[PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Andrii Nakryiko]

For some types of BPF programs that utilize expected_attach_type, libbpf won't
set load_attr.expected_attach_type, even if expected_attach_type is known from
section definition. This was done to preserve backwards compatibility with old
kernels that didn't recognize expected_attach_type attribute yet (which was
added in 5e43f899b03a ("bpf: Check attach type at prog load time"). But this
is problematic for some BPF programs that utilize never features that require
kernel to know specific expected_attach_type (e.g., extended set of return
codes for cgroup_skb/egress programs).

This patch makes libbpf specify expected_attach_type by default, but also
detect support for this field in kernel and not set it during program load.
This allows to have a good metadata for bpf_program
(e.g., bpf_program__get_extected_attach_type()), but still work with old
kernels (for cases where it can work at all).

Additionally, due to expected_attach_type being always set for recognized
program types, bpf_program__attach_cgroup doesn't have to do extra checks to
determine correct attach type, so remove that additional logic.

Also adjust section_names selftest to account for this change.

More detailed discussion can be found in [0].

  [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/

Reported-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
v1->v2:
- fixed prog_type/expected_attach_type combo (Andrey);
- added comment explaining what we are doing in probe_exp_attach_type (Andrey).

 tools/lib/bpf/libbpf.c                        | 127 ++++++++++++------
 .../selftests/bpf/prog_tests/section_names.c  |  42 +++---
 2 files changed, 110 insertions(+), 59 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ff9174282a8c..c7393182e2ae 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -178,6 +178,8 @@ struct bpf_capabilities {
 	__u32 array_mmap:1;
 	/* BTF_FUNC_GLOBAL is supported */
 	__u32 btf_func_global:1;
+	/* kernel support for expected_attach_type in BPF_PROG_LOAD */
+	__u32 exp_attach_type:1;
 };
 
 enum reloc_type {
@@ -194,6 +196,22 @@ struct reloc_desc {
 	int sym_off;
 };
 
+struct bpf_sec_def;
+
+typedef struct bpf_link *(*attach_fn_t)(const struct bpf_sec_def *sec,
+					struct bpf_program *prog);
+
+struct bpf_sec_def {
+	const char *sec;
+	size_t len;
+	enum bpf_prog_type prog_type;
+	enum bpf_attach_type expected_attach_type;
+	bool is_exp_attach_type_optional;
+	bool is_attachable;
+	bool is_attach_btf;
+	attach_fn_t attach_fn;
+};
+
 /*
  * bpf_prog should be a better name but it has been used in
  * linux/filter.h.
@@ -204,6 +222,7 @@ struct bpf_program {
 	char *name;
 	int prog_ifindex;
 	char *section_name;
+	const struct bpf_sec_def *sec_def;
 	/* section_name with / replaced by _; makes recursive pinning
 	 * in bpf_object__pin_programs easier
 	 */
@@ -3315,6 +3334,37 @@ static int bpf_object__probe_array_mmap(struct bpf_object *obj)
 	return 0;
 }
 
+static int
+bpf_object__probe_exp_attach_type(struct bpf_object *obj)
+{
+	struct bpf_load_program_attr attr;
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	int fd;
+
+	memset(&attr, 0, sizeof(attr));
+	/* use any valid combination of program type and (optional)
+	 * non-zero expected attach type (i.e., not a BPF_CGROUP_INET_INGRESS)
+	 * to see if kernel supports expected_attach_type field for
+	 * BPF_PROG_LOAD command
+	 */
+	attr.prog_type = BPF_PROG_TYPE_CGROUP_SOCK;
+	attr.expected_attach_type = BPF_CGROUP_INET_SOCK_CREATE;
+	attr.insns = insns;
+	attr.insns_cnt = ARRAY_SIZE(insns);
+	attr.license = "GPL";
+
+	fd = bpf_load_program_xattr(&attr, NULL, 0);
+	if (fd >= 0) {
+		obj->caps.exp_attach_type = 1;
+		close(fd);
+		return 1;
+	}
+	return 0;
+}
+
 static int
 bpf_object__probe_caps(struct bpf_object *obj)
 {
@@ -3325,6 +3375,7 @@ bpf_object__probe_caps(struct bpf_object *obj)
 		bpf_object__probe_btf_func_global,
 		bpf_object__probe_btf_datasec,
 		bpf_object__probe_array_mmap,
+		bpf_object__probe_exp_attach_type,
 	};
 	int i, ret;
 
@@ -4861,7 +4912,12 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
 
 	memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
 	load_attr.prog_type = prog->type;
-	load_attr.expected_attach_type = prog->expected_attach_type;
+	/* old kernels might not support specifying expected_attach_type */
+	if (!prog->caps->exp_attach_type && prog->sec_def &&
+	    prog->sec_def->is_exp_attach_type_optional)
+		load_attr.expected_attach_type = 0;
+	else
+		load_attr.expected_attach_type = prog->expected_attach_type;
 	if (prog->caps->name)
 		load_attr.name = prog->name;
 	load_attr.insns = insns;
@@ -5062,6 +5118,8 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
 	return 0;
 }
 
+static const struct bpf_sec_def *find_sec_def(const char *sec_name);
+
 static struct bpf_object *
 __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 		   const struct bpf_object_open_opts *opts)
@@ -5117,24 +5175,17 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
 	bpf_object__elf_finish(obj);
 
 	bpf_object__for_each_program(prog, obj) {
-		enum bpf_prog_type prog_type;
-		enum bpf_attach_type attach_type;
-
-		if (prog->type != BPF_PROG_TYPE_UNSPEC)
-			continue;
-
-		err = libbpf_prog_type_by_name(prog->section_name, &prog_type,
-					       &attach_type);
-		if (err == -ESRCH)
+		prog->sec_def = find_sec_def(prog->section_name);
+		if (!prog->sec_def)
 			/* couldn't guess, but user might manually specify */
 			continue;
-		if (err)
-			goto out;
 
-		bpf_program__set_type(prog, prog_type);
-		bpf_program__set_expected_attach_type(prog, attach_type);
-		if (prog_type == BPF_PROG_TYPE_TRACING ||
-		    prog_type == BPF_PROG_TYPE_EXT)
+		bpf_program__set_type(prog, prog->sec_def->prog_type);
+		bpf_program__set_expected_attach_type(prog,
+				prog->sec_def->expected_attach_type);
+
+		if (prog->sec_def->prog_type == BPF_PROG_TYPE_TRACING ||
+		    prog->sec_def->prog_type == BPF_PROG_TYPE_EXT)
 			prog->attach_prog_fd = OPTS_GET(opts, attach_prog_fd, 0);
 	}
 
@@ -6223,23 +6274,33 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
 	prog->expected_attach_type = type;
 }
 
