libbpf: Refactor ELF section handler definitions

Refactor ELF section handler definitions table to use a set of flags and
unified SEC_DEF() macro. This allows for more succinct and table-like
set of definitions, and allows to more easily extend the logic without
adding more verbosity (this is utilized in later patches in the series).

This approach is also making libbpf-internal program pre-load callback
not rely on bpf_sec_def definition, which demonstrates that future
pluggable ELF section handlers will be able to achieve similar level of
integration without libbpf having to expose extra types and APIs.

For starters, update SEC_DEF() definitions and make them more succinct.
Also convert BPF_PROG_SEC() and BPF_APROG_COMPAT() definitions to
a common SEC_DEF() use.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20210928161946.2512801-8-andrii@kernel.org

tools/lib/bpf/libbpf.c

@@ -224,19 +224,35 @@ typedef int (*init_fn_t)(struct bpf_program *prog, long cookie);
 typedef int (*preload_fn_t)(struct bpf_program *prog, struct bpf_prog_load_params *attr, long cookie);
 typedef struct bpf_link *(*attach_fn_t)(const struct bpf_program *prog, long cookie);
 
+/* stored as sec_def->cookie for all libbpf-supported SEC()s */
+enum sec_def_flags {
+	SEC_NONE = 0,
+	/* expected_attach_type is optional, if kernel doesn't support that */
+	SEC_EXP_ATTACH_OPT = 1,
+	/* legacy, only used by libbpf_get_type_names() and
+	 * libbpf_attach_type_by_name(), not used by libbpf itself at all.
+	 * This used to be associated with cgroup (and few other) BPF programs
+	 * that were attachable through BPF_PROG_ATTACH command. Pretty
+	 * meaningless nowadays, though.
+	 */
+	SEC_ATTACHABLE = 2,
+	SEC_ATTACHABLE_OPT = SEC_ATTACHABLE | SEC_EXP_ATTACH_OPT,
+	/* attachment target is specified through BTF ID in either kernel or
+	 * other BPF program's BTF object */
+	SEC_ATTACH_BTF = 4,
+	/* BPF program type allows sleeping/blocking in kernel */
+	SEC_SLEEPABLE = 8,
+};
+
 struct bpf_sec_def {
 	const char *sec;
 	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;
-	bool is_sleepable;
+	long cookie;
 
 	init_fn_t init_fn;
 	preload_fn_t preload_fn;
 	attach_fn_t attach_fn;
-	long cookie;
 };
 
 /*
@@ -6100,26 +6116,30 @@ static int bpf_object__sanitize_prog(struct bpf_object *obj, struct bpf_program
 	return 0;
 }
 
-static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd, int *btf_type_id);
+static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attach_name,
+				     int *btf_obj_fd, int *btf_type_id);
 
 /* this is called as prog->sec_def->preload_fn for libbpf-supported sec_defs */
 static int libbpf_preload_prog(struct bpf_program *prog,
 			       struct bpf_prog_load_params *attr, long cookie)
 {
+	enum sec_def_flags def = cookie;
+
 	/* old kernels might not support specifying expected_attach_type */
-	if (prog->sec_def->is_exp_attach_type_optional &&
-	    !kernel_supports(prog->obj, FEAT_EXP_ATTACH_TYPE))
+	if ((def & SEC_EXP_ATTACH_OPT) && !kernel_supports(prog->obj, FEAT_EXP_ATTACH_TYPE))
 		attr->expected_attach_type = 0;
 
-	if (prog->sec_def->is_sleepable)
+	if (def & SEC_SLEEPABLE)
 		attr->prog_flags |= BPF_F_SLEEPABLE;
 
 	if ((prog->type == BPF_PROG_TYPE_TRACING ||
 	     prog->type == BPF_PROG_TYPE_LSM ||
 	     prog->type == BPF_PROG_TYPE_EXT) && !prog->attach_btf_id) {
 		int btf_obj_fd = 0, btf_type_id = 0, err;
+		const char *attach_name;
 
-		err = libbpf_find_attach_btf_id(prog, &btf_obj_fd, &btf_type_id);
+		attach_name = strchr(prog->sec_name, '/') + 1;
+		err = libbpf_find_attach_btf_id(prog, attach_name, &btf_obj_fd, &btf_type_id);
 		if (err)
 			return err;
 
