[RFC PATCH bpf-next 0/5] Integrate kernel module BTF support

[RFC PATCH bpf-next 0/5] Integrate kernel module BTF support

[Andrii Nakryiko]

This patch set adds BTF generation for kernel modules using a compact split BTF
approach. Respective patches have all the details.

New Kconfig CONFIG_DEBUG_INTO_BTF_MODULES is added, which is defaulted to y,
but is conditional on pahole v1.19 version, which is going to have a support
for --btf_base flag, providing ability to generate deduplicated split BTF.

This patch set implements in-kernel support for split BTF loading and
validation. It also extends GET_OBJ_INFO API for BTFs to return BTF's module
name and a flag whether BTF itself is in-kernel or user-provided. vmlinux BTF
is also exposed to user-space through the same BTF object iteration APIs.

Follow up patch set will utilize the fact that vmlinux and module BTFs now
have ID associated with them to provide ability to attach BPF fentry/fexit/etc
programs to functions defined in kernel modules.

bpftool is also extended to show module/vmlinux BTF's name.

This patch set is posted as an RFC because it depends on two not yet landed
set of patches:
  - libbpf split BTF support ([0]);
  - pahole's support for split BTF generation and deduplication ([1]).

  [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=377859&state=*
  [1] https://lore.kernel.org/dwarves/20201105043936.2555804-1-andrii@kernel.org/T/#u

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>

Andrii Nakryiko (5):
  bpf: add in-kernel split BTF support
  bpf: assign ID to vmlinux BTF and return extra info for BTF in
    GET_OBJ_INFO
  kbuild: Add CONFIG_DEBUG_INFO_BTF_MODULES option or module BTFs
  bpf: load and verify kernel module BTFs
  tools/bpftool: add support for in-kernel and named BTF in `btf show`

 include/linux/bpf.h            |   2 +
 include/linux/module.h         |   4 +
 include/uapi/linux/bpf.h       |   3 +
 kernel/bpf/btf.c               | 411 ++++++++++++++++++++++++++++-----
 kernel/bpf/sysfs_btf.c         |   2 +-
 kernel/module.c                |  32 +++
 lib/Kconfig.debug              |  10 +
 scripts/Makefile.modfinal      |  20 +-
 tools/bpf/bpftool/btf.c        |  30 ++-
 tools/include/uapi/linux/bpf.h |   3 +
 10 files changed, 460 insertions(+), 57 deletions(-)

-- 
2.24.1

[RFC PATCH bpf-next 1/5] bpf: add in-kernel split BTF support

[Andrii Nakryiko]

Adjust in-kernel BTF implementation to support a split BTF mode of operation.
Changes are mostly mirroring libbpf split BTF changes, with the exception of
start_id being 0 for in-kernel implementation due to simpler read-only mode.

Otherwise, for split BTF logic, most of the logic of jumping to base BTF,
where necessary, is encapsulated in few helper functions. Type numbering and
string offset in a split BTF are logically continuing where base BTF ends, so
most of the high-level logic is kept without changes.

Type verification and size resolution is only doing an added resolution of new
split BTF types and relies on already cached size and type resolution results
in the base BTF.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/bpf/btf.c | 182 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 130 insertions(+), 52 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index ed7d02e8bc93..f61944a3873b 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -204,12 +204,17 @@ struct btf {
 	const char *strings;
 	void *nohdr_data;
 	struct btf_header hdr;
-	u32 nr_types;
+	u32 nr_types; /* includes VOID for base BTF */
 	u32 types_size;
 	u32 data_size;
 	refcount_t refcnt;
 	u32 id;
 	struct rcu_head rcu;
+
+	/* split BTF support */
+	struct btf *base_btf;
+	u32 start_id; /* first type ID in this BTF (0 for base BTF) */
+	u32 start_str_off; /* first string offset (0 for base BTF) */
 };
 
 enum verifier_phase {
@@ -450,14 +455,27 @@ static bool btf_type_is_datasec(const struct btf_type *t)
 	return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC;
 }
 
+static u32 btf_nr_types_total(const struct btf *btf)
+{
+	u32 total = 0;
+
+	while (btf) {
+		total += btf->nr_types;
+		btf = btf->base_btf;
+	}
+
+	return total;
+}
+
 s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind)
 {
 	const struct btf_type *t;
 	const char *tname;
-	u32 i;
+	u32 i, total;
 
-	for (i = 1; i <= btf->nr_types; i++) {
-		t = btf->types[i];
+	total = btf_nr_types_total(btf);
+	for (i = 1; i < total; i++) {
+		t = btf_type_by_id(btf, i);
 		if (BTF_INFO_KIND(t->info) != kind)
 			continue;
 
@@ -600,8 +618,15 @@ static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
 
 static bool btf_name_offset_valid(const struct btf *btf, u32 offset)
 {
-	return BTF_STR_OFFSET_VALID(offset) &&
-		offset < btf->hdr.str_len;
+	if (!BTF_STR_OFFSET_VALID(offset))
+		return false;
+again:
+	if (offset < btf->start_str_off) {
+		btf = btf->base_btf;
+		goto again;
+	}
+	offset -= btf->start_str_off;
+	return offset < btf->hdr.str_len;
 }
 
 static bool __btf_name_char_ok(char c, bool first, bool dot_ok)
@@ -615,10 +640,25 @@ static bool __btf_name_char_ok(char c, bool first, bool dot_ok)
 	return true;
 }
 
+static const char *btf_str_by_offset(const struct btf *btf, u32 offset)
+{
+again:
+	if (offset < btf->start_str_off) {
+		btf = btf->base_btf;
+		goto again;
+	}
+
+	offset -= btf->start_str_off;
+	if (offset < btf->hdr.str_len)
+		return &btf->strings[offset];
+
+	return NULL;
+}
+
 static bool __btf_name_valid(const struct btf *btf, u32 offset, bool dot_ok)
 {
 	/* offset must be valid */
-	const char *src = &btf->strings[offset];
+	const char *src = btf_str_by_offset(btf, offset);
 	const char *src_limit;
 
 	if (!__btf_name_char_ok(*src, true, dot_ok))
@@ -651,27 +691,31 @@ static bool btf_name_valid_section(const struct btf *btf, u32 offset)
 
 static const char *__btf_name_by_offset(const struct btf *btf, u32 offset)
 {
+	const char *name;
+
 	if (!offset)
 		return "(anon)";
-	else if (offset < btf->hdr.str_len)
-		return &btf->strings[offset];
-	else
-		return "(invalid-name-offset)";
+
+	name = btf_str_by_offset(btf, offset);
+	return name ?: "(invalid-name-offset)";
 }
 
 const char *btf_name_by_offset(const struct btf *btf, u32 offset)
 {
-	if (offset < btf->hdr.str_len)
-		return &btf->strings[offset];
-
-	return NULL;
+	return btf_str_by_offset(btf, offset);
 }
 
 const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id)
 {
-	if (type_id > btf->nr_types)
-		return NULL;
+again:
+	if (type_id < btf->start_id) {
+		btf = btf->base_btf;
+		goto again;
+	}
 
+	type_id -= btf->start_id;
+	if (type_id >= btf->nr_types)
+		return NULL;
 	return btf->types[type_id];
 }
 
@@ -1391,17 +1435,13 @@ static int btf_add_type(struct btf_verifier_env *env, struct btf_type *t)
 {
 	struct btf *btf = env->btf;
 
-	/* < 2 because +1 for btf_void which is always in btf->types[0].
-	 * btf_void is not accounted in btf->nr_types because btf_void
-	 * does not come from the BTF file.
-	 */
-	if (btf->types_size - btf->nr_types < 2) {
+	if (btf->types_size == btf->nr_types) {
 		/* Expand 'types' array */
 
 		struct btf_type **new_types;
 		u32 expand_by, new_size;
 
-		if (btf->types_size == BTF_MAX_TYPE) {
+		if (btf->start_id + btf->types_size == BTF_MAX_TYPE) {
 			btf_verifier_log(env, "Exceeded max num of types");
 			return -E2BIG;
 		}
@@ -1415,18 +1455,23 @@ static int btf_add_type(struct btf_verifier_env *env, struct btf_type *t)
 		if (!new_types)
 			return -ENOMEM;
 
-		if (btf->nr_types == 0)
-			new_types[0] = &btf_void;
-		else
+		if (btf->nr_types == 0) {
+			if (!btf->base_btf) {
+				/* lazily init VOID type */
+				new_types[0] = &btf_void;
+				btf->nr_types++;
+			}
+		} else {
 			memcpy(new_types, btf->types,
-			       sizeof(*btf->types) * (btf->nr_types + 1));
+			       sizeof(*btf->types) * btf->nr_types);
+		}
 
 		kvfree(btf->types);
 		btf->types = new_types;
 		btf->types_size = new_size;
 	}
 