-#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
-	{ string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
+#define BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype_optional,	    \
+			  attachable, attach_btf)			    \
+	{								    \
+		.sec = string,						    \
+		.len = sizeof(string) - 1,				    \
+		.prog_type = ptype,					    \
+		.sec = string,						    \
+		.expected_attach_type = eatype,				    \
+		.is_exp_attach_type_optional = eatype_optional,		    \
+		.is_attachable = attachable,				    \
+		.is_attach_btf = attach_btf,				    \
+	}
 
 /* Programs that can NOT be attached. */
 #define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
 
 /* Programs that can be attached. */
 #define BPF_APROG_SEC(string, ptype, atype) \
-	BPF_PROG_SEC_IMPL(string, ptype, 0, 1, 0, atype)
+	BPF_PROG_SEC_IMPL(string, ptype, atype, true, 1, 0)
 
 /* Programs that must specify expected attach type at load time. */
 #define BPF_EAPROG_SEC(string, ptype, eatype) \
-	BPF_PROG_SEC_IMPL(string, ptype, eatype, 1, 0, eatype)
+	BPF_PROG_SEC_IMPL(string, ptype, eatype, false, 1, 0)
 
 /* Programs that use BTF to identify attach point */
 #define BPF_PROG_BTF(string, ptype, eatype) \
-	BPF_PROG_SEC_IMPL(string, ptype, eatype, 0, 1, 0)
+	BPF_PROG_SEC_IMPL(string, ptype, eatype, false, 0, 1)
 
 /* Programs that can be attached but attach type can't be identified by section
  * name. Kept for backward compatibility.
@@ -6253,11 +6314,6 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
 	__VA_ARGS__							    \
 }
 
-struct bpf_sec_def;
-
-typedef struct bpf_link *(*attach_fn_t)(const struct bpf_sec_def *sec,
-					struct bpf_program *prog);
-
 static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
 				      struct bpf_program *prog);
 static struct bpf_link *attach_tp(const struct bpf_sec_def *sec,
@@ -6269,17 +6325,6 @@ static struct bpf_link *attach_trace(const struct bpf_sec_def *sec,
 static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
 				   struct bpf_program *prog);
 
-struct bpf_sec_def {
-	const char *sec;
-	size_t len;
-	enum bpf_prog_type prog_type;
-	enum bpf_attach_type expected_attach_type;
-	bool is_attachable;
-	bool is_attach_btf;
-	enum bpf_attach_type attach_type;
-	attach_fn_t attach_fn;
-};
-
 static const struct bpf_sec_def section_defs[] = {
 	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
 	BPF_PROG_SEC("sk_reuseport",		BPF_PROG_TYPE_SK_REUSEPORT),
@@ -6713,7 +6758,7 @@ int libbpf_attach_type_by_name(const char *name,
 			continue;
 		if (!section_defs[i].is_attachable)
 			return -EINVAL;
-		*attach_type = section_defs[i].attach_type;
+		*attach_type = section_defs[i].expected_attach_type;
 		return 0;
 	}
 	pr_debug("failed to guess attach type based on ELF section name '%s'\n", name);
@@ -7542,7 +7587,6 @@ static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
 struct bpf_link *
 bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
 {
-	const struct bpf_sec_def *sec_def;
 	enum bpf_attach_type attach_type;
 	char errmsg[STRERR_BUFSIZE];
 	struct bpf_link *link;
@@ -7561,11 +7605,6 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
 	link->detach = &bpf_link__detach_fd;
 
 	attach_type = bpf_program__get_expected_attach_type(prog);
-	if (!attach_type) {
-		sec_def = find_sec_def(bpf_program__title(prog, false));
-		if (sec_def)
-			attach_type = sec_def->attach_type;
-	}
 	link_fd = bpf_link_create(prog_fd, cgroup_fd, attach_type, NULL);
 	if (link_fd < 0) {
 		link_fd = -errno;
diff --git a/tools/testing/selftests/bpf/prog_tests/section_names.c b/tools/testing/selftests/bpf/prog_tests/section_names.c
index 9d9351dc2ded..713167449c98 100644
--- a/tools/testing/selftests/bpf/prog_tests/section_names.c
+++ b/tools/testing/selftests/bpf/prog_tests/section_names.c
@@ -43,18 +43,18 @@ static struct sec_name_test tests[] = {
 	{"lwt_seg6local", {0, BPF_PROG_TYPE_LWT_SEG6LOCAL, 0}, {-EINVAL, 0} },
 	{
 		"cgroup_skb/ingress",
-		{0, BPF_PROG_TYPE_CGROUP_SKB, 0},
+		{0, BPF_PROG_TYPE_CGROUP_SKB, BPF_CGROUP_INET_INGRESS},
 		{0, BPF_CGROUP_INET_INGRESS},
 	},
 	{
 		"cgroup_skb/egress",
-		{0, BPF_PROG_TYPE_CGROUP_SKB, 0},
+		{0, BPF_PROG_TYPE_CGROUP_SKB, BPF_CGROUP_INET_EGRESS},
 		{0, BPF_CGROUP_INET_EGRESS},
 	},
 	{"cgroup/skb", {0, BPF_PROG_TYPE_CGROUP_SKB, 0}, {-EINVAL, 0} },
 	{
 		"cgroup/sock",
-		{0, BPF_PROG_TYPE_CGROUP_SOCK, 0},
+		{0, BPF_PROG_TYPE_CGROUP_SOCK, BPF_CGROUP_INET_SOCK_CREATE},
 		{0, BPF_CGROUP_INET_SOCK_CREATE},
 	},
 	{
@@ -69,26 +69,38 @@ static struct sec_name_test tests[] = {
 	},
 	{
 		"cgroup/dev",
-		{0, BPF_PROG_TYPE_CGROUP_DEVICE, 0},
+		{0, BPF_PROG_TYPE_CGROUP_DEVICE, BPF_CGROUP_DEVICE},
 		{0, BPF_CGROUP_DEVICE},
 	},
-	{"sockops", {0, BPF_PROG_TYPE_SOCK_OPS, 0}, {0, BPF_CGROUP_SOCK_OPS} },
+	{
+		"sockops",
+		{0, BPF_PROG_TYPE_SOCK_OPS, BPF_CGROUP_SOCK_OPS},
+		{0, BPF_CGROUP_SOCK_OPS},
+	},
 	{
 		"sk_skb/stream_parser",
-		{0, BPF_PROG_TYPE_SK_SKB, 0},
+		{0, BPF_PROG_TYPE_SK_SKB, BPF_SK_SKB_STREAM_PARSER},
 		{0, BPF_SK_SKB_STREAM_PARSER},
 	},
 	{
 		"sk_skb/stream_verdict",
-		{0, BPF_PROG_TYPE_SK_SKB, 0},
+		{0, BPF_PROG_TYPE_SK_SKB, BPF_SK_SKB_STREAM_VERDICT},
 		{0, BPF_SK_SKB_STREAM_VERDICT},
 	},
 	{"sk_skb", {0, BPF_PROG_TYPE_SK_SKB, 0}, {-EINVAL, 0} },
-	{"sk_msg", {0, BPF_PROG_TYPE_SK_MSG, 0}, {0, BPF_SK_MSG_VERDICT} },
-	{"lirc_mode2", {0, BPF_PROG_TYPE_LIRC_MODE2, 0}, {0, BPF_LIRC_MODE2} },
+	{
+		"sk_msg",
+		{0, BPF_PROG_TYPE_SK_MSG, BPF_SK_MSG_VERDICT},
+		{0, BPF_SK_MSG_VERDICT},
+	},
+	{
+		"lirc_mode2",
+		{0, BPF_PROG_TYPE_LIRC_MODE2, BPF_LIRC_MODE2},
+		{0, BPF_LIRC_MODE2},
+	},
 	{
 		"flow_dissector",
-		{0, BPF_PROG_TYPE_FLOW_DISSECTOR, 0},
+		{0, BPF_PROG_TYPE_FLOW_DISSECTOR, BPF_FLOW_DISSECTOR},
 		{0, BPF_FLOW_DISSECTOR},
 	},
 	{
@@ -158,17 +170,17 @@ static void test_prog_type_by_name(const struct sec_name_test *test)
 				      &expected_attach_type);
 