@@ -7956,15 +7976,14 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
 		.sec = string,						    \
 		.prog_type = ptype,					    \
 		.expected_attach_type = eatype,				    \
-		.is_exp_attach_type_optional = eatype_optional,		    \
-		.is_attachable = attachable,				    \
-		.is_attach_btf = attach_btf,				    \
+		.cookie = (long) (					    \
+			(eatype_optional ? SEC_EXP_ATTACH_OPT : 0) |   \
+			(attachable ? SEC_ATTACHABLE : 0) |		    \
+			(attach_btf ? SEC_ATTACH_BTF : 0)		    \
+		),							    \
 		.preload_fn = libbpf_preload_prog,			    \
 	}
 
-/* 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, atype, true, 1, 0)
@@ -7977,14 +7996,11 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog,
 #define BPF_PROG_BTF(string, ptype, eatype) \
 	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.
- */
-#define BPF_APROG_COMPAT(string, ptype) BPF_PROG_SEC(string, ptype)
-
-#define SEC_DEF(sec_pfx, ptype, ...) {					    \
+#define SEC_DEF(sec_pfx, ptype, atype, flags, ...) {			    \
 	.sec = sec_pfx,							    \
 	.prog_type = BPF_PROG_TYPE_##ptype,				    \
+	.expected_attach_type = atype,					    \
+	.cookie = (long)(flags),					    \
 	.preload_fn = libbpf_preload_prog,				    \
 	__VA_ARGS__							    \
 }
@@ -7997,93 +8013,50 @@ static struct bpf_link *attach_lsm(const struct bpf_program *prog, long cookie);
 static struct bpf_link *attach_iter(const struct bpf_program *prog, long cookie);
 