-	btf->types[++(btf->nr_types)] = t;
+	btf->types[btf->nr_types++] = t;
 
 	return 0;
 }
@@ -1499,18 +1544,17 @@ static int env_resolve_init(struct btf_verifier_env *env)
 	u32 *resolved_ids = NULL;
 	u8 *visit_states = NULL;
 
-	/* +1 for btf_void */
-	resolved_sizes = kvcalloc(nr_types + 1, sizeof(*resolved_sizes),
+	resolved_sizes = kvcalloc(nr_types, sizeof(*resolved_sizes),
 				  GFP_KERNEL | __GFP_NOWARN);
 	if (!resolved_sizes)
 		goto nomem;
 
-	resolved_ids = kvcalloc(nr_types + 1, sizeof(*resolved_ids),
+	resolved_ids = kvcalloc(nr_types, sizeof(*resolved_ids),
 				GFP_KERNEL | __GFP_NOWARN);
 	if (!resolved_ids)
 		goto nomem;
 
-	visit_states = kvcalloc(nr_types + 1, sizeof(*visit_states),
+	visit_states = kvcalloc(nr_types, sizeof(*visit_states),
 				GFP_KERNEL | __GFP_NOWARN);
 	if (!visit_states)
 		goto nomem;
@@ -1562,21 +1606,27 @@ static bool env_type_is_resolve_sink(const struct btf_verifier_env *env,
 static bool env_type_is_resolved(const struct btf_verifier_env *env,
 				 u32 type_id)
 {
-	return env->visit_states[type_id] == RESOLVED;
+	/* base BTF types should be resolved by now */
+	if (type_id < env->btf->start_id)
+		return true;
+
+	return env->visit_states[type_id - env->btf->start_id] == RESOLVED;
 }
 
 static int env_stack_push(struct btf_verifier_env *env,
 			  const struct btf_type *t, u32 type_id)
 {
+	const struct btf *btf = env->btf;
 	struct resolve_vertex *v;
 
 	if (env->top_stack == MAX_RESOLVE_DEPTH)
 		return -E2BIG;
 
-	if (env->visit_states[type_id] != NOT_VISITED)
+	if (type_id < btf->start_id
+	    || env->visit_states[type_id - btf->start_id] != NOT_VISITED)
 		return -EEXIST;
 
-	env->visit_states[type_id] = VISITED;
+	env->visit_states[type_id - btf->start_id] = VISITED;
 
 	v = &env->stack[env->top_stack++];
 	v->t = t;
@@ -1606,6 +1656,7 @@ static void env_stack_pop_resolved(struct btf_verifier_env *env,
 	u32 type_id = env->stack[--(env->top_stack)].type_id;
 	struct btf *btf = env->btf;
 
+	type_id -= btf->start_id; /* adjust to local type id */
 	btf->resolved_sizes[type_id] = resolved_size;
 	btf->resolved_ids[type_id] = resolved_type_id;
 	env->visit_states[type_id] = RESOLVED;
@@ -1710,14 +1761,34 @@ btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 	return __btf_resolve_size(btf, type, type_size, NULL, NULL, NULL, NULL);
 }
 
+static u32 btf_resolved_type_id(const struct btf *btf, u32 type_id)
+{
+again:
+	if (type_id < btf->start_id) {
+		btf = btf->base_btf;
+		goto again;
+	}
+	return btf->resolved_ids[type_id - btf->start_id];
+}
+
 /* The input param "type_id" must point to a needs_resolve type */
 static const struct btf_type *btf_type_id_resolve(const struct btf *btf,
 						  u32 *type_id)
 {
-	*type_id = btf->resolved_ids[*type_id];
+	*type_id = btf_resolved_type_id(btf, *type_id);
 	return btf_type_by_id(btf, *type_id);
 }
 
+static u32 btf_resolved_type_size(const struct btf *btf, u32 type_id)
+{
+again:
+	if (type_id < btf->start_id) {
+		btf = btf->base_btf;
+		goto again;
+	}
+	return btf->resolved_sizes[type_id - btf->start_id];
+}
+
 const struct btf_type *btf_type_id_size(const struct btf *btf,
 					u32 *type_id, u32 *ret_size)
 {
@@ -1732,7 +1803,7 @@ const struct btf_type *btf_type_id_size(const struct btf *btf,
 	if (btf_type_has_size(size_type)) {
 		size = size_type->size;
 	} else if (btf_type_is_array(size_type)) {
-		size = btf->resolved_sizes[size_type_id];
+		size = btf_resolved_type_size(btf, size_type_id);
 	} else if (btf_type_is_ptr(size_type)) {
 		size = sizeof(void *);
 	} else {
@@ -1740,14 +1811,14 @@ const struct btf_type *btf_type_id_size(const struct btf *btf,
 				 !btf_type_is_var(size_type)))
 			return NULL;
 
-		size_type_id = btf->resolved_ids[size_type_id];
+		size_type_id = btf_resolved_type_id(btf, size_type_id);
 		size_type = btf_type_by_id(btf, size_type_id);
 		if (btf_type_nosize_or_null(size_type))
 			return NULL;
 		else if (btf_type_has_size(size_type))
 			size = size_type->size;
 		else if (btf_type_is_array(size_type))
-			size = btf->resolved_sizes[size_type_id];
+			size = btf_resolved_type_size(btf, size_type_id);
 		else if (btf_type_is_ptr(size_type))
 			size = sizeof(void *);
 		else
@@ -3799,7 +3870,7 @@ static int btf_check_all_metas(struct btf_verifier_env *env)
 	cur = btf->nohdr_data + hdr->type_off;
 	end = cur + hdr->type_len;
 
-	env->log_type_id = 1;
+	env->log_type_id = btf->base_btf ? btf->start_id : 1;
 	while (cur < end) {
 		struct btf_type *t = cur;
 		s32 meta_size;
@@ -3826,8 +3897,8 @@ static bool btf_resolve_valid(struct btf_verifier_env *env,
 		return false;
 
 	if (btf_type_is_struct(t) || btf_type_is_datasec(t))
-		return !btf->resolved_ids[type_id] &&
-		       !btf->resolved_sizes[type_id];
+		return !btf_resolved_type_id(btf, type_id) &&
+		       !btf_resolved_type_size(btf, type_id);
 
 	if (btf_type_is_modifier(t) || btf_type_is_ptr(t) ||
 	    btf_type_is_var(t)) {
@@ -3847,7 +3918,7 @@ static bool btf_resolve_valid(struct btf_verifier_env *env,
 		elem_type = btf_type_id_size(btf, &elem_type_id, &elem_size);
 		return elem_type && !btf_type_is_modifier(elem_type) &&
 			(array->nelems * elem_size ==
-			 btf->resolved_sizes[type_id]);
+			 btf_resolved_type_size(btf, type_id));
 	}
 
 	return false;
@@ -3889,7 +3960,8 @@ static int btf_resolve(struct btf_verifier_env *env,
 static int btf_check_all_types(struct btf_verifier_env *env)
 {
 	struct btf *btf = env->btf;
-	u32 type_id;
+	const struct btf_type *t;
+	u32 type_id, i;
 	int err;
 
 	err = env_resolve_init(env);
@@ -3897,8 +3969,9 @@ static int btf_check_all_types(struct btf_verifier_env *env)
 		return err;
 
 	env->phase++;
-	for (type_id = 1; type_id <= btf->nr_types; type_id++) {
-		const struct btf_type *t = btf_type_by_id(btf, type_id);
+	for (i = btf->base_btf ? 0 : 1; i < btf->nr_types; i++) {
+		type_id = btf->start_id + i;
+		t = btf_type_by_id(btf, type_id);
 
 		env->log_type_id = type_id;
 		if (btf_type_needs_resolve(t) &&
@@ -3935,7 +4008,7 @@ static int btf_parse_type_sec(struct btf_verifier_env *env)
 		return -EINVAL;
 	}
 
-	if (!hdr->type_len) {
+	if (!env->btf->base_btf && !hdr->type_len) {
 		btf_verifier_log(env, "No type found");
 		return -EINVAL;
 	}
@@ -3962,13 +4035,18 @@ static int btf_parse_str_sec(struct btf_verifier_env *env)
 		return -EINVAL;
 	}
 