 	CHECK(rc != test->expected_load.rc, "check_code",
-	      "prog: unexpected rc=%d for %s", rc, test->sec_name);
+	      "prog: unexpected rc=%d for %s\n", rc, test->sec_name);
 
 	if (rc)
 		return;
 
 	CHECK(prog_type != test->expected_load.prog_type, "check_prog_type",
-	      "prog: unexpected prog_type=%d for %s",
+	      "prog: unexpected prog_type=%d for %s\n",
 	      prog_type, test->sec_name);
 
 	CHECK(expected_attach_type != test->expected_load.expected_attach_type,
-	      "check_attach_type", "prog: unexpected expected_attach_type=%d for %s",
+	      "check_attach_type", "prog: unexpected expected_attach_type=%d for %s\n",
 	      expected_attach_type, test->sec_name);
 }
 
@@ -180,13 +192,13 @@ static void test_attach_type_by_name(const struct sec_name_test *test)
 	rc = libbpf_attach_type_by_name(test->sec_name, &attach_type);
 
 	CHECK(rc != test->expected_attach.rc, "check_ret",
-	      "attach: unexpected rc=%d for %s", rc, test->sec_name);
+	      "attach: unexpected rc=%d for %s\n", rc, test->sec_name);
 
 	if (rc)
 		return;
 
 	CHECK(attach_type != test->expected_attach.attach_type,
-	      "check_attach_type", "attach: unexpected attach_type=%d for %s",
+	      "check_attach_type", "attach: unexpected attach_type=%d for %s\n",
 	      attach_type, test->sec_name);
 }
 
-- 
2.24.1

Re: [PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Song Liu]

> On Apr 13, 2020, at 9:56 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> For some types of BPF programs that utilize expected_attach_type, libbpf won't
> set load_attr.expected_attach_type, even if expected_attach_type is known from
> section definition. This was done to preserve backwards compatibility with old
> kernels that didn't recognize expected_attach_type attribute yet (which was
> added in 5e43f899b03a ("bpf: Check attach type at prog load time"). But this
> is problematic for some BPF programs that utilize never features that require
> kernel to know specific expected_attach_type (e.g., extended set of return
> codes for cgroup_skb/egress programs).
> 
> This patch makes libbpf specify expected_attach_type by default, but also
> detect support for this field in kernel and not set it during program load.
> This allows to have a good metadata for bpf_program
> (e.g., bpf_program__get_extected_attach_type()), but still work with old
> kernels (for cases where it can work at all).
> 
> Additionally, due to expected_attach_type being always set for recognized
> program types, bpf_program__attach_cgroup doesn't have to do extra checks to
> determine correct attach type, so remove that additional logic.
> 
> Also adjust section_names selftest to account for this change.
> 
> More detailed discussion can be found in [0].
> 
>  [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/
> 
> Reported-by: Andrey Ignatov <rdna@fb.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

With one nit below. 

> ---
> v1->v2:
> - fixed prog_type/expected_attach_type combo (Andrey);
> - added comment explaining what we are doing in probe_exp_attach_type (Andrey).
> 
> tools/lib/bpf/libbpf.c                        | 127 ++++++++++++------
> .../selftests/bpf/prog_tests/section_names.c  |  42 +++---
> 2 files changed, 110 insertions(+), 59 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ff9174282a8c..c7393182e2ae 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -178,6 +178,8 @@ struct bpf_capabilities {
> 	__u32 array_mmap:1;
> 	/* BTF_FUNC_GLOBAL is supported */
> 	__u32 btf_func_global:1;
> +	/* kernel support for expected_attach_type in BPF_PROG_LOAD */
> +	__u32 exp_attach_type:1;
> };

[...]

> -#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
> -	{ string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
> +#define BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype_optional,	    \
> +			  attachable, attach_btf)			    \
> +	{								    \
> +		.sec = string,						    \
> +		.len = sizeof(string) - 1,				    \
> +		.prog_type = ptype,					    \
> +		.sec = string,						    \

Two lines of ".sec = string". 

> +		.expected_attach_type = eatype,				    \
> +		.is_exp_attach_type_optional = eatype_optional,		    \
> +		.is_attachable = attachable,				    \
> +		.is_attach_btf = attach_btf,				    \
> +	}

Re: [PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Andrii Nakryiko]