 static const struct bpf_sec_def section_defs[] = {
-	BPF_PROG_SEC("socket",			BPF_PROG_TYPE_SOCKET_FILTER),
+	SEC_DEF("socket",		SOCKET_FILTER, 0, SEC_NONE),
 	BPF_EAPROG_SEC("sk_reuseport/migrate",	BPF_PROG_TYPE_SK_REUSEPORT,
 						BPF_SK_REUSEPORT_SELECT_OR_MIGRATE),
 	BPF_EAPROG_SEC("sk_reuseport",		BPF_PROG_TYPE_SK_REUSEPORT,
 						BPF_SK_REUSEPORT_SELECT),
-	SEC_DEF("kprobe/", KPROBE,
-		.attach_fn = attach_kprobe),
-	BPF_PROG_SEC("uprobe/",			BPF_PROG_TYPE_KPROBE),
-	SEC_DEF("kretprobe/", KPROBE,
-		.attach_fn = attach_kprobe),
-	BPF_PROG_SEC("uretprobe/",		BPF_PROG_TYPE_KPROBE),
-	BPF_PROG_SEC("classifier",		BPF_PROG_TYPE_SCHED_CLS),
-	BPF_PROG_SEC("tc",			BPF_PROG_TYPE_SCHED_CLS),
-	BPF_PROG_SEC("action",			BPF_PROG_TYPE_SCHED_ACT),
-	SEC_DEF("tracepoint/", TRACEPOINT,
-		.attach_fn = attach_tp),
-	SEC_DEF("tp/", TRACEPOINT,
-		.attach_fn = attach_tp),
-	SEC_DEF("raw_tracepoint/", RAW_TRACEPOINT,
-		.attach_fn = attach_raw_tp),
-	SEC_DEF("raw_tp/", RAW_TRACEPOINT,
-		.attach_fn = attach_raw_tp),
-	SEC_DEF("tp_btf/", TRACING,
-		.expected_attach_type = BPF_TRACE_RAW_TP,
-		.is_attach_btf = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("fentry/", TRACING,
-		.expected_attach_type = BPF_TRACE_FENTRY,
-		.is_attach_btf = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("fmod_ret/", TRACING,
-		.expected_attach_type = BPF_MODIFY_RETURN,
-		.is_attach_btf = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("fexit/", TRACING,
-		.expected_attach_type = BPF_TRACE_FEXIT,
-		.is_attach_btf = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("fentry.s/", TRACING,
-		.expected_attach_type = BPF_TRACE_FENTRY,
-		.is_attach_btf = true,
-		.is_sleepable = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("fmod_ret.s/", TRACING,
-		.expected_attach_type = BPF_MODIFY_RETURN,
-		.is_attach_btf = true,
-		.is_sleepable = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("fexit.s/", TRACING,
-		.expected_attach_type = BPF_TRACE_FEXIT,
-		.is_attach_btf = true,
-		.is_sleepable = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("freplace/", EXT,
-		.is_attach_btf = true,
-		.attach_fn = attach_trace),
-	SEC_DEF("lsm/", LSM,
-		.is_attach_btf = true,
-		.expected_attach_type = BPF_LSM_MAC,
-		.attach_fn = attach_lsm),
-	SEC_DEF("lsm.s/", LSM,
-		.is_attach_btf = true,
-		.is_sleepable = true,
-		.expected_attach_type = BPF_LSM_MAC,
-		.attach_fn = attach_lsm),
-	SEC_DEF("iter/", TRACING,
-		.expected_attach_type = BPF_TRACE_ITER,
-		.is_attach_btf = true,
-		.attach_fn = attach_iter),
-	SEC_DEF("syscall", SYSCALL,
-		.is_sleepable = true),
+	SEC_DEF("kprobe/",		KPROBE,	0, SEC_NONE, attach_kprobe),
+	SEC_DEF("uprobe/",		KPROBE,	0, SEC_NONE),
+	SEC_DEF("kretprobe/",		KPROBE, 0, SEC_NONE, attach_kprobe),
+	SEC_DEF("uretprobe/",		KPROBE, 0, SEC_NONE),
+	SEC_DEF("classifier",		SCHED_CLS, 0, SEC_NONE),
+	SEC_DEF("tc",			SCHED_CLS, 0, SEC_NONE),
+	SEC_DEF("action",		SCHED_ACT, 0, SEC_NONE),
+	SEC_DEF("tracepoint/",		TRACEPOINT, 0, SEC_NONE, attach_tp),
+	SEC_DEF("tp/",			TRACEPOINT, 0, SEC_NONE, attach_tp),
+	SEC_DEF("raw_tracepoint/",	RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
+	SEC_DEF("raw_tp/",		RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
+	SEC_DEF("tp_btf/",		TRACING, BPF_TRACE_RAW_TP, SEC_ATTACH_BTF, attach_trace),
+	SEC_DEF("fentry/",		TRACING, BPF_TRACE_FENTRY, SEC_ATTACH_BTF, attach_trace),
+	SEC_DEF("fmod_ret/",		TRACING, BPF_MODIFY_RETURN, SEC_ATTACH_BTF, attach_trace),
+	SEC_DEF("fexit/",		TRACING, BPF_TRACE_FEXIT, SEC_ATTACH_BTF, attach_trace),
+	SEC_DEF("fentry.s/",		TRACING, BPF_TRACE_FENTRY, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_trace),
+	SEC_DEF("fmod_ret.s/",		TRACING, BPF_MODIFY_RETURN, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_trace),
+	SEC_DEF("fexit.s/",		TRACING, BPF_TRACE_FEXIT, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_trace),
+	SEC_DEF("freplace/",		EXT, 0, SEC_ATTACH_BTF, attach_trace),
+	SEC_DEF("lsm/",			LSM, BPF_LSM_MAC, SEC_ATTACH_BTF, attach_lsm),
+	SEC_DEF("lsm.s/",		LSM, BPF_LSM_MAC, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_lsm),
+	SEC_DEF("iter/",		TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF, attach_iter),
+	SEC_DEF("syscall",		SYSCALL, 0, SEC_SLEEPABLE),
 	BPF_EAPROG_SEC("xdp_devmap/",		BPF_PROG_TYPE_XDP,
 						BPF_XDP_DEVMAP),
 	BPF_EAPROG_SEC("xdp_cpumap/",		BPF_PROG_TYPE_XDP,
 						BPF_XDP_CPUMAP),
 	BPF_APROG_SEC("xdp",			BPF_PROG_TYPE_XDP,
 						BPF_XDP),
-	BPF_PROG_SEC("perf_event",		BPF_PROG_TYPE_PERF_EVENT),
-	BPF_PROG_SEC("lwt_in",			BPF_PROG_TYPE_LWT_IN),
-	BPF_PROG_SEC("lwt_out",			BPF_PROG_TYPE_LWT_OUT),
-	BPF_PROG_SEC("lwt_xmit",		BPF_PROG_TYPE_LWT_XMIT),
-	BPF_PROG_SEC("lwt_seg6local",		BPF_PROG_TYPE_LWT_SEG6LOCAL),
+	SEC_DEF("perf_event",		PERF_EVENT, 0, SEC_NONE),
+	SEC_DEF("lwt_in",		LWT_IN, 0, SEC_NONE),
+	SEC_DEF("lwt_out",		LWT_OUT, 0, SEC_NONE),
+	SEC_DEF("lwt_xmit",		LWT_XMIT, 0, SEC_NONE),
+	SEC_DEF("lwt_seg6local",	LWT_SEG6LOCAL, 0, SEC_NONE),
 	BPF_APROG_SEC("cgroup_skb/ingress",	BPF_PROG_TYPE_CGROUP_SKB,
 						BPF_CGROUP_INET_INGRESS),
 	BPF_APROG_SEC("cgroup_skb/egress",	BPF_PROG_TYPE_CGROUP_SKB,
 						BPF_CGROUP_INET_EGRESS),
-	BPF_APROG_COMPAT("cgroup/skb",		BPF_PROG_TYPE_CGROUP_SKB),
+	SEC_DEF("cgroup/skb",		CGROUP_SKB, 0, SEC_NONE),
 	BPF_EAPROG_SEC("cgroup/sock_create",	BPF_PROG_TYPE_CGROUP_SOCK,
 						BPF_CGROUP_INET_SOCK_CREATE),
 	BPF_EAPROG_SEC("cgroup/sock_release",	BPF_PROG_TYPE_CGROUP_SOCK,
@@ -8102,7 +8075,7 @@ static const struct bpf_sec_def section_defs[] = {
 						BPF_SK_SKB_STREAM_PARSER),
 	BPF_APROG_SEC("sk_skb/stream_verdict",	BPF_PROG_TYPE_SK_SKB,
 						BPF_SK_SKB_STREAM_VERDICT),
-	BPF_APROG_COMPAT("sk_skb",		BPF_PROG_TYPE_SK_SKB),
+	SEC_DEF("sk_skb",		SK_SKB, 0, SEC_NONE),
 	BPF_APROG_SEC("sk_msg",			BPF_PROG_TYPE_SK_MSG,
 						BPF_SK_MSG_VERDICT),
 	BPF_APROG_SEC("lirc_mode2",		BPF_PROG_TYPE_LIRC_MODE2,
@@ -8139,16 +8112,14 @@ static const struct bpf_sec_def section_defs[] = {
 						BPF_CGROUP_GETSOCKOPT),
 	BPF_EAPROG_SEC("cgroup/setsockopt",	BPF_PROG_TYPE_CGROUP_SOCKOPT,
 						BPF_CGROUP_SETSOCKOPT),
-	BPF_PROG_SEC("struct_ops",		BPF_PROG_TYPE_STRUCT_OPS),
+	SEC_DEF("struct_ops",		STRUCT_OPS, 0, SEC_NONE),
 	BPF_EAPROG_SEC("sk_lookup/",		BPF_PROG_TYPE_SK_LOOKUP,
 						BPF_SK_LOOKUP),
 };
 