-	if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_NAME_OFFSET ||
-	    start[0] || end[-1]) {
+	btf->strings = start;
+
+	if (btf->base_btf && !hdr->str_len)
+		return 0;
+	if (!hdr->str_len || hdr->str_len - 1 > BTF_MAX_NAME_OFFSET || end[-1]) {
+		btf_verifier_log(env, "Invalid string section");
+		return -EINVAL;
+	}
+	if (!btf->base_btf && start[0]) {
 		btf_verifier_log(env, "Invalid string section");
 		return -EINVAL;
 	}
-
-	btf->strings = start;
 
 	return 0;
 }
@@ -4909,7 +4987,7 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
 	while (t && btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
 	if (!t) {
-		*bad_type = btf->types[0];
+		*bad_type = btf_type_by_id(btf, 0);
 		return -EINVAL;
 	}
 	if (btf_type_is_ptr(t))
-- 
2.24.1

[RFC PATCH bpf-next 2/5] bpf: assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ_INFO

[Andrii Nakryiko]

Allocate ID for vmlinux BTF. This makes it visible when iterating over all
BTF objects in the system. To allow distinguishing vmlinux BTF (and later
kernel module BTF) from user-provided BTFs, expose extra kernel_btf flag, as
well as BTF name (empty for vmlinux BTF, but will be used for kernel module
BTF). We might want to later allow specifying BTF name for user-provided BTFs
as well, if that makes sense. But currently this is reserved only for
in-kernel BTFs.

Having in-kernel BTFs exposed IDs will allow to extend BPF APIs that require
in-kernel BTF type with ability to specify BTF types from kernel modules, not
just vmlinux BTF. This will be implemented in a follow up patch set for
fentry/fexit/fmod_ret/lsm/etc.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 include/uapi/linux/bpf.h       |  3 +++
 kernel/bpf/btf.c               | 38 ++++++++++++++++++++++++++++++++--
 tools/include/uapi/linux/bpf.h |  3 +++
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e6ceac3f7d62..7955b144f267 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4418,6 +4418,9 @@ struct bpf_btf_info {
 	__aligned_u64 btf;
 	__u32 btf_size;
 	__u32 id;
+	__aligned_u64 name;
+	__u32 name_len;
+	__u32 kernel_btf;
 } __attribute__((aligned(8)));
 
 struct bpf_link_info {
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f61944a3873b..6a99677e57c0 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -215,6 +215,8 @@ struct btf {
 	struct btf *base_btf;
 	u32 start_id; /* first type ID in this BTF (0 for base BTF) */
 	u32 start_str_off; /* first string offset (0 for base BTF) */
+	char name[MODULE_NAME_LEN];
+	bool kernel_btf;
 };
 
 enum verifier_phase {
@@ -4441,6 +4443,7 @@ struct btf *btf_parse_vmlinux(void)
 
 	btf->data = __start_BTF;
 	btf->data_size = __stop_BTF - __start_BTF;
+	btf->kernel_btf = true;
 
 	err = btf_parse_hdr(env);
 	if (err)
@@ -4466,8 +4469,13 @@ struct btf *btf_parse_vmlinux(void)
 
 	bpf_struct_ops_init(btf, log);
 
-	btf_verifier_env_free(env);
 	refcount_set(&btf->refcnt, 1);
+
+	err = btf_alloc_id(btf);
+	if (err)
+		goto errout;
+
+	btf_verifier_env_free(env);
 	return btf;
 
 errout:
@@ -5565,7 +5573,8 @@ int btf_get_info_by_fd(const struct btf *btf,
 	struct bpf_btf_info info;
 	u32 info_copy, btf_copy;
 	void __user *ubtf;
-	u32 uinfo_len;
+	char __user *uname;
+	u32 uinfo_len, uname_len, name_len;
 
 	uinfo = u64_to_user_ptr(attr->info.info);
 	uinfo_len = attr->info.info_len;
@@ -5582,6 +5591,31 @@ int btf_get_info_by_fd(const struct btf *btf,
 		return -EFAULT;
 	info.btf_size = btf->data_size;
 
+	info.kernel_btf = btf->kernel_btf;
+
+	uname = u64_to_user_ptr(info.name);
+	uname_len = info.name_len;
+	if (!uname ^ !uname_len)
+		return -EINVAL;
+
+	name_len = strlen(btf->name);
+	info.name_len = name_len;
+
+	if (uname) {
+		if (uname_len >= name_len + 1) {
+			if (copy_to_user(uname, btf->name, name_len + 1))
+				return -EFAULT;
+		} else {
+			char zero = '\0';
+
+			if (copy_to_user(uname, btf->name, uname_len - 1))
+				return -EFAULT;
+			if (put_user(zero, uname + uname_len - 1))
+				return -EFAULT;
+			return -ENOSPC;
+		}
+	}
+
 	if (copy_to_user(uinfo, &info, info_copy) ||
 	    put_user(info_copy, &uattr->info.info_len))
 		return -EFAULT;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e6ceac3f7d62..7955b144f267 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4418,6 +4418,9 @@ struct bpf_btf_info {
 	__aligned_u64 btf;
 	__u32 btf_size;
 	__u32 id;
+	__aligned_u64 name;
+	__u32 name_len;
+	__u32 kernel_btf;
 } __attribute__((aligned(8)));
 
 struct bpf_link_info {
-- 
2.24.1

Re: [RFC PATCH bpf-next 2/5] bpf: assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ_INFO

[Alexei Starovoitov]

On Wed, Nov 04, 2020 at 08:51:37PM -0800, Andrii Nakryiko wrote:
> @@ -215,6 +215,8 @@ struct btf {
>  	struct btf *base_btf;
>  	u32 start_id; /* first type ID in this BTF (0 for base BTF) */
>  	u32 start_str_off; /* first string offset (0 for base BTF) */
> +	char name[MODULE_NAME_LEN];
> +	bool kernel_btf;
>  };
>  
>  enum verifier_phase {
> @@ -4441,6 +4443,7 @@ struct btf *btf_parse_vmlinux(void)
>  
>  	btf->data = __start_BTF;
>  	btf->data_size = __stop_BTF - __start_BTF;
> +	btf->kernel_btf = true;

imo it's a bit weird for vmlinux's BTF to be flagged as 'kernel_btf'
and empty name, but kernel module's BTFs will not be marked as kernel,
but will have a name.
I think it's more natural to make vmlinux and module's BTF with kernel_btf=true flag
and give "vmlinux" name to base kernel BTF.
If somebody creates a kernel module with "vmlinux" name we will have a conflict,
but that name is for human pretty printing only anyway, so I think it's fine.

Re: [RFC PATCH bpf-next 2/5] bpf: assign ID to vmlinux BTF and return extra info for BTF in GET_OBJ_INFO

[Andrii Nakryiko]

On Thu, Nov 5, 2020 at 7:19 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Nov 04, 2020 at 08:51:37PM -0800, Andrii Nakryiko wrote:
> > @@ -215,6 +215,8 @@ struct btf {
> >       struct btf *base_btf;
> >       u32 start_id; /* first type ID in this BTF (0 for base BTF) */
> >       u32 start_str_off; /* first string offset (0 for base BTF) */
> > +     char name[MODULE_NAME_LEN];
> > +     bool kernel_btf;
> >  };
> >
> >  enum verifier_phase {
> > @@ -4441,6 +4443,7 @@ struct btf *btf_parse_vmlinux(void)
> >
> >       btf->data = __start_BTF;
> >       btf->data_size = __stop_BTF - __start_BTF;
> > +     btf->kernel_btf = true;
>
> imo it's a bit weird for vmlinux's BTF to be flagged as 'kernel_btf'
> and empty name, but kernel module's BTFs will not be marked as kernel,
> but will have a name.

module's BTF also has kernel_btf = true, see patch 4; would be weird otherwise

> I think it's more natural to make vmlinux and module's BTF with kernel_btf=true flag
> and give "vmlinux" name to base kernel BTF.

Yeah, I was wondering if I should name vmlinux BTF as "vmlinux"
explicitly, for whatever reason I decided to go with an empty name.
But I think it's not a bad idea to give it an explicit "vmlinux" name.
I'll do that in the next version. Will make bpftool logic more
straightforward as well.


> If somebody creates a kernel module with "vmlinux" name we will have a conflict,
> but that name is for human pretty printing only anyway, so I think it's fine.

yep.

[RFC PATCH bpf-next 3/5] kbuild: Add CONFIG_DEBUG_INFO_BTF_MODULES option or module BTFs

[Andrii Nakryiko]

Add Kconfig option to generate kernel module split BTFs, if pahole's version
support it. Kernel module BTF has to be re-grenerated if either vmlinux's BTF
changes or .ko changes. To achieve that, I needed a helper similar to
if_changed, but that would allow to filter out vmlinux from the list of
updated dependencies for .ko building. I've put it next to the only place that
uses and needs it, but it might be a better idea to just add it along the
other if_changed variants into scripts/Kbuild.include.