On Tue, Apr 14, 2020 at 12:04 AM Song Liu <songliubraving@fb.com> wrote:
>
>
>
> > On Apr 13, 2020, at 9:56 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> >
> > For some types of BPF programs that utilize expected_attach_type, libbpf won't
> > set load_attr.expected_attach_type, even if expected_attach_type is known from
> > section definition. This was done to preserve backwards compatibility with old
> > kernels that didn't recognize expected_attach_type attribute yet (which was
> > added in 5e43f899b03a ("bpf: Check attach type at prog load time"). But this
> > is problematic for some BPF programs that utilize never features that require
> > kernel to know specific expected_attach_type (e.g., extended set of return
> > codes for cgroup_skb/egress programs).
> >
> > This patch makes libbpf specify expected_attach_type by default, but also
> > detect support for this field in kernel and not set it during program load.
> > This allows to have a good metadata for bpf_program
> > (e.g., bpf_program__get_extected_attach_type()), but still work with old
> > kernels (for cases where it can work at all).
> >
> > Additionally, due to expected_attach_type being always set for recognized
> > program types, bpf_program__attach_cgroup doesn't have to do extra checks to
> > determine correct attach type, so remove that additional logic.
> >
> > Also adjust section_names selftest to account for this change.
> >
> > More detailed discussion can be found in [0].
> >
> >  [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/
> >
> > Reported-by: Andrey Ignatov <rdna@fb.com>
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>
> Acked-by: Song Liu <songliubraving@fb.com>
>
> With one nit below.
>
> > ---
> > v1->v2:
> > - fixed prog_type/expected_attach_type combo (Andrey);
> > - added comment explaining what we are doing in probe_exp_attach_type (Andrey).
> >
> > tools/lib/bpf/libbpf.c                        | 127 ++++++++++++------
> > .../selftests/bpf/prog_tests/section_names.c  |  42 +++---
> > 2 files changed, 110 insertions(+), 59 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index ff9174282a8c..c7393182e2ae 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -178,6 +178,8 @@ struct bpf_capabilities {
> >       __u32 array_mmap:1;
> >       /* BTF_FUNC_GLOBAL is supported */
> >       __u32 btf_func_global:1;
> > +     /* kernel support for expected_attach_type in BPF_PROG_LOAD */
> > +     __u32 exp_attach_type:1;
> > };
>
> [...]
>
> > -#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
> > -     { string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
> > +#define BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype_optional,        \
> > +                       attachable, attach_btf)                           \
> > +     {                                                                   \
> > +             .sec = string,                                              \
> > +             .len = sizeof(string) - 1,                                  \
> > +             .prog_type = ptype,                                         \
> > +             .sec = string,                                              \
>
> Two lines of ".sec = string".


*facepalm*, will fix in next version, once bpf-next is open.

>
> > +             .expected_attach_type = eatype,                             \
> > +             .is_exp_attach_type_optional = eatype_optional,             \
> > +             .is_attachable = attachable,                                \
> > +             .is_attach_btf = attach_btf,                                \
> > +     }
>

Re: [PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Andrey Ignatov]

Andrii Nakryiko <andriin@fb.com> [Mon, 2020-04-13 21:56 -0700]:
> For some types of BPF programs that utilize expected_attach_type, libbpf won't
> set load_attr.expected_attach_type, even if expected_attach_type is known from
> section definition. This was done to preserve backwards compatibility with old
> kernels that didn't recognize expected_attach_type attribute yet (which was
> added in 5e43f899b03a ("bpf: Check attach type at prog load time"). But this
> is problematic for some BPF programs that utilize never features that require
> kernel to know specific expected_attach_type (e.g., extended set of return
> codes for cgroup_skb/egress programs).
> 
> This patch makes libbpf specify expected_attach_type by default, but also
> detect support for this field in kernel and not set it during program load.
> This allows to have a good metadata for bpf_program
> (e.g., bpf_program__get_extected_attach_type()), but still work with old
> kernels (for cases where it can work at all).
> 
> Additionally, due to expected_attach_type being always set for recognized
> program types, bpf_program__attach_cgroup doesn't have to do extra checks to
> determine correct attach type, so remove that additional logic.
> 
> Also adjust section_names selftest to account for this change.
> 
> More detailed discussion can be found in [0].
> 
>   [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/
> 
> Reported-by: Andrey Ignatov <rdna@fb.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---
> v1->v2:
> - fixed prog_type/expected_attach_type combo (Andrey);
> - added comment explaining what we are doing in probe_exp_attach_type (Andrey).

Thanks for changes.

I built the patch (removing the double .sec Song mentioned since it
breaks compilation) and tested it: it fixes the problem with NET_XMIT_CN
on old kernels and works for me with cgroup skb on old kernels.

Thank you!

Acked-by: Andrey Ignatov <rdna@fb.com>

I guess we can deal with selftest separately in the original thread.

Also a question about bpf vs bpf-next: since this fixes real problem
with loading cgroup skb programs, should it go to bpf tree instead?