 #undef BPF_PROG_SEC_IMPL
-#undef BPF_PROG_SEC
 #undef BPF_APROG_SEC
 #undef BPF_EAPROG_SEC
-#undef BPF_APROG_COMPAT
 #undef SEC_DEF
 
 #define MAX_TYPE_NAME_SIZE 32
@@ -8176,8 +8147,15 @@ static char *libbpf_get_type_names(bool attach_type)
 	buf[0] = '\0';
 	/* Forge string buf with all available names */
 	for (i = 0; i < ARRAY_SIZE(section_defs); i++) {
-		if (attach_type && !section_defs[i].is_attachable)
-			continue;
+		const struct bpf_sec_def *sec_def = &section_defs[i];
+
+		if (attach_type) {
+			if (sec_def->preload_fn != libbpf_preload_prog)
+				continue;
+
+			if (!(sec_def->cookie & SEC_ATTACHABLE))
+				continue;
+		}
 
 		if (strlen(buf) + strlen(section_defs[i].sec) + 2 > len) {
 			free(buf);
@@ -8501,20 +8479,13 @@ static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
 	return -ESRCH;
 }
 
-static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd, int *btf_type_id)
+static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attach_name,
+				     int *btf_obj_fd, int *btf_type_id)
 {
 	enum bpf_attach_type attach_type = prog->expected_attach_type;
 	__u32 attach_prog_fd = prog->attach_prog_fd;
-	const char *attach_name;
 	int err = 0;
 
-	if (!prog->sec_def || !prog->sec_def->is_attach_btf) {
-		pr_warn("failed to identify BTF ID based on ELF section name '%s'\n",
-			prog->sec_name);
-		return -ESRCH;
-	}
-	attach_name = prog->sec_name + strlen(prog->sec_def->sec);
-
 	/* BPF program's BTF ID */
 	if (attach_prog_fd) {
 		err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd);
@@ -8564,7 +8535,9 @@ int libbpf_attach_type_by_name(const char *name,
 		return libbpf_err(-EINVAL);
 	}
 
-	if (!sec_def->is_attachable)
+	if (sec_def->preload_fn != libbpf_preload_prog)
+		return libbpf_err(-EINVAL);
+	if (!(sec_def->cookie & SEC_ATTACHABLE))
 		return libbpf_err(-EINVAL);
 
 	*attach_type = sec_def->expected_attach_type;