init: DATASEC %s not found\n",
-			STRUCT_OPS_SEC);
+			sec_name);
 		return -EINVAL;
 	}
 
@@ -1151,7 +1155,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		type_id = btf__resolve_type(obj->btf, vsi->type);
 		if (type_id < 0) {
 			pr_warn("struct_ops init: Cannot resolve var type_id %u in DATASEC %s\n",
-				vsi->type, STRUCT_OPS_SEC);
+				vsi->type, sec_name);
 			return -EINVAL;
 		}
 
@@ -1170,7 +1174,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		if (IS_ERR(map))
 			return PTR_ERR(map);
 
-		map->sec_idx = obj->efile.st_ops_shndx;
+		map->sec_idx = shndx;
 		map->sec_offset = vsi->offset;
 		map->name = strdup(var_name);
 		if (!map->name)
@@ -1180,6 +1184,7 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		map->def.key_size = sizeof(int);
 		map->def.value_size = type->size;
 		map->def.max_entries = 1;
+		map->def.map_flags = map_flags;
 
 		map->st_ops = calloc(1, sizeof(*map->st_ops));
 		if (!map->st_ops)
@@ -1192,14 +1197,14 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 		if (!st_ops->data || !st_ops->progs || !st_ops->kern_func_off)
 			return -ENOMEM;
 
-		if (vsi->offset + type->size > obj->efile.st_ops_data->d_size) {
+		if (vsi->offset + type->size > data->d_size) {
 			pr_warn("struct_ops init: var %s is beyond the end of DATASEC %s\n",
-				var_name, STRUCT_OPS_SEC);
+				var_name, sec_name);
 			return -EINVAL;
 		}
 
 		memcpy(st_ops->data,
-		       obj->efile.st_ops_data->d_buf + vsi->offset,
+		       data->d_buf + vsi->offset,
 		       type->size);
 		st_ops->tname = tname;
 		st_ops->type = type;
@@ -1212,6 +1217,19 @@ static int bpf_object__init_struct_ops_maps(struct bpf_object *obj)
 	return 0;
 }
 
+static int bpf_object_init_struct_ops(struct bpf_object *obj)
+{
+	int err;
+
+	err = init_struct_ops_maps(obj, STRUCT_OPS_SEC, obj->efile.st_ops_shndx,
+				   obj->efile.st_ops_data, 0);
+	err = err ?: init_struct_ops_maps(obj, STRUCT_OPS_LINK_SEC,
+					  obj->efile.st_ops_link_shndx,
+					  obj->efile.st_ops_link_data,
+					  BPF_F_LINK);
+	return err;
+}
+
 static struct bpf_object *bpf_object__new(const char *path,
 					  const void *obj_buf,
 					  size_t obj_buf_sz,
@@ -1248,6 +1266,7 @@ static struct bpf_object *bpf_object__new(const char *path,
 	obj->efile.obj_buf_sz = obj_buf_sz;
 	obj->efile.btf_maps_shndx = -1;
 	obj->efile.st_ops_shndx = -1;
+	obj->efile.st_ops_link_shndx = -1;
 	obj->kconfig_map_idx = -1;
 
 	obj->kern_version = get_kernel_version();
@@ -1265,6 +1284,7 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
 	obj->efile.elf = NULL;
 	obj->efile.symbols = NULL;
 	obj->efile.st_ops_data = NULL;
+	obj->efile.st_ops_link_data = NULL;
 
 	zfree(&obj->efile.secs);
 	obj->efile.sec_cnt = 0;
@@ -2619,7 +2639,7 @@ static int bpf_object__init_maps(struct bpf_object *obj,
 	err = bpf_object__init_user_btf_maps(obj, strict, pin_root_path);
 	err = err ?: bpf_object__init_global_data_maps(obj);
 	err = err ?: bpf_object__init_kconfig_map(obj);
-	err = err ?: bpf_object__init_struct_ops_maps(obj);
+	err = err ?: bpf_object_init_struct_ops(obj);
 
 	return err;
 }
@@ -2753,12 +2773,13 @@ static bool libbpf_needs_btf(const struct bpf_object *obj)
 {
 	return obj->efile.btf_maps_shndx >= 0 ||
 	       obj->efile.st_ops_shndx >= 0 ||
+	       obj->efile.st_ops_link_shndx >= 0 ||
 	       obj->nr_extern > 0;
 }
 
 static bool kernel_needs_btf(const struct bpf_object *obj)
 {
-	return obj->efile.st_ops_shndx >= 0;
+	return obj->efile.st_ops_shndx >= 0 || obj->efile.st_ops_link_shndx >= 0;
 }
 