Each kernel module's BTF deduplication is pretty fast, as it does only
incremental BTF deduplication on top of already deduplicated vmlinux BTF. To
show the added build time, I've first ran make only just built kernel (to
establish the baseline) and then forced only BTF re-generation, without
regenerating .ko files. The build was performed with -j60 parallelization on
56-core machine. The final time also includes bzImage building, so it's not
a pure BTF overhead.

$ time make -j60
...
make -j60  27.65s user 10.96s system 782% cpu 4.933 total
$ touch ~/linux-build/default/vmlinux && time make -j60
...
make -j60  123.69s user 27.85s system 1566% cpu 9.675 total

So 4.6 seconds real time, with noticeable part spent in compressed vmlinux and
bzImage building.

To show size savings, I've built my kernel configuration with about 700 kernel
modules with full BTF per each kernel module (without deduplicating against
vmlinux) and with split BTF against deduplicated vmlinux (approach in this
patch). Below are top 10 modules with biggest BTF sizes. And total size of BTF
data across all kernel modules.

It shows that split BTF "compresses" 115MB down to 5MB total. And the biggest
kernel modules get a downsize from 500-570KB down to 200-300KB.

FULL BTF
========

$ for f in $(find . -name '*.ko'); do size -A -d $f | grep BTF | awk '{print $2}'; done | awk '{ s += $1 } END { print s }'
115710691

$ for f in $(find . -name '*.ko'); do printf "%s %d\n" $f $(size -A -d $f | grep BTF | awk '{print $2}'); done | sort -nr -k2 | head -n10
./drivers/gpu/drm/i915/i915.ko 570570
./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko 520240
./drivers/gpu/drm/radeon/radeon.ko 503849
./drivers/infiniband/hw/mlx5/mlx5_ib.ko 491777
./fs/xfs/xfs.ko 411544
./drivers/net/ethernet/intel/i40e/i40e.ko 403904
./drivers/net/ethernet/broadcom/bnx2x/bnx2x.ko 398754
./drivers/infiniband/core/ib_core.ko 397224
./fs/cifs/cifs.ko 386249
./fs/nfsd/nfsd.ko 379738

SPLIT BTF
=========

$ for f in $(find . -name '*.ko'); do size -A -d $f | grep BTF | awk '{print $2}'; done | awk '{ s += $1 } END { print s }'
5194047

$ for f in $(find . -name '*.ko'); do printf "%s %d\n" $f $(size -A -d $f | grep BTF | awk '{print $2}'); done | sort -nr -k2 | head -n10
./drivers/gpu/drm/i915/i915.ko 293206
./drivers/gpu/drm/radeon/radeon.ko 282103
./fs/xfs/xfs.ko 222150
./drivers/net/ethernet/mellanox/mlx5/core/mlx5_core.ko 198503
./drivers/infiniband/hw/mlx5/mlx5_ib.ko 198356
./drivers/net/ethernet/broadcom/bnx2x/bnx2x.ko 113444
./fs/cifs/cifs.ko 109379
./arch/x86/kvm/kvm.ko 100225
./drivers/gpu/drm/drm.ko 94827
./drivers/infiniband/core/ib_core.ko 91188

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 lib/Kconfig.debug         | 10 ++++++++++
 scripts/Makefile.modfinal | 20 ++++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index d7a7bc3b6098..d3303ed58ff0 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -265,6 +265,9 @@ config DEBUG_INFO_DWARF4
 	  But it significantly improves the success of resolving
 	  variables in gdb on optimized code.
 
+config PAHOLE_HAS_SPLIT_BTF
+	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
+
 config DEBUG_INFO_BTF
 	bool "Generate BTF typeinfo"
 	depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
@@ -274,6 +277,13 @@ config DEBUG_INFO_BTF
 	  Turning this on expects presence of pahole tool, which will convert
 	  DWARF type info into equivalent deduplicated BTF type info.
 
+config DEBUG_INFO_BTF_MODULES
+	bool "Generate BTF for kernel modules"
+	def_bool y
+	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
+	help
+	  Generate compact split BTF type information for kernel modules.
+
 config GDB_SCRIPTS
 	bool "Provide GDB scripts for kernel debugging"
 	help
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index ae01baf96f4e..02b892421f7a 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -6,6 +6,7 @@
 PHONY := __modfinal
 __modfinal:
 
+include include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
 
 # for c_flags
@@ -36,8 +37,23 @@ quiet_cmd_ld_ko_o = LD [M]  $@
 		-T scripts/module.lds -o $@ $(filter %.o, $^);		\
 	$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
 
-$(modules): %.ko: %.o %.mod.o scripts/module.lds FORCE
-	+$(call if_changed,ld_ko_o)
+quiet_cmd_btf_ko = BTF [M] $@
+      cmd_btf_ko = LLVM_OBJCOPY=$(OBJCOPY) $(PAHOLE) -J --btf_base vmlinux $@
+
+# Same as newer-prereqs, but allows to exclude specified extra dependencies
+newer_prereqs_except = $(filter-out $(PHONY) $(1),$?)
+
+# Same as if_changed, but allows to exclude specified extra dependencies
+if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
+	$(cmd);                                                              \
+	printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
+
+# Re-generate module BTFs if either module's .ko or vmlinux changed
+$(modules): %.ko: %.o %.mod.o scripts/module.lds vmlinux FORCE
+	+$(call if_changed_except,ld_ko_o,vmlinux)
+ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	+$(if $(newer-prereqs),$(call cmd,btf_ko))
+endif
 
 targets += $(modules) $(modules:.ko=.mod.o)
 
-- 
2.24.1

Re: [RFC PATCH bpf-next 3/5] kbuild: Add CONFIG_DEBUG_INFO_BTF_MODULES option or module BTFs

[Alexei Starovoitov]

On Wed, Nov 04, 2020 at 08:51:38PM -0800, Andrii Nakryiko wrote:
>  
> +config DEBUG_INFO_BTF_MODULES
> +	bool "Generate BTF for kernel modules"
> +	def_bool y
> +	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF

Does it need to be a new config ?
Can the build ran pahole if DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF ?

Re: [RFC PATCH bpf-next 3/5] kbuild: Add CONFIG_DEBUG_INFO_BTF_MODULES option or module BTFs

[Andrii Nakryiko]

On Thu, Nov 5, 2020 at 7:13 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Nov 04, 2020 at 08:51:38PM -0800, Andrii Nakryiko wrote:
> >
> > +config DEBUG_INFO_BTF_MODULES
> > +     bool "Generate BTF for kernel modules"
> > +     def_bool y
> > +     depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
>
> Does it need to be a new config ?
> Can the build ran pahole if DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF ?

It probably doesn't. If I drop the "bool" line, it will become
non-configurable calculated Kconfig value, convenient to use
everywhere. All the rest will stay exactly the same. It's nice to not
have to do "if defined(DEBUG_INFO_BTF) && defined(MODULES) &&
defined(PAHOLE_HAS_SPLIT_BTF)" checks, but rather a simple "ifdef
CONFIG_DEBUG_INFO_BTF_MODULES". Does that work?

Re: [RFC PATCH bpf-next 3/5] kbuild: Add CONFIG_DEBUG_INFO_BTF_MODULES option or module BTFs

[Alexei Starovoitov]

On Thu, Nov 5, 2020 at 7:48 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Thu, Nov 5, 2020 at 7:13 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Nov 04, 2020 at 08:51:38PM -0800, Andrii Nakryiko wrote:
> > >
> > > +config DEBUG_INFO_BTF_MODULES
> > > +     bool "Generate BTF for kernel modules"
> > > +     def_bool y
> > > +     depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> >
> > Does it need to be a new config ?
> > Can the build ran pahole if DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF ?
>
> It probably doesn't. If I drop the "bool" line, it will become
> non-configurable calculated Kconfig value, convenient to use
> everywhere. All the rest will stay exactly the same. It's nice to not
> have to do "if defined(DEBUG_INFO_BTF) && defined(MODULES) &&
> defined(PAHOLE_HAS_SPLIT_BTF)" checks, but rather a simple "ifdef
> CONFIG_DEBUG_INFO_BTF_MODULES". Does that work?

Makes sense.

[RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

[Andrii Nakryiko]

Add kernel module listener that will load/validate and unload module BTF.
Module BTFs gets ID generated for them, which makes it possible to iterate
them with existing BTF iteration API. They are given their respective module's
names, which will get reported through GET_OBJ_INFO API. They are also marked
as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.

Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
tools to inspect module BTF contents and dump their types with existing tools:

[vmuser@archvm bpf]$ ls -la /sys/kernel/btf
total 0
drwxr-xr-x  2 root root       0 Nov  4 19:46 .
drwxr-xr-x 13 root root       0 Nov  4 19:46 ..

...

-r--r--r--  1 root root     888 Nov  4 19:46 irqbypass
-r--r--r--  1 root root  100225 Nov  4 19:46 kvm
-r--r--r--  1 root root   35401 Nov  4 19:46 kvm_intel
-r--r--r--  1 root root     120 Nov  4 19:46 pcspkr
-r--r--r--  1 root root     399 Nov  4 19:46 serio_raw
-r--r--r--  1 root root 4094095 Nov  4 19:46 vmlinux

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 include/linux/bpf.h    |   2 +
 include/linux/module.h |   4 +
 kernel/bpf/btf.c       | 193 +++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/sysfs_btf.c |   2 +-
 kernel/module.c        |  32 +++++++
 5 files changed, 232 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 2fffd30e13ac..3cb89cd7177b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -36,9 +36,11 @@ struct seq_operations;
 struct bpf_iter_aux_info;
 struct bpf_local_storage;
 struct bpf_local_storage_map;
+struct kobject;
 
 extern struct idr btf_idr;
 extern spinlock_t btf_idr_lock;
+extern struct kobject *btf_kobj;
 
 typedef int (*bpf_iter_init_seq_priv_t)(void *private_data,
 					struct bpf_iter_aux_info *aux);
diff --git a/include/linux/module.h b/include/linux/module.h
index a29187f7c360..20fce258ffba 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -475,6 +475,10 @@ struct module {
 	unsigned int num_bpf_raw_events;
 	struct bpf_raw_event_map *bpf_raw_events;
 #endif
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	unsigned int btf_data_size;
+	void *btf_data;
+#endif
 #ifdef CONFIG_JUMP_LABEL
 	struct jump_entry *jump_entries;
 	unsigned int num_jump_entries;
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 6a99677e57c0..475d1b95b3d8 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -23,6 +23,8 @@
 #include <linux/perf_event.h>
 #include <linux/bsearch.h>
 #include <linux/btf_ids.h>
+#include <linux/kobject.h>
+#include <linux/sysfs.h>
 #include <net/sock.h>
 
 /* BTF (BPF Type Format) is the meta data format which describes
@@ -4487,6 +4489,75 @@ struct btf *btf_parse_vmlinux(void)
 	return ERR_PTR(err);
 }
 
+static struct btf *btf_parse_module(const char *module_name, const void *data, unsigned int data_size)
+{
+	struct btf_verifier_env *env = NULL;
+	struct bpf_verifier_log *log;
+	struct btf *btf = NULL, *base_btf;
+	int err;
+
+	base_btf = bpf_get_btf_vmlinux();
+	if (IS_ERR(base_btf))
+		return base_btf;
+	if (!base_btf)
+		return ERR_PTR(-EINVAL);
+
+	env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
+	if (!env)
+		return ERR_PTR(-ENOMEM);
+
+	log = &env->log;
+	log->level = BPF_LOG_KERNEL;
+
+	btf = kzalloc(sizeof(*btf), GFP_KERNEL | __GFP_NOWARN);
+	if (!btf) {
+		err = -ENOMEM;
+		goto errout;
+	}
+	env->btf = btf;
+
+	btf->base_btf = base_btf;
+	btf->start_id = base_btf->nr_types;
+	btf->start_str_off = base_btf->hdr.str_len;
+	btf->kernel_btf = true;
+	snprintf(btf->name, sizeof(btf->name), "%s", module_name);
+
+	btf->data = kvmalloc(data_size, GFP_KERNEL | __GFP_NOWARN);
+	if (!btf->data) {
+		err = -ENOMEM;
+		goto errout;
+	}
+	memcpy(btf->data, data, data_size);
+	btf->data_size = data_size;
+
+	err = btf_parse_hdr(env);
+	if (err)
+		goto errout;
+
+	btf->nohdr_data = btf->data + btf->hdr.hdr_len;
+
+	err = btf_parse_str_sec(env);
+	if (err)
+		goto errout;
+
+	err = btf_check_all_metas(env);
+	if (err)
+		goto errout;
+
+	btf_verifier_env_free(env);
+	refcount_set(&btf->refcnt, 1);
+	return btf;
+
+errout:
+	btf_verifier_env_free(env);
+	if (btf) {
+		kvfree(btf->data);
+		kvfree(btf->types);
+		kfree(btf);
+	}
+	return ERR_PTR(err);
+}
+
 struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog)
 {
 	struct bpf_prog *tgt_prog = prog->aux->dst_prog;
@@ -5660,3 +5731,125 @@ bool btf_id_set_contains(const struct btf_id_set *set, u32 id)
 {
 	return bsearch(&id, set->ids, set->cnt, sizeof(u32), btf_id_cmp_func) != NULL;
 }
+
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+struct btf_module {
+	struct list_head list;
+	struct module *module;
+	struct btf *btf;
+	struct bin_attribute *sysfs_attr;
+};
+
+static LIST_HEAD(btf_modules);
+static DEFINE_MUTEX(btf_module_mutex);
+
+static ssize_t
+btf_module_read(struct file *file, struct kobject *kobj,
+		struct bin_attribute *bin_attr,
+		char *buf, loff_t off, size_t len)
+{
+	const struct btf *btf = bin_attr->private;
+
+	memcpy(buf, btf->data + off, len);
+	return len;
+}
+
+static int btf_module_notify(struct notifier_block *nb, unsigned long op,
+			     void *module)
+{
+	struct btf_module *btf_mod, *tmp;
+	struct module *mod = module;
+	struct btf *btf;
+	int err = 0;
+
+	if (mod->btf_data_size == 0 ||
+	    (op != MODULE_STATE_COMING && op != MODULE_STATE_GOING))
+		goto out;
+
+	switch (op) {
+	case MODULE_STATE_COMING:
+		btf_mod = kzalloc(sizeof(*btf_mod), GFP_KERNEL);
+		if (!btf_mod) {
+			err = -ENOMEM;
+			goto out;
+		}
+		btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size);
+		if (IS_ERR(btf)) {
+			kfree(btf_mod);
+			err = PTR_ERR(btf);
+			goto out;
+		}
+		err = btf_alloc_id(btf);
+		if (err) {
+			btf_free(btf);
+			kfree(btf_mod);
+			goto out;
+		}
+
+		mutex_lock(&btf_module_mutex);
+		btf_mod->module = module;
+		btf_mod->btf = btf;
+		list_add(&btf_mod->list, &btf_modules);
+		mutex_unlock(&btf_module_mutex);
+
+		if (IS_ENABLED(CONFIG_SYSFS)) {
+			struct bin_attribute *attr;
+
+			attr = kzalloc(sizeof(*attr), GFP_KERNEL);
+			if (!attr) {
+				WARN(1, "failed to register module [%s] BTF in sysfs\n", mod->name);
+				goto out;
+			}
+
+			attr->attr.name = btf->name;
+			attr->attr.mode = 0444;
+			attr->size = btf->data_size;
+			attr->private = btf;
+			attr->read = btf_module_read;
+
+			err = sysfs_create_bin_file(btf_kobj, attr);
+			if (err) {
+				kfree(attr);
+				WARN(1, "failed to register module [%s] BTF in sysfs: %d\n",
+				     mod->name, err);
+				err = 0;
+				goto out;
+			}
+
+			btf_mod->sysfs_attr = attr;
+		}
+
+		break;
+	case MODULE_STATE_GOING:
+		mutex_lock(&btf_module_mutex);
+		list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
+			if (btf_mod->module != module)
+				continue;
+
+			list_del(&btf_mod->list);
+			if (btf_mod->sysfs_attr)
+				sysfs_remove_bin_file(btf_kobj, btf_mod->sysfs_attr);
+			btf_put(btf_mod->btf);
+			kfree(btf_mod->sysfs_attr);
+			kfree(btf_mod);
+			break;
+		}
+		mutex_unlock(&btf_module_mutex);
+		break;
+	}
+out:
+	return notifier_from_errno(err);
+}
+
+static struct notifier_block btf_module_nb = {
+	.notifier_call = btf_module_notify,
+};
+
+static int __init btf_module_init(void)
+{
+	register_module_notifier(&btf_module_nb);
+	return 0;
+}
+
+fs_initcall(btf_module_init);
+#endif /* CONFIG_DEBUG_INFO_BTF_MODULES */
diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index 11b3380887fa..ef6911aee3bb 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -26,7 +26,7 @@ static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
 	.read = btf_vmlinux_read,
 };
 
