Commit 46ed5fc3 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: Refactor and simplify legacy kprobe code 



Refactor legacy kprobe handling code to follow the same logic as uprobe
legacy logic added in the next patchs:
  - add append_to_file() helper that makes it simpler to work with
    tracefs file-based interface for creating and deleting probes;
  - move out probe/event name generation outside of the code that
    adds/removes it, which simplifies bookkeeping significantly;
  - change the probe name format to start with "libbpf_" prefix and
    include offset within kernel function;
  - switch 'unsigned long' to 'size_t' for specifying kprobe offsets,
    which is consistent with how uprobes define that, simplifies
    printf()-ing internally, and also avoids unnecessary complications on
    architectures where sizeof(long) != sizeof(void *).

This patch also implicitly fixes the problem with invalid open() error
handling present in poke_kprobe_events(), which (the function) this
patch removes.

Fixes: ca304b40 ("libbpf: Introduce legacy kprobe events support")
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210921210036.1545557-4-andrii@kernel.org
parent d3b0e3b0

tools/lib/bpf/libbpf.c

+87 −72
Original line number Diff line number Diff line
@@ -9011,59 +9011,17 @@ int bpf_link__unpin(struct bpf_link *link) 
	return 0;

}



static int poke_kprobe_events(bool add, const char *name, bool retprobe, uint64_t offset)

{

	int fd, ret = 0;

	pid_t p = getpid();

	char cmd[260], probename[128], probefunc[128];

	const char *file = "/sys/kernel/debug/tracing/kprobe_events";



	if (retprobe)

		snprintf(probename, sizeof(probename), "kretprobes/%s_libbpf_%u", name, p);

	else

		snprintf(probename, sizeof(probename), "kprobes/%s_libbpf_%u", name, p);



	if (offset)

		snprintf(probefunc, sizeof(probefunc), "%s+%zu", name, (size_t)offset);



	if (add) {

		snprintf(cmd, sizeof(cmd), "%c:%s %s",

			 retprobe ? 'r' : 'p',

			 probename,

			 offset ? probefunc : name);

	} else {

		snprintf(cmd, sizeof(cmd), "-:%s", probename);

	}



	fd = open(file, O_WRONLY | O_APPEND, 0);

	if (!fd)

		return -errno;

	ret = write(fd, cmd, strlen(cmd));

	if (ret < 0)

		ret = -errno;

	close(fd);



	return ret;

}



static inline int add_kprobe_event_legacy(const char *name, bool retprobe, uint64_t offset)

{

	return poke_kprobe_events(true, name, retprobe, offset);

}



static inline int remove_kprobe_event_legacy(const char *name, bool retprobe)

{

	return poke_kprobe_events(false, name, retprobe, 0);

}



struct bpf_link_perf {

	struct bpf_link link;

	int perf_event_fd;

	/* legacy kprobe support: keep track of probe identifier and type */

	char *legacy_probe_name;

	bool legacy_is_kprobe;

	bool legacy_is_retprobe;

};



static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe);



static int bpf_link_perf_detach(struct bpf_link *link)

{

	struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
@@ -9077,9 +9035,12 @@ static int bpf_link_perf_detach(struct bpf_link *link) 
	close(link->fd);



	/* legacy kprobe needs to be removed after perf event fd closure */

	if (perf_link->legacy_probe_name)

	if (perf_link->legacy_probe_name) {

		if (perf_link->legacy_is_kprobe) {

			err = remove_kprobe_event_legacy(perf_link->legacy_probe_name,

							 perf_link->legacy_is_retprobe);

		}

	}



	return err;

}
@@ -9202,18 +9163,6 @@ static int parse_uint_from_file(const char *file, const char *fmt) 
	return ret;

}



static int determine_kprobe_perf_type_legacy(const char *func_name, bool is_retprobe)

{

	char file[192];



	snprintf(file, sizeof(file),

		 "/sys/kernel/debug/tracing/events/%s/%s_libbpf_%d/id",

		 is_retprobe ? "kretprobes" : "kprobes",

		 func_name, getpid());



	return parse_uint_from_file(file, "%d\n");

}



static int determine_kprobe_perf_type(void)

{

	const char *file = "/sys/bus/event_source/devices/kprobe/type";
@@ -9296,21 +9245,79 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name, 
	return pfd;

}



static int perf_event_kprobe_open_legacy(bool retprobe, const char *name, uint64_t offset, int pid)

static int append_to_file(const char *file, const char *fmt, ...)