>  tools/lib/bpf/libbpf.c                        | 127 ++++++++++++------
>  .../selftests/bpf/prog_tests/section_names.c  |  42 +++---
>  2 files changed, 110 insertions(+), 59 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index ff9174282a8c..c7393182e2ae 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -178,6 +178,8 @@ struct bpf_capabilities {
>  	__u32 array_mmap:1;
>  	/* BTF_FUNC_GLOBAL is supported */
>  	__u32 btf_func_global:1;
> +	/* kernel support for expected_attach_type in BPF_PROG_LOAD */
> +	__u32 exp_attach_type:1;
>  };
>  
>  enum reloc_type {
> @@ -194,6 +196,22 @@ struct reloc_desc {
>  	int sym_off;
>  };
>  
> +struct bpf_sec_def;
> +
> +typedef struct bpf_link *(*attach_fn_t)(const struct bpf_sec_def *sec,
> +					struct bpf_program *prog);
> +
> +struct bpf_sec_def {
> +	const char *sec;
> +	size_t len;
> +	enum bpf_prog_type prog_type;
> +	enum bpf_attach_type expected_attach_type;
> +	bool is_exp_attach_type_optional;
> +	bool is_attachable;
> +	bool is_attach_btf;
> +	attach_fn_t attach_fn;
> +};
> +
>  /*
>   * bpf_prog should be a better name but it has been used in
>   * linux/filter.h.
> @@ -204,6 +222,7 @@ struct bpf_program {
>  	char *name;
>  	int prog_ifindex;
>  	char *section_name;
> +	const struct bpf_sec_def *sec_def;
>  	/* section_name with / replaced by _; makes recursive pinning
>  	 * in bpf_object__pin_programs easier
>  	 */
> @@ -3315,6 +3334,37 @@ static int bpf_object__probe_array_mmap(struct bpf_object *obj)
>  	return 0;
>  }
>  
> +static int
> +bpf_object__probe_exp_attach_type(struct bpf_object *obj)
> +{
> +	struct bpf_load_program_attr attr;
> +	struct bpf_insn insns[] = {
> +		BPF_MOV64_IMM(BPF_REG_0, 0),
> +		BPF_EXIT_INSN(),
> +	};
> +	int fd;
> +
> +	memset(&attr, 0, sizeof(attr));
> +	/* use any valid combination of program type and (optional)
> +	 * non-zero expected attach type (i.e., not a BPF_CGROUP_INET_INGRESS)
> +	 * to see if kernel supports expected_attach_type field for
> +	 * BPF_PROG_LOAD command
> +	 */
> +	attr.prog_type = BPF_PROG_TYPE_CGROUP_SOCK;
> +	attr.expected_attach_type = BPF_CGROUP_INET_SOCK_CREATE;
> +	attr.insns = insns;
> +	attr.insns_cnt = ARRAY_SIZE(insns);
> +	attr.license = "GPL";
> +
> +	fd = bpf_load_program_xattr(&attr, NULL, 0);
> +	if (fd >= 0) {
> +		obj->caps.exp_attach_type = 1;
> +		close(fd);
> +		return 1;
> +	}
> +	return 0;
> +}
> +
>  static int
>  bpf_object__probe_caps(struct bpf_object *obj)
>  {
> @@ -3325,6 +3375,7 @@ bpf_object__probe_caps(struct bpf_object *obj)
>  		bpf_object__probe_btf_func_global,
>  		bpf_object__probe_btf_datasec,
>  		bpf_object__probe_array_mmap,
> +		bpf_object__probe_exp_attach_type,
>  	};
>  	int i, ret;
>  
> @@ -4861,7 +4912,12 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt,
>  
>  	memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
>  	load_attr.prog_type = prog->type;
> -	load_attr.expected_attach_type = prog->expected_attach_type;
> +	/* old kernels might not support specifying expected_attach_type */
> +	if (!prog->caps->exp_attach_type && prog->sec_def &&
> +	    prog->sec_def->is_exp_attach_type_optional)
> +		load_attr.expected_attach_type = 0;
> +	else
> +		load_attr.expected_attach_type = prog->expected_attach_type;
>  	if (prog->caps->name)
>  		load_attr.name = prog->name;
>  	load_attr.insns = insns;
> @@ -5062,6 +5118,8 @@ bpf_object__load_progs(struct bpf_object *obj, int log_level)
>  	return 0;
>  }
>  
> +static const struct bpf_sec_def *find_sec_def(const char *sec_name);
> +
>  static struct bpf_object *
>  __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
>  		   const struct bpf_object_open_opts *opts)
> @@ -5117,24 +5175,17 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
>  	bpf_object__elf_finish(obj);
>  
>  	bpf_object__for_each_program(prog, obj) {
> -		enum bpf_prog_type prog_type;
> -		enum bpf_attach_type attach_type;
> -
> -		if (prog->type != BPF_PROG_TYPE_UNSPEC)
> -			continue;
> -
> -		err = libbpf_prog_type_by_name(prog->section_name, &prog_type,
> -					       &attach_type);
> -		if (err == -ESRCH)
> +		prog->sec_def = find_sec_def(prog->section_name);
> +		if (!prog->sec_def)
>  			/* couldn't guess, but user might manually specify */
>  			continue;
> -		if (err)
> -			goto out;
>  
> -		bpf_program__set_type(prog, prog_type);
> -		bpf_program__set_expected_attach_type(prog, attach_type);
> -		if (prog_type == BPF_PROG_TYPE_TRACING ||
> -		    prog_type == BPF_PROG_TYPE_EXT)
> +		bpf_program__set_type(prog, prog->sec_def->prog_type);
> +		bpf_program__set_expected_attach_type(prog,
> +				prog->sec_def->expected_attach_type);
> +
> +		if (prog->sec_def->prog_type == BPF_PROG_TYPE_TRACING ||
> +		    prog->sec_def->prog_type == BPF_PROG_TYPE_EXT)
>  			prog->attach_prog_fd = OPTS_GET(opts, attach_prog_fd, 0);
>  	}
>  
> @@ -6223,23 +6274,33 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
>  	prog->expected_attach_type = type;
>  }
>  
> -#define BPF_PROG_SEC_IMPL(string, ptype, eatype, is_attachable, btf, atype) \
> -	{ string, sizeof(string) - 1, ptype, eatype, is_attachable, btf, atype }
> +#define BPF_PROG_SEC_IMPL(string, ptype, eatype, eatype_optional,	    \
> +			  attachable, attach_btf)			    \
> +	{								    \
> +		.sec = string,						    \
> +		.len = sizeof(string) - 1,				    \
> +		.prog_type = ptype,					    \
> +		.sec = string,						    \
> +		.expected_attach_type = eatype,				    \
> +		.is_exp_attach_type_optional = eatype_optional,		    \
> +		.is_attachable = attachable,				    \
> +		.is_attach_btf = attach_btf,				    \
> +	}
>  
>  /* Programs that can NOT be attached. */
>  #define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
>  
>  /* Programs that can be attached. */
>  #define BPF_APROG_SEC(string, ptype, atype) \
> -	BPF_PROG_SEC_IMPL(string, ptype, 0, 1, 0, atype)
> +	BPF_PROG_SEC_IMPL(string, ptype, atype, true, 1, 0)
>  
>  /* Programs that must specify expected attach type at load time. */
>  #define BPF_EAPROG_SEC(string, ptype, eatype) \
> -	BPF_PROG_SEC_IMPL(string, ptype, eatype, 1, 0, eatype)
> +	BPF_PROG_SEC_IMPL(string, ptype, eatype, false, 1, 0)
>  
>  /* Programs that use BTF to identify attach point */
>  #define BPF_PROG_BTF(string, ptype, eatype) \
> -	BPF_PROG_SEC_IMPL(string, ptype, eatype, 0, 1, 0)