-static struct kobject *btf_kobj;
+struct kobject *btf_kobj;
 
 static int __init btf_vmlinux_init(void)
 {
diff --git a/kernel/module.c b/kernel/module.c
index a4fa44a652a7..af71fc53eb25 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -380,6 +380,35 @@ static void *section_objs(const struct load_info *info,
 	return (void *)info->sechdrs[sec].sh_addr;
 }
 
+/* Find a module section: 0 means not found. Ignores SHF_ALLOC flag. */
+static unsigned int find_any_sec(const struct load_info *info, const char *name)
+{
+	unsigned int i;
+
+	for (i = 1; i < info->hdr->e_shnum; i++) {
+		Elf_Shdr *shdr = &info->sechdrs[i];
+		if (strcmp(info->secstrings + shdr->sh_name, name) == 0)
+			return i;
+	}
+	return 0;
+}
+
+/*
+ * Find a module section, or NULL. Fill in number of "objects" in section.
+ * Ignores SHF_ALLOC flag.
+ */
+static void *any_section_objs(const struct load_info *info,
+			      const char *name,
+			      size_t object_size,
+			      unsigned int *num)
+{
+	unsigned int sec = find_any_sec(info, name);
+
+	/* Section 0 has sh_addr 0 and sh_size 0. */
+	*num = info->sechdrs[sec].sh_size / object_size;
+	return (void *)info->sechdrs[sec].sh_addr;
+}
+
 /* Provided by the linker */
 extern const struct kernel_symbol __start___ksymtab[];
 extern const struct kernel_symbol __stop___ksymtab[];
@@ -3250,6 +3279,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 					   sizeof(*mod->bpf_raw_events),
 					   &mod->num_bpf_raw_events);
 #endif
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	mod->btf_data = any_section_objs(info, ".BTF", 1, &mod->btf_data_size);
+#endif
 #ifdef CONFIG_JUMP_LABEL
 	mod->jump_entries = section_objs(info, "__jump_table",
 					sizeof(*mod->jump_entries),
-- 
2.24.1

Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

[Jakub Kicinski]

On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:
> Add kernel module listener that will load/validate and unload module BTF.
> Module BTFs gets ID generated for them, which makes it possible to iterate
> them with existing BTF iteration API. They are given their respective module's
> names, which will get reported through GET_OBJ_INFO API. They are also marked
> as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
> 
> Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> tools to inspect module BTF contents and dump their types with existing tools:

Is there any precedent for creating per-module files under a new
sysfs directory structure? My intuition would be that these files 
belong under /sys/module/

Also the CC list on these patches is quite narrow. You should have 
at least CCed the module maintainer. Adding some folks now.