 static int bpf_object__init_btf(struct bpf_object *obj,
@@ -3451,6 +3472,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 			} else if (strcmp(name, STRUCT_OPS_SEC) == 0) {
 				obj->efile.st_ops_data = data;
 				obj->efile.st_ops_shndx = idx;
+			} else if (strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {
+				obj->efile.st_ops_link_data = data;
+				obj->efile.st_ops_link_shndx = idx;
 			} else {
 				pr_info("elf: skipping unrecognized data section(%d) %s\n",
 					idx, name);
@@ -3465,6 +3489,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 			/* Only do relo for section with exec instructions */
 			if (!section_have_execinstr(obj, targ_sec_idx) &&
 			    strcmp(name, ".rel" STRUCT_OPS_SEC) &&
+			    strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
 			    strcmp(name, ".rel" MAPS_ELF_SEC)) {
 				pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",
 					idx, name, targ_sec_idx,
@@ -6611,7 +6636,7 @@ static int bpf_object__collect_relos(struct bpf_object *obj)
 			return -LIBBPF_ERRNO__INTERNAL;
 		}
 
-		if (idx == obj->efile.st_ops_shndx)
+		if (idx == obj->efile.st_ops_shndx || idx == obj->efile.st_ops_link_shndx)
 			err = bpf_object__collect_st_ops_relos(obj, shdr, data);
 		else if (idx == obj->efile.btf_maps_shndx)
 			err = bpf_object__collect_map_relos(obj, shdr, data);
@@ -8853,6 +8878,7 @@ const char *libbpf_bpf_prog_type_str(enum bpf_prog_type t)
 }
 
 static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj,
+						     int sec_idx,
 						     size_t offset)
 {
 	struct bpf_map *map;
@@ -8862,7 +8888,8 @@ static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj,
 		map = &obj->maps[i];
 		if (!bpf_map__is_struct_ops(map))
 			continue;
-		if (map->sec_offset <= offset &&
+		if (map->sec_idx == sec_idx &&
+		    map->sec_offset <= offset &&
 		    offset - map->sec_offset < map->def.value_size)
 			return map;
 	}
@@ -8904,7 +8931,7 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
 		}
 
 		name = elf_sym_str(obj, sym->st_name) ?: "<?>";
-		map = find_struct_ops_map_by_offset(obj, rel->r_offset);
+		map = find_struct_ops_map_by_offset(obj, shdr->sh_info, rel->r_offset);
 		if (!map) {
 			pr_warn("struct_ops reloc: cannot find map at rel->r_offset %zu\n",
 				(size_t)rel->r_offset);
@@ -8971,8 +8998,9 @@ static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
 		}
 
 		/* struct_ops BPF prog can be re-used between multiple
-		 * .struct_ops as long as it's the same struct_ops struct
-		 * definition and the same function pointer field
+		 * .struct_ops & .struct_ops.link as long as it's the
+		 * same struct_ops struct definition and the same
+		 * function pointer field
 		 */
 		if (prog->attach_btf_id != st_ops->type_id ||
 		    prog->expected_attach_type != member_idx) {
-- 
2.34.1


  parent reply	other threads:[~2023-03-23  3:27 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-23  3:23 [PATCH bpf-next v12 0/8] Transit between BPF TCP congestion controls Kui-Feng Lee
2023-03-23  3:23 ` [PATCH bpf-next v12 1/8] bpf: Retire the struct_ops map kvalue->refcnt Kui-Feng Lee
2023-03-23  3:23 ` [PATCH bpf-next v12 2/8] net: Update an existing TCP congestion control algorithm Kui-Feng Lee
2023-03-23  3:24 ` [PATCH bpf-next v12 3/8] bpf: Create links for BPF struct_ops maps Kui-Feng Lee
2023-03-23  3:24 ` [PATCH bpf-next v12 4/8] libbpf: Create a bpf_link in bpf_map__attach_struct_ops() Kui-Feng Lee
2023-03-23  3:24 ` [PATCH bpf-next v12 5/8] bpf: Update the struct_ops of a bpf_link Kui-Feng Lee
2023-03-23  3:24 ` [PATCH bpf-next v12 6/8] libbpf: Update a bpf_link with another struct_ops Kui-Feng Lee
2023-03-23  3:24 ` Kui-Feng Lee [this message]
2023-03-23  3:24 ` [PATCH bpf-next v12 8/8] selftests/bpf: Test switching TCP Congestion Control algorithms Kui-Feng Lee
2023-03-23  6:05   ` Martin KaFai Lau
2023-03-23 14:50     ` Kui-Feng Lee
2023-03-23  6:10 ` [PATCH bpf-next v12 0/8] Transit between BPF TCP congestion controls patchwork-bot+netdevbpf

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