> +	BPF_PROG_SEC_IMPL(string, ptype, eatype, false, 0, 1)
>  
>  /* Programs that can be attached but attach type can't be identified by section
>   * name. Kept for backward compatibility.
> @@ -6253,11 +6314,6 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
>  	__VA_ARGS__							    \
>  }
>  
> -struct bpf_sec_def;
> -
> -typedef struct bpf_link *(*attach_fn_t)(const struct bpf_sec_def *sec,
> -					struct bpf_program *prog);
> -
>  static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
>  				      struct bpf_program *prog);
>  static struct bpf_link *attach_tp(const struct bpf_sec_def *sec,
> @@ -6269,17 +6325,6 @@ static struct bpf_link *attach_trace(const struct bpf_sec_def *sec,
>  static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
>  				   struct bpf_program *prog);
>  
> -struct bpf_sec_def {
> -	const char *sec;
> -	size_t len;
> -	enum bpf_prog_type prog_type;
> -	enum bpf_attach_type expected_attach_type;
> -	bool is_attachable;
> -	bool is_attach_btf;
> -	enum bpf_attach_type attach_type;
> -	attach_fn_t attach_fn;
> -};
> -
>  static const struct bpf_sec_def section_defs[] = {
>  	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
>  	BPF_PROG_SEC("sk_reuseport",		BPF_PROG_TYPE_SK_REUSEPORT),
> @@ -6713,7 +6758,7 @@ int libbpf_attach_type_by_name(const char *name,
>  			continue;
>  		if (!section_defs[i].is_attachable)
>  			return -EINVAL;
> -		*attach_type = section_defs[i].attach_type;
> +		*attach_type = section_defs[i].expected_attach_type;
>  		return 0;
>  	}
>  	pr_debug("failed to guess attach type based on ELF section name '%s'\n", name);
> @@ -7542,7 +7587,6 @@ static struct bpf_link *attach_lsm(const struct bpf_sec_def *sec,
>  struct bpf_link *
>  bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>  {
> -	const struct bpf_sec_def *sec_def;
>  	enum bpf_attach_type attach_type;
>  	char errmsg[STRERR_BUFSIZE];
>  	struct bpf_link *link;
> @@ -7561,11 +7605,6 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>  	link->detach = &bpf_link__detach_fd;
>  
>  	attach_type = bpf_program__get_expected_attach_type(prog);
> -	if (!attach_type) {
> -		sec_def = find_sec_def(bpf_program__title(prog, false));
> -		if (sec_def)
> -			attach_type = sec_def->attach_type;
> -	}
>  	link_fd = bpf_link_create(prog_fd, cgroup_fd, attach_type, NULL);
>  	if (link_fd < 0) {
>  		link_fd = -errno;
> diff --git a/tools/testing/selftests/bpf/prog_tests/section_names.c b/tools/testing/selftests/bpf/prog_tests/section_names.c
> index 9d9351dc2ded..713167449c98 100644
> --- a/tools/testing/selftests/bpf/prog_tests/section_names.c
> +++ b/tools/testing/selftests/bpf/prog_tests/section_names.c
> @@ -43,18 +43,18 @@ static struct sec_name_test tests[] = {
>  	{"lwt_seg6local", {0, BPF_PROG_TYPE_LWT_SEG6LOCAL, 0}, {-EINVAL, 0} },
>  	{
>  		"cgroup_skb/ingress",
> -		{0, BPF_PROG_TYPE_CGROUP_SKB, 0},
> +		{0, BPF_PROG_TYPE_CGROUP_SKB, BPF_CGROUP_INET_INGRESS},
>  		{0, BPF_CGROUP_INET_INGRESS},
>  	},
>  	{
>  		"cgroup_skb/egress",
> -		{0, BPF_PROG_TYPE_CGROUP_SKB, 0},
> +		{0, BPF_PROG_TYPE_CGROUP_SKB, BPF_CGROUP_INET_EGRESS},
>  		{0, BPF_CGROUP_INET_EGRESS},
>  	},
>  	{"cgroup/skb", {0, BPF_PROG_TYPE_CGROUP_SKB, 0}, {-EINVAL, 0} },
>  	{
>  		"cgroup/sock",
> -		{0, BPF_PROG_TYPE_CGROUP_SOCK, 0},
> +		{0, BPF_PROG_TYPE_CGROUP_SOCK, BPF_CGROUP_INET_SOCK_CREATE},
>  		{0, BPF_CGROUP_INET_SOCK_CREATE},
>  	},
>  	{
> @@ -69,26 +69,38 @@ static struct sec_name_test tests[] = {
>  	},
>  	{
>  		"cgroup/dev",
> -		{0, BPF_PROG_TYPE_CGROUP_DEVICE, 0},
> +		{0, BPF_PROG_TYPE_CGROUP_DEVICE, BPF_CGROUP_DEVICE},
>  		{0, BPF_CGROUP_DEVICE},
>  	},
> -	{"sockops", {0, BPF_PROG_TYPE_SOCK_OPS, 0}, {0, BPF_CGROUP_SOCK_OPS} },
> +	{
> +		"sockops",
> +		{0, BPF_PROG_TYPE_SOCK_OPS, BPF_CGROUP_SOCK_OPS},
> +		{0, BPF_CGROUP_SOCK_OPS},
> +	},
>  	{
>  		"sk_skb/stream_parser",
> -		{0, BPF_PROG_TYPE_SK_SKB, 0},
> +		{0, BPF_PROG_TYPE_SK_SKB, BPF_SK_SKB_STREAM_PARSER},
>  		{0, BPF_SK_SKB_STREAM_PARSER},
>  	},
>  	{
>  		"sk_skb/stream_verdict",
> -		{0, BPF_PROG_TYPE_SK_SKB, 0},
> +		{0, BPF_PROG_TYPE_SK_SKB, BPF_SK_SKB_STREAM_VERDICT},
>  		{0, BPF_SK_SKB_STREAM_VERDICT},
>  	},
>  	{"sk_skb", {0, BPF_PROG_TYPE_SK_SKB, 0}, {-EINVAL, 0} },
> -	{"sk_msg", {0, BPF_PROG_TYPE_SK_MSG, 0}, {0, BPF_SK_MSG_VERDICT} },
> -	{"lirc_mode2", {0, BPF_PROG_TYPE_LIRC_MODE2, 0}, {0, BPF_LIRC_MODE2} },
> +	{
> +		"sk_msg",
> +		{0, BPF_PROG_TYPE_SK_MSG, BPF_SK_MSG_VERDICT},
> +		{0, BPF_SK_MSG_VERDICT},
> +	},
> +	{
> +		"lirc_mode2",
> +		{0, BPF_PROG_TYPE_LIRC_MODE2, BPF_LIRC_MODE2},
> +		{0, BPF_LIRC_MODE2},
> +	},
>  	{
>  		"flow_dissector",
> -		{0, BPF_PROG_TYPE_FLOW_DISSECTOR, 0},
> +		{0, BPF_PROG_TYPE_FLOW_DISSECTOR, BPF_FLOW_DISSECTOR},
>  		{0, BPF_FLOW_DISSECTOR},
>  	},
>  	{
> @@ -158,17 +170,17 @@ static void test_prog_type_by_name(const struct sec_name_test *test)
>  				      &expected_attach_type);
>  
>  	CHECK(rc != test->expected_load.rc, "check_code",
> -	      "prog: unexpected rc=%d for %s", rc, test->sec_name);
> +	      "prog: unexpected rc=%d for %s\n", rc, test->sec_name);
>  
>  	if (rc)
>  		return;
>  
>  	CHECK(prog_type != test->expected_load.prog_type, "check_prog_type",
> -	      "prog: unexpected prog_type=%d for %s",
> +	      "prog: unexpected prog_type=%d for %s\n",
>  	      prog_type, test->sec_name);
>  
>  	CHECK(expected_attach_type != test->expected_load.expected_attach_type,
> -	      "check_attach_type", "prog: unexpected expected_attach_type=%d for %s",
> +	      "check_attach_type", "prog: unexpected expected_attach_type=%d for %s\n",
>  	      expected_attach_type, test->sec_name);
>  }
>  
> @@ -180,13 +192,13 @@ static void test_attach_type_by_name(const struct sec_name_test *test)
>  	rc = libbpf_attach_type_by_name(test->sec_name, &attach_type);
>  
>  	CHECK(rc != test->expected_attach.rc, "check_ret",
> -	      "attach: unexpected rc=%d for %s", rc, test->sec_name);
> +	      "attach: unexpected rc=%d for %s\n", rc, test->sec_name);
>  
>  	if (rc)
>  		return;
>  
>  	CHECK(attach_type != test->expected_attach.attach_type,
> -	      "check_attach_type", "attach: unexpected attach_type=%d for %s",
> +	      "check_attach_type", "attach: unexpected attach_type=%d for %s\n",
>  	      attach_type, test->sec_name);
>  }
>  
> -- 
> 2.24.1
> 