> [vmuser@archvm bpf]$ ls -la /sys/kernel/btf
> total 0
> drwxr-xr-x  2 root root       0 Nov  4 19:46 .
> drwxr-xr-x 13 root root       0 Nov  4 19:46 ..
> 
> ...
> 
> -r--r--r--  1 root root     888 Nov  4 19:46 irqbypass
> -r--r--r--  1 root root  100225 Nov  4 19:46 kvm
> -r--r--r--  1 root root   35401 Nov  4 19:46 kvm_intel
> -r--r--r--  1 root root     120 Nov  4 19:46 pcspkr
> -r--r--r--  1 root root     399 Nov  4 19:46 serio_raw
> -r--r--r--  1 root root 4094095 Nov  4 19:46 vmlinux
> 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  include/linux/bpf.h    |   2 +
>  include/linux/module.h |   4 +
>  kernel/bpf/btf.c       | 193 +++++++++++++++++++++++++++++++++++++++++
>  kernel/bpf/sysfs_btf.c |   2 +-
>  kernel/module.c        |  32 +++++++
>  5 files changed, 232 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2fffd30e13ac..3cb89cd7177b 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -36,9 +36,11 @@ struct seq_operations;
>  struct bpf_iter_aux_info;
>  struct bpf_local_storage;
>  struct bpf_local_storage_map;
> +struct kobject;
>  
>  extern struct idr btf_idr;
>  extern spinlock_t btf_idr_lock;
> +extern struct kobject *btf_kobj;
>  
>  typedef int (*bpf_iter_init_seq_priv_t)(void *private_data,
>  					struct bpf_iter_aux_info *aux);
> diff --git a/include/linux/module.h b/include/linux/module.h
> index a29187f7c360..20fce258ffba 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -475,6 +475,10 @@ struct module {
>  	unsigned int num_bpf_raw_events;
>  	struct bpf_raw_event_map *bpf_raw_events;
>  #endif
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	unsigned int btf_data_size;
> +	void *btf_data;
> +#endif
>  #ifdef CONFIG_JUMP_LABEL
>  	struct jump_entry *jump_entries;
>  	unsigned int num_jump_entries;
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 6a99677e57c0..475d1b95b3d8 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -23,6 +23,8 @@
>  #include <linux/perf_event.h>
>  #include <linux/bsearch.h>
>  #include <linux/btf_ids.h>
> +#include <linux/kobject.h>
> +#include <linux/sysfs.h>
>  #include <net/sock.h>
>  
>  /* BTF (BPF Type Format) is the meta data format which describes
> @@ -4487,6 +4489,75 @@ struct btf *btf_parse_vmlinux(void)
>  	return ERR_PTR(err);
>  }
>  
> +static struct btf *btf_parse_module(const char *module_name, const void *data, unsigned int data_size)
> +{
> +	struct btf_verifier_env *env = NULL;
> +	struct bpf_verifier_log *log;
> +	struct btf *btf = NULL, *base_btf;
> +	int err;
> +
> +	base_btf = bpf_get_btf_vmlinux();
> +	if (IS_ERR(base_btf))
> +		return base_btf;
> +	if (!base_btf)
> +		return ERR_PTR(-EINVAL);
> +
> +	env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
> +	if (!env)
> +		return ERR_PTR(-ENOMEM);
> +
> +	log = &env->log;
> +	log->level = BPF_LOG_KERNEL;
> +
> +	btf = kzalloc(sizeof(*btf), GFP_KERNEL | __GFP_NOWARN);
> +	if (!btf) {
> +		err = -ENOMEM;
> +		goto errout;
> +	}
> +	env->btf = btf;
> +
> +	btf->base_btf = base_btf;
> +	btf->start_id = base_btf->nr_types;
> +	btf->start_str_off = base_btf->hdr.str_len;
> +	btf->kernel_btf = true;
> +	snprintf(btf->name, sizeof(btf->name), "%s", module_name);
> +
> +	btf->data = kvmalloc(data_size, GFP_KERNEL | __GFP_NOWARN);
> +	if (!btf->data) {
> +		err = -ENOMEM;
> +		goto errout;
> +	}
> +	memcpy(btf->data, data, data_size);
> +	btf->data_size = data_size;
> +
> +	err = btf_parse_hdr(env);
> +	if (err)
> +		goto errout;
> +
> +	btf->nohdr_data = btf->data + btf->hdr.hdr_len;
> +
> +	err = btf_parse_str_sec(env);
> +	if (err)
> +		goto errout;
> +
> +	err = btf_check_all_metas(env);
> +	if (err)
> +		goto errout;
> +
> +	btf_verifier_env_free(env);
> +	refcount_set(&btf->refcnt, 1);
> +	return btf;
> +
> +errout:
> +	btf_verifier_env_free(env);
> +	if (btf) {
> +		kvfree(btf->data);
> +		kvfree(btf->types);
> +		kfree(btf);
> +	}
> +	return ERR_PTR(err);
> +}
> +
>  struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog)
>  {
>  	struct bpf_prog *tgt_prog = prog->aux->dst_prog;
> @@ -5660,3 +5731,125 @@ bool btf_id_set_contains(const struct btf_id_set *set, u32 id)
>  {
>  	return bsearch(&id, set->ids, set->cnt, sizeof(u32), btf_id_cmp_func) != NULL;
>  }
> +
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +struct btf_module {
> +	struct list_head list;
> +	struct module *module;
> +	struct btf *btf;
> +	struct bin_attribute *sysfs_attr;
> +};
> +
> +static LIST_HEAD(btf_modules);
> +static DEFINE_MUTEX(btf_module_mutex);
> +
> +static ssize_t
> +btf_module_read(struct file *file, struct kobject *kobj,
> +		struct bin_attribute *bin_attr,
> +		char *buf, loff_t off, size_t len)
> +{
> +	const struct btf *btf = bin_attr->private;
> +
> +	memcpy(buf, btf->data + off, len);
> +	return len;
> +}
> +
> +static int btf_module_notify(struct notifier_block *nb, unsigned long op,
> +			     void *module)
> +{
> +	struct btf_module *btf_mod, *tmp;
> +	struct module *mod = module;
> +	struct btf *btf;
> +	int err = 0;
> +
> +	if (mod->btf_data_size == 0 ||
> +	    (op != MODULE_STATE_COMING && op != MODULE_STATE_GOING))
> +		goto out;
> +
> +	switch (op) {
> +	case MODULE_STATE_COMING:
> +		btf_mod = kzalloc(sizeof(*btf_mod), GFP_KERNEL);
> +		if (!btf_mod) {
> +			err = -ENOMEM;
> +			goto out;
> +		}
> +		btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size);
> +		if (IS_ERR(btf)) {
> +			kfree(btf_mod);
> +			err = PTR_ERR(btf);
> +			goto out;
> +		}
> +		err = btf_alloc_id(btf);
> +		if (err) {
> +			btf_free(btf);
> +			kfree(btf_mod);
> +			goto out;
> +		}
> +
> +		mutex_lock(&btf_module_mutex);
> +		btf_mod->module = module;
> +		btf_mod->btf = btf;
> +		list_add(&btf_mod->list, &btf_modules);
> +		mutex_unlock(&btf_module_mutex);
> +
> +		if (IS_ENABLED(CONFIG_SYSFS)) {
> +			struct bin_attribute *attr;
> +
> +			attr = kzalloc(sizeof(*attr), GFP_KERNEL);
> +			if (!attr) {
> +				WARN(1, "failed to register module [%s] BTF in sysfs\n", mod->name);
> +				goto out;
> +			}
> +
> +			attr->attr.name = btf->name;
> +			attr->attr.mode = 0444;
> +			attr->size = btf->data_size;
> +			attr->private = btf;
> +			attr->read = btf_module_read;
> +
> +			err = sysfs_create_bin_file(btf_kobj, attr);
> +			if (err) {
> +				kfree(attr);
> +				WARN(1, "failed to register module [%s] BTF in sysfs: %d\n",
> +				     mod->name, err);
> +				err = 0;
> +				goto out;
> +			}
> +
> +			btf_mod->sysfs_attr = attr;
> +		}
> +
> +		break;
> +	case MODULE_STATE_GOING:
> +		mutex_lock(&btf_module_mutex);
> +		list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
> +			if (btf_mod->module != module)
> +				continue;
> +
> +			list_del(&btf_mod->list);
> +			if (btf_mod->sysfs_attr)
> +				sysfs_remove_bin_file(btf_kobj, btf_mod->sysfs_attr);
> +			btf_put(btf_mod->btf);
> +			kfree(btf_mod->sysfs_attr);
> +			kfree(btf_mod);
> +			break;
> +		}
> +		mutex_unlock(&btf_module_mutex);
> +		break;
> +	}
> +out:
> +	return notifier_from_errno(err);
> +}
> +
> +static struct notifier_block btf_module_nb = {
> +	.notifier_call = btf_module_notify,
> +};
> +
> +static int __init btf_module_init(void)
> +{
> +	register_module_notifier(&btf_module_nb);
> +	return 0;
> +}
> +
> +fs_initcall(btf_module_init);
> +#endif /* CONFIG_DEBUG_INFO_BTF_MODULES */
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index 11b3380887fa..ef6911aee3bb 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -26,7 +26,7 @@ static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
>  	.read = btf_vmlinux_read,
>  };
>  
> -static struct kobject *btf_kobj;
> +struct kobject *btf_kobj;
>  
>  static int __init btf_vmlinux_init(void)
>  {
> diff --git a/kernel/module.c b/kernel/module.c
> index a4fa44a652a7..af71fc53eb25 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -380,6 +380,35 @@ static void *section_objs(const struct load_info *info,
>  	return (void *)info->sechdrs[sec].sh_addr;
>  }
>  
> +/* Find a module section: 0 means not found. Ignores SHF_ALLOC flag. */
> +static unsigned int find_any_sec(const struct load_info *info, const char *name)
> +{
> +	unsigned int i;
> +
> +	for (i = 1; i < info->hdr->e_shnum; i++) {
> +		Elf_Shdr *shdr = &info->sechdrs[i];
> +		if (strcmp(info->secstrings + shdr->sh_name, name) == 0)
> +			return i;
> +	}
> +	return 0;
> +}
> +
> +/*
> + * Find a module section, or NULL. Fill in number of "objects" in section.
> + * Ignores SHF_ALLOC flag.
> + */
> +static void *any_section_objs(const struct load_info *info,
> +			      const char *name,
> +			      size_t object_size,
> +			      unsigned int *num)
> +{
> +	unsigned int sec = find_any_sec(info, name);
> +
> +	/* Section 0 has sh_addr 0 and sh_size 0. */
> +	*num = info->sechdrs[sec].sh_size / object_size;
> +	return (void *)info->sechdrs[sec].sh_addr;
> +}
> +
>  /* Provided by the linker */
>  extern const struct kernel_symbol __start___ksymtab[];
>  extern const struct kernel_symbol __stop___ksymtab[];
> @@ -3250,6 +3279,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
>  					   sizeof(*mod->bpf_raw_events),
>  					   &mod->num_bpf_raw_events);
>  #endif
> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> +	mod->btf_data = any_section_objs(info, ".BTF", 1, &mod->btf_data_size);
> +#endif
>  #ifdef CONFIG_JUMP_LABEL
>  	mod->jump_entries = section_objs(info, "__jump_table",
>  					sizeof(*mod->jump_entries),

Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

[Greg Kroah-Hartman]

On Thu, Nov 05, 2020 at 08:39:25AM -0800, Jakub Kicinski wrote:
> On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:
> > Add kernel module listener that will load/validate and unload module BTF.
> > Module BTFs gets ID generated for them, which makes it possible to iterate
> > them with existing BTF iteration API. They are given their respective module's
> > names, which will get reported through GET_OBJ_INFO API. They are also marked
> > as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
> > 
> > Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> > sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> > tools to inspect module BTF contents and dump their types with existing tools:
> 
> Is there any precedent for creating per-module files under a new
> sysfs directory structure? My intuition would be that these files 
> belong under /sys/module/

Ick, why?  What's wrong with them under btf?  The module core code
"owns" the /sys/modules/ tree.  If you want others to mess with that, it
will get tricky.


> Also the CC list on these patches is quite narrow. You should have 
> at least CCed the module maintainer. Adding some folks now.
> 
> > [vmuser@archvm bpf]$ ls -la /sys/kernel/btf
> > total 0
> > drwxr-xr-x  2 root root       0 Nov  4 19:46 .
> > drwxr-xr-x 13 root root       0 Nov  4 19:46 ..
> > 
> > ...
> > 
> > -r--r--r--  1 root root     888 Nov  4 19:46 irqbypass
> > -r--r--r--  1 root root  100225 Nov  4 19:46 kvm
> > -r--r--r--  1 root root   35401 Nov  4 19:46 kvm_intel
> > -r--r--r--  1 root root     120 Nov  4 19:46 pcspkr
> > -r--r--r--  1 root root     399 Nov  4 19:46 serio_raw
> > -r--r--r--  1 root root 4094095 Nov  4 19:46 vmlinux
> > 
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > ---
> >  include/linux/bpf.h    |   2 +
> >  include/linux/module.h |   4 +
> >  kernel/bpf/btf.c       | 193 +++++++++++++++++++++++++++++++++++++++++
> >  kernel/bpf/sysfs_btf.c |   2 +-
> >  kernel/module.c        |  32 +++++++
> >  5 files changed, 232 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 2fffd30e13ac..3cb89cd7177b 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -36,9 +36,11 @@ struct seq_operations;
> >  struct bpf_iter_aux_info;
> >  struct bpf_local_storage;
> >  struct bpf_local_storage_map;
> > +struct kobject;
> >  
> >  extern struct idr btf_idr;
> >  extern spinlock_t btf_idr_lock;
> > +extern struct kobject *btf_kobj;

I don't see any Documentation/ABI/ updates for the sysfs changes here,
did I miss it?

thanks,

greg k-h

Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

[Jakub Kicinski]

On Thu, 5 Nov 2020 17:46:16 +0100 Greg Kroah-Hartman wrote:
> On Thu, Nov 05, 2020 at 08:39:25AM -0800, Jakub Kicinski wrote:
> > On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:  
> > > Add kernel module listener that will load/validate and unload module BTF.
> > > Module BTFs gets ID generated for them, which makes it possible to iterate
> > > them with existing BTF iteration API. They are given their respective module's
> > > names, which will get reported through GET_OBJ_INFO API. They are also marked
> > > as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
> > > 
> > > Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> > > sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> > > tools to inspect module BTF contents and dump their types with existing tools:  
> > 
> > Is there any precedent for creating per-module files under a new
> > sysfs directory structure? My intuition would be that these files 
> > belong under /sys/module/  
> 
> Ick, why?  What's wrong with them under btf?  The module core code
> "owns" the /sys/modules/ tree.  If you want others to mess with that, 
> it will get tricky.