{

	int fd, n, err = 0;

	va_list ap;



	fd = open(file, O_WRONLY | O_APPEND, 0);

	if (fd < 0)

		return -errno;



	va_start(ap, fmt);

	n = vdprintf(fd, fmt, ap);

	va_end(ap);



	if (n < 0)

		err = -errno;



	close(fd);

	return err;

}



static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,

					 const char *kfunc_name, size_t offset)

{

	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), kfunc_name, offset);

}



static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,

				   const char *kfunc_name, size_t offset)

{

	const char *file = "/sys/kernel/debug/tracing/kprobe_events";



	return append_to_file(file, "%c:%s/%s %s+0x%zx",

			      retprobe ? 'r' : 'p',

			      retprobe ? "kretprobes" : "kprobes",

			      probe_name, kfunc_name, offset);

}



static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe)

{

	const char *file = "/sys/kernel/debug/tracing/kprobe_events";



	return append_to_file(file, "-:%s/%s", retprobe ? "kretprobes" : "kprobes", probe_name);

}



static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retprobe)

{

	char file[256];



	snprintf(file, sizeof(file),

		 "/sys/kernel/debug/tracing/events/%s/%s/id",

		 retprobe ? "kretprobes" : "kprobes", probe_name);



	return parse_uint_from_file(file, "%d\n");

}



static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,

					 const char *kfunc_name, size_t offset, int pid)

{

	struct perf_event_attr attr = {};

	char errmsg[STRERR_BUFSIZE];

	int type, pfd, err;



	err = add_kprobe_event_legacy(name, retprobe, offset);

	err = add_kprobe_event_legacy(probe_name, retprobe, kfunc_name, offset);

	if (err < 0) {

		pr_warn("failed to add legacy kprobe event: %s\n",

		pr_warn("failed to add legacy kprobe event for '%s+0x%zx': %s\n",

			kfunc_name, offset,

			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		return err;

	}

	type = determine_kprobe_perf_type_legacy(name, retprobe);

	type = determine_kprobe_perf_type_legacy(probe_name, retprobe);

	if (type < 0) {

		pr_warn("failed to determine legacy kprobe event id: %s\n",

		pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",

			kfunc_name, offset,

			libbpf_strerror_r(type, errmsg, sizeof(errmsg)));

		return type;

	}
@@ -9340,7 +9347,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, 
	char errmsg[STRERR_BUFSIZE];

	char *legacy_probe = NULL;

	struct bpf_link *link;

	unsigned long offset;

	size_t offset;

	bool retprobe, legacy;

	int pfd, err;
@@ -9357,17 +9364,23 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, 
					    func_name, offset,

					    -1 /* pid */, 0 /* ref_ctr_off */);

	} else {

		char probe_name[256];



		gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name),

					     func_name, offset);



		legacy_probe = strdup(func_name);

		if (!legacy_probe)

			return libbpf_err_ptr(-ENOMEM);



		pfd = perf_event_kprobe_open_legacy(retprobe, func_name,

		pfd = perf_event_kprobe_open_legacy(legacy_probe, retprobe, func_name,

						    offset, -1 /* pid */);

	}

	if (pfd < 0) {

		err = pfd;

		pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",

			prog->name, retprobe ? "kretprobe" : "kprobe", func_name,

		err = -errno;

		pr_warn("prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n",

			prog->name, retprobe ? "kretprobe" : "kprobe",

			func_name, offset,

			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		goto err_out;

	}
@@ -9375,8 +9388,9 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, 
	err = libbpf_get_error(link);

	if (err) {

		close(pfd);

		pr_warn("prog '%s': failed to attach to %s '%s': %s\n",

			prog->name, retprobe ? "kretprobe" : "kprobe", func_name,

		pr_warn("prog '%s': failed to attach to %s '%s+0x%zx': %s\n",

			prog->name, retprobe ? "kretprobe" : "kprobe",

			func_name, offset,

			libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		goto err_out;

	}
@@ -9384,6 +9398,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog, 
		struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);



		perf_link->legacy_probe_name = legacy_probe;

		perf_link->legacy_is_kprobe = true;

		perf_link->legacy_is_retprobe = retprobe;

	}

tools/lib/bpf/libbpf.h

+1 −1
Original line number Diff line number Diff line
@@ -269,7 +269,7 @@ struct bpf_kprobe_opts { 
	/* custom user-provided value fetchable through bpf_get_attach_cookie() */

	__u64 bpf_cookie;

	/* function's offset to install kprobe to */

	unsigned long offset;

	size_t offset;

	/* kprobe is return probe */

	bool retprobe;

	size_t :0;