-- 
Andrey Ignatov

Re: [PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Andrii Nakryiko]

On Tue, Apr 14, 2020 at 10:56 AM Andrey Ignatov <rdna@fb.com> wrote:
>
> Andrii Nakryiko <andriin@fb.com> [Mon, 2020-04-13 21:56 -0700]:
> > For some types of BPF programs that utilize expected_attach_type, libbpf won't
> > set load_attr.expected_attach_type, even if expected_attach_type is known from
> > section definition. This was done to preserve backwards compatibility with old
> > kernels that didn't recognize expected_attach_type attribute yet (which was
> > added in 5e43f899b03a ("bpf: Check attach type at prog load time"). But this
> > is problematic for some BPF programs that utilize never features that require
> > kernel to know specific expected_attach_type (e.g., extended set of return
> > codes for cgroup_skb/egress programs).
> >
> > This patch makes libbpf specify expected_attach_type by default, but also
> > detect support for this field in kernel and not set it during program load.
> > This allows to have a good metadata for bpf_program
> > (e.g., bpf_program__get_extected_attach_type()), but still work with old
> > kernels (for cases where it can work at all).
> >
> > Additionally, due to expected_attach_type being always set for recognized
> > program types, bpf_program__attach_cgroup doesn't have to do extra checks to
> > determine correct attach type, so remove that additional logic.
> >
> > Also adjust section_names selftest to account for this change.
> >
> > More detailed discussion can be found in [0].
> >
> >   [0] https://lore.kernel.org/bpf/20200412003604.GA15986@rdna-mbp.dhcp.thefacebook.com/
> >
> > Reported-by: Andrey Ignatov <rdna@fb.com>
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> > ---
> > v1->v2:
> > - fixed prog_type/expected_attach_type combo (Andrey);
> > - added comment explaining what we are doing in probe_exp_attach_type (Andrey).
>
> Thanks for changes.
>
> I built the patch (removing the double .sec Song mentioned since it
> breaks compilation) and tested it: it fixes the problem with NET_XMIT_CN

Wait, what? How does it break compilation? I compiled and tested
before submitting and just cleaned and built again, no compilation
errors or even warnings. Can you share compilation error you got,
please?

> on old kernels and works for me with cgroup skb on old kernels.
>
> Thank you!
>
> Acked-by: Andrey Ignatov <rdna@fb.com>

Thanks!

>
> I guess we can deal with selftest separately in the original thread.

Sure, if this is going to be applied to bpf as a fix, I'd rather
follow-up with selftests separately.

>
> Also a question about bpf vs bpf-next: since this fixes real problem
> with loading cgroup skb programs, should it go to bpf tree instead?

It will be up to maintainers, it's not so clear whether it's a new
feature or a bug fix.. I don't mind either way.

>
>
> >  tools/lib/bpf/libbpf.c                        | 127 ++++++++++++------
> >  .../selftests/bpf/prog_tests/section_names.c  |  42 +++---
> >  2 files changed, 110 insertions(+), 59 deletions(-)
> >

[...]

trimming :)

Re: [PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Andrey Ignatov]

Andrii Nakryiko <andrii.nakryiko@gmail.com> [Tue, 2020-04-14 11:25 -0700]:
> On Tue, Apr 14, 2020 at 10:56 AM Andrey Ignatov <rdna@fb.com> wrote:
> >
> > Andrii Nakryiko <andriin@fb.com> [Mon, 2020-04-13 21:56 -0700]:

...

> > > v1->v2:
> > > - fixed prog_type/expected_attach_type combo (Andrey);
> > > - added comment explaining what we are doing in probe_exp_attach_type (Andrey).
> >
> > Thanks for changes.
> >
> > I built the patch (removing the double .sec Song mentioned since it
> > breaks compilation) and tested it: it fixes the problem with NET_XMIT_CN
> 
> Wait, what? How does it break compilation? I compiled and tested
> before submitting and just cleaned and built again, no compilation
> errors or even warnings. Can you share compilation error you got,
> please?

Sure:

	11:37:28 1 rdna@dev082.prn2:~/bpf-next$>/home/rdna/bin/clang --version
	clang version 9.0.20190721
	Target: x86_64-unknown-linux-gnu
	Thread model: posix
	InstalledDir: /home/rdna/bin
	11:37:32 0 rdna@dev082.prn2:~/bpf-next$>env GCC=~/bin/gcc CLANG=~/bin/clang CC=~/bin/clang LLC=~/bin/llc LLVM_STRIP=~/bin/llvm-strip  make V=1 -C tools/bpf/bpftool/
	
	Auto-detecting system features:
	...                        libbfd: [ on  ]
	...        disassembler-four-args: [ OFF ]
	...                          zlib: [ on  ]
	...          clang-bpf-global-var: [ on  ]
	
	make: Entering directory `/home/rdna/bpf-next/tools/bpf/bpftool'
	make -C /home/rdna/bpf-next/tools/lib/bpf/ OUTPUT= libbpf.a
	make[1]: Entering directory `/home/rdna/bpf-next/tools/lib/bpf'
	make -f /home/rdna/bpf-next/tools/build/Makefile.build dir=. obj=libbpf OUTPUT=staticobjs/
	  /home/rdna/bin/clang -Wp,-MD,staticobjs/.libbpf.o.d -Wp,-MT,staticobjs/libbpf.o -g -Wall -DHAVE_LIBELF_MMAP_SUPPORT -DCOMPAT_NEED_REALLOCARRAY -Wbad-function-cast -Wdeclaration-after-statement -Wformat-security -Wformat-y2k -Winit-self -Wmissing-declarations -Wmissing-prototypes -Wnested-externs -Wno-system-headers -Wold-style-definition -Wpacked -Wredundant-decls -Wstrict-prototypes -Wswitch-default -Wswitch-enum -Wundef -Wwrite-strings -Wformat -fno-strict-aliasing -Wno-shadow -Werror -Wall -fPIC -I. -I/home/rdna/bpf-next/tools/include -I/home/rdna/bpf-next/tools/arch/x86/include/uapi -I/home/rdna/bpf-next/tools/include/uapi -fvisibility=hidden -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -D"BUILD_STR(s)=#s" -c -o staticobjs/libbpf.o libbpf.c
	libbpf.c:6329:15: error: initializer overrides prior initialization of this subobject [-Werror,-Winitializer-overrides]
	        BPF_PROG_SEC("socket",                  BPF_PROG_TYPE_SOCKET_FILTER),
	                     ^~~~~~~~
	libbpf.c:6291:55: note: expanded from macro 'BPF_PROG_SEC'
	#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
	                                                      ^~~~~~
	libbpf.c:6283:10: note: expanded from macro 'BPF_PROG_SEC_IMPL'
	                .sec = string,                                              \
	                       ^~~~~~
	libbpf.c:6329:15: note: previous initialization is here
	        BPF_PROG_SEC("socket",                  BPF_PROG_TYPE_SOCKET_FILTER),
	                     ^~~~~~~~
	libbpf.c:6291:55: note: expanded from macro 'BPF_PROG_SEC'
	#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
	                                                      ^~~~~~
	libbpf.c:6280:10: note: expanded from macro 'BPF_PROG_SEC_IMPL'
	                .sec = string,                                              \
	                       ^~~~~~
	libbpf.c:6330:15: error: initializer overrides prior initialization of this subobject [-Werror,-Winitializer-overrides]
	        BPF_PROG_SEC("sk_reuseport",            BPF_PROG_TYPE_SK_REUSEPORT),
	                     ^~~~~~~~~~~~~~
	libbpf.c:6291:55: note: expanded from macro 'BPF_PROG_SEC'
	#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
	                                                      ^~~~~~
	libbpf.c:6283:10: note: expanded from macro 'BPF_PROG_SEC_IMPL'
	                .sec = string,                                              \
	                       ^~~~~~
	libbpf.c:6330:15: note: previous initialization is here
	        BPF_PROG_SEC("sk_reuseport",            BPF_PROG_TYPE_SK_REUSEPORT),
	                     ^~~~~~~~~~~~~~
	libbpf.c:6291:55: note: expanded from macro 'BPF_PROG_SEC'
	#define BPF_PROG_SEC(string, ptype) BPF_PROG_SEC_IMPL(string, ptype, 0, 0, 0, 0)
	                                                      ^~~~~~
	libbpf.c:6280:10: note: expanded from macro 'BPF_PROG_SEC_IMPL'
	                .sec = string,                                              \
	                       ^~~~~~
	