It's debug info, that's where I would look for it. 

Clearly I'd be wrong to do so :)

Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

[Andrii Nakryiko]

On Thu, Nov 5, 2020 at 8:45 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Thu, Nov 05, 2020 at 08:39:25AM -0800, Jakub Kicinski wrote:
> > On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:
> > > Add kernel module listener that will load/validate and unload module BTF.
> > > Module BTFs gets ID generated for them, which makes it possible to iterate
> > > them with existing BTF iteration API. They are given their respective module's
> > > names, which will get reported through GET_OBJ_INFO API. They are also marked
> > > as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
> > >
> > > Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> > > sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> > > tools to inspect module BTF contents and dump their types with existing tools:
> >
> > Is there any precedent for creating per-module files under a new
> > sysfs directory structure? My intuition would be that these files
> > belong under /sys/module/
>
> Ick, why?  What's wrong with them under btf?  The module core code
> "owns" the /sys/modules/ tree.  If you want others to mess with that, it
> will get tricky.
>
>
> > Also the CC list on these patches is quite narrow. You should have
> > at least CCed the module maintainer. Adding some folks now.
> >
> > > [vmuser@archvm bpf]$ ls -la /sys/kernel/btf
> > > total 0
> > > drwxr-xr-x  2 root root       0 Nov  4 19:46 .
> > > drwxr-xr-x 13 root root       0 Nov  4 19:46 ..
> > >
> > > ...
> > >
> > > -r--r--r--  1 root root     888 Nov  4 19:46 irqbypass
> > > -r--r--r--  1 root root  100225 Nov  4 19:46 kvm
> > > -r--r--r--  1 root root   35401 Nov  4 19:46 kvm_intel
> > > -r--r--r--  1 root root     120 Nov  4 19:46 pcspkr
> > > -r--r--r--  1 root root     399 Nov  4 19:46 serio_raw
> > > -r--r--r--  1 root root 4094095 Nov  4 19:46 vmlinux
> > >
> > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> > > ---
> > >  include/linux/bpf.h    |   2 +
> > >  include/linux/module.h |   4 +
> > >  kernel/bpf/btf.c       | 193 +++++++++++++++++++++++++++++++++++++++++
> > >  kernel/bpf/sysfs_btf.c |   2 +-
> > >  kernel/module.c        |  32 +++++++
> > >  5 files changed, 232 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 2fffd30e13ac..3cb89cd7177b 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -36,9 +36,11 @@ struct seq_operations;
> > >  struct bpf_iter_aux_info;
> > >  struct bpf_local_storage;
> > >  struct bpf_local_storage_map;
> > > +struct kobject;
> > >
> > >  extern struct idr btf_idr;
> > >  extern spinlock_t btf_idr_lock;
> > > +extern struct kobject *btf_kobj;
>
> I don't see any Documentation/ABI/ updates for the sysfs changes here,
> did I miss it?
>

Nope, my bad, completely forgot to add it. Last time I touched sysfs
was quite a while ago, I forgot about adding ABI description. Will add
in the next version.

> thanks,
>
> greg k-h

[RFC PATCH bpf-next 5/5] tools/bpftool: add support for in-kernel and named BTF in `btf show`

[Andrii Nakryiko]

Display vmlinux BTF name and kernel module names when listing available BTFs
on the system.

In human-readable output mode, module BTFs are reported with
"name [module-name]", while vmlinux BTF is reported as "name [vmlinux]".
vmlinux BTF, as returned from the kernel, has an empty name. Square brackets
are added by bpftool and follow kernel convention when displaying modules in
human-readable text outputs.

[vmuser@archvm bpf]$ sudo ../../../bpf/bpftool/bpftool btf s
1: name [vmlinux]  size 4082281B
6: size 2365B  prog_ids 8,6  map_ids 3
7: name [button]  size 46895B
8: name [pcspkr]  size 42328B
9: name [serio_raw]  size 39375B
10: name [floppy]  size 57185B
11: name [i2c_core]  size 76186B
12: name [crc32c_intel]  size 16036B
13: name [i2c_piix4]  size 50497B
14: name [irqbypass]  size 14124B
15: name [kvm]  size 197985B
16: name [kvm_intel]  size 123564B
17: name [cryptd]  size 42466B
18: name [crypto_simd]  size 17187B
19: name [glue_helper]  size 39205B
20: name [aesni_intel]  size 41034B
25: size 36150B
        pids bpftool(2519)

In JSON mode, two fields (boolean "kernel" and string "name") are reported for
each BTF object. vmlinux BTF is reported with name "vmlinux" (kernel itself
returns and empty name for vmlinux BTF).

[vmuser@archvm bpf]$ sudo ../../../bpf/bpftool/bpftool btf s -jp
[{
        "id": 1,
        "size": 4082281,
        "prog_ids": [],
        "map_ids": [],
        "kernel": true,
        "name": "vmlinux"
    },{
        "id": 6,
        "size": 2365,
        "prog_ids": [8,6
        ],
        "map_ids": [3
        ],
        "kernel": false
    },{
        "id": 7,
        "size": 46895,
        "prog_ids": [],
        "map_ids": [],
        "kernel": true,
        "name": "button"
    },{

...

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/bpf/bpftool/btf.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index c96b56e8e3a4..9a7ff9b4ba5f 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -742,9 +742,14 @@ show_btf_plain(struct bpf_btf_info *info, int fd,
 	       struct btf_attach_table *btf_map_table)
 {
 	struct btf_attach_point *obj;
+	const char *name = u64_to_ptr(info->name);
 	int n;
 
 	printf("%u: ", info->id);
+	if (info->kernel_btf)
+		printf("name [%s]  ", name && name[0] ? name : "vmlinux");
+	else if (name && name[0])
+		printf("name %s  ", name);
 	printf("size %uB", info->btf_size);
 
 	n = 0;
@@ -771,6 +776,7 @@ show_btf_json(struct bpf_btf_info *info, int fd,
 	      struct btf_attach_table *btf_map_table)
 {
 	struct btf_attach_point *obj;
+	const char *name = u64_to_ptr(info->name);
 
 	jsonw_start_object(json_wtr);	/* btf object */
 	jsonw_uint_field(json_wtr, "id", info->id);
@@ -796,6 +802,13 @@ show_btf_json(struct bpf_btf_info *info, int fd,
 
 	emit_obj_refs_json(&refs_table, info->id, json_wtr); /* pids */
 
+	jsonw_bool_field(json_wtr, "kernel", info->kernel_btf);
+
+	if (name && name[0])
+		jsonw_string_field(json_wtr, "name", name);
+	else if (info->kernel_btf)
+		jsonw_string_field(json_wtr, "name", "vmlinux");
+
 	jsonw_end_object(json_wtr);	/* btf object */
 }
 
@@ -803,15 +816,30 @@ static int
 show_btf(int fd, struct btf_attach_table *btf_prog_table,
 	 struct btf_attach_table *btf_map_table)
 {
-	struct bpf_btf_info info = {};
+	struct bpf_btf_info info;
 	__u32 len = sizeof(info);
+	char name[64];
 	int err;
 
+	memset(&info, 0, sizeof(info));
 	err = bpf_obj_get_info_by_fd(fd, &info, &len);
 	if (err) {
 		p_err("can't get BTF object info: %s", strerror(errno));
 		return -1;
 	}
+	/* if kernel support emitting BTF object name, pass name pointer */
+	if (info.name_len) {
+		memset(&info, 0, sizeof(info));
+		info.name_len = sizeof(name);
+		info.name = ptr_to_u64(name);
+		len = sizeof(info);
+
+		err = bpf_obj_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			p_err("can't get BTF object info: %s", strerror(errno));
+			return -1;
+		}
+	}
 
 	if (json_output)
 		show_btf_json(&info, fd, btf_prog_table, btf_map_table);
-- 
2.24.1