	... and so on ...
	
	fatal error: too many errors emitted, stopping now [-ferror-limit=]
	20 errors generated.
	   ld -r -o staticobjs/libbpf-in.o  staticobjs/libbpf.o staticobjs/bpf.o staticobjs/nlattr.o staticobjs/btf.o staticobjs/libbpf_errno.o staticobjs/str_error.o staticobjs/netlink.o staticobjs/bpf_prog_linfo.o staticobjs/libbpf_probes.o staticobjs/xsk.o staticobjs/hashmap.o staticobjs/btf_dump.o
	ld: cannot find staticobjs/libbpf.o: No such file or directory
	make[2]: *** [staticobjs/libbpf-in.o] Error 1
	make[1]: *** [staticobjs/libbpf-in.o] Error 2
	make[1]: Leaving directory `/home/rdna/bpf-next/tools/lib/bpf'
	make: *** [/home/rdna/bpf-next/tools/lib/bpf/libbpf.a] Error 2
	make: Leaving directory `/home/rdna/bpf-next/tools/bpf/bpftool'
	11:37:43 2 rdna@dev082.prn2:~/bpf-next$>

> > I guess we can deal with selftest separately in the original thread.
> 
> Sure, if this is going to be applied to bpf as a fix, I'd rather
> follow-up with selftests separately.

Sounds good.

> > Also a question about bpf vs bpf-next: since this fixes real problem
> > with loading cgroup skb programs, should it go to bpf tree instead?
> 
> It will be up to maintainers, it's not so clear whether it's a new
> feature or a bug fix.. I don't mind either way.

Sounds good. Thanks.

-- 
Andrey Ignatov

Re: [PATCH v2 bpf-next] libbpf: always specify expected_attach_type on program load if supported

[Andrii Nakryiko]

On Tue, Apr 14, 2020 at 11:44 AM Andrey Ignatov <rdna@fb.com> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@gmail.com> [Tue, 2020-04-14 11:25 -0700]:
> > On Tue, Apr 14, 2020 at 10:56 AM Andrey Ignatov <rdna@fb.com> wrote:
> > >
> > > Andrii Nakryiko <andriin@fb.com> [Mon, 2020-04-13 21:56 -0700]:
>
> ...
>
> > > > v1->v2:
> > > > - fixed prog_type/expected_attach_type combo (Andrey);
> > > > - added comment explaining what we are doing in probe_exp_attach_type (Andrey).
> > >
> > > Thanks for changes.
> > >
> > > I built the patch (removing the double .sec Song mentioned since it
> > > breaks compilation) and tested it: it fixes the problem with NET_XMIT_CN
> >
> > Wait, what? How does it break compilation? I compiled and tested
> > before submitting and just cleaned and built again, no compilation
> > errors or even warnings. Can you share compilation error you got,
> > please?
>
> Sure:
>
>         11:37:28 1 rdna@dev082.prn2:~/bpf-next$>/home/rdna/bin/clang --version
>         clang version 9.0.20190721
>         Target: x86_64-unknown-linux-gnu
>         Thread model: posix
>         InstalledDir: /home/rdna/bin
>         11:37:32 0 rdna@dev082.prn2:~/bpf-next$>env GCC=~/bin/gcc CLANG=~/bin/clang CC=~/bin/clang LLC=~/bin/llc LLVM_STRIP=~/bin/llvm-strip  make V=1 -C tools/bpf/bpftool/

[...]

>
>         fatal error: too many errors emitted, stopping now [-ferror-limit=]
>         20 errors generated.
>            ld -r -o staticobjs/libbpf-in.o  staticobjs/libbpf.o staticobjs/bpf.o staticobjs/nlattr.o staticobjs/btf.o staticobjs/libbpf_errno.o staticobjs/str_error.o staticobjs/netlink.o staticobjs/bpf_prog_linfo.o staticobjs/libbpf_probes.o staticobjs/xsk.o staticobjs/hashmap.o staticobjs/btf_dump.o
>         ld: cannot find staticobjs/libbpf.o: No such file or directory
>         make[2]: *** [staticobjs/libbpf-in.o] Error 1
>         make[1]: *** [staticobjs/libbpf-in.o] Error 2
>         make[1]: Leaving directory `/home/rdna/bpf-next/tools/lib/bpf'
>         make: *** [/home/rdna/bpf-next/tools/lib/bpf/libbpf.a] Error 2
>         make: Leaving directory `/home/rdna/bpf-next/tools/bpf/bpftool'
>         11:37:43 2 rdna@dev082.prn2:~/bpf-next$>

Weird, I can't repro it locally neither with GCC, nor with clang-9 or
latest clang...

>
> > > I guess we can deal with selftest separately in the original thread.
> >
> > Sure, if this is going to be applied to bpf as a fix, I'd rather
> > follow-up with selftests separately.
>
> Sounds good.
>
> > > Also a question about bpf vs bpf-next: since this fixes real problem
> > > with loading cgroup skb programs, should it go to bpf tree instead?
> >
> > It will be up to maintainers, it's not so clear whether it's a new
> > feature or a bug fix.. I don't mind either way.
>
> Sounds good. Thanks.
>
> --
> Andrey Ignatov