Allow kprobe tracepoint events creation through legacy interface, as the
kprobe dynamic PMUs support, used by default, was only created in v4.17.
After commit "bpf: implement minimal BPF perf link", it was allowed that
some extra - to the link - information is accessed through container_of
struct bpf_link. This allows the tracing perf event legacy name, and
information whether it is a retprobe, to be saved outside bpf_link
structure, which would not be optimal.
This enables CO.RE support for older kernels.
Cc: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Signed-off-by: Rafael David Tinoco <rafaeldtinoco@xxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 127 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 125 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e1b7b2b6618c..40037340a3e7 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8985,9 +8985,55 @@ 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[192] = {}, 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+%lu", name, 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;
+ char *legacy_name;
+ bool is_retprobe;
};
static int bpf_link_perf_detach(struct bpf_link *link)
@@ -9002,6 +9048,10 @@ static int bpf_link_perf_detach(struct bpf_link *link)
close(perf_link->perf_event_fd);
close(link->fd);
+ /* legacy kprobe needs to be removed after perf event fd closure */
+ if (perf_link->legacy_name)
+ remove_kprobe_event_legacy(perf_link->legacy_name, perf_link->is_retprobe);
+
return libbpf_err(err);
}
@@ -9009,6 +9059,9 @@ static void bpf_link_perf_dealloc(struct bpf_link *link)
{
struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
+ if (perf_link->legacy_name)
+ free(perf_link->legacy_name);
+
free(perf_link);
}
@@ -9122,6 +9175,26 @@ static int parse_uint_from_file(const char *file, const char *fmt)
return ret;
}
+static bool determine_kprobe_legacy(void)
+{
+ const char *file = "/sys/bus/event_source/devices/kprobe/type";
+
+ return access(file, 0) == 0 ? false : true;
+}
+
+static int determine_kprobe_perf_type_legacy(const char *func_name, bool is_retprobe)
+{
+ char file[192];
+
+ const char *fname = "/sys/kernel/debug/tracing/events/%s/%s_libbpf_%d/id";
+
+ snprintf(file, sizeof(file), fname,
+ 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";
@@ -9197,6 +9270,41 @@ 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)
+{
+ struct perf_event_attr attr = {};
+ char errmsg[STRERR_BUFSIZE];
+ int type, pfd, err;
+
+ err = add_kprobe_event_legacy(name, retprobe, offset);
+ if (err < 0) {
+ pr_warn("failed to add legacy kprobe event: %s\n",
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ return err;
+ }
+ type = determine_kprobe_perf_type_legacy(name, retprobe);
+ if (type < 0) {
+ pr_warn("failed to determine legacy kprobe event id: %s\n",
+ libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
+ return type;
+ }
+ attr.size = sizeof(attr);
+ attr.config = type;
+ attr.type = PERF_TYPE_TRACEPOINT;
+
+ pfd = syscall(__NR_perf_event_open, &attr,
+ pid < 0 ? -1 : pid, /* pid */
+ pid == -1 ? 0 : -1, /* cpu */
+ -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
+ if (pfd < 0) {
+ err = -errno;
+ pr_warn("legacy kprobe perf_event_open() failed: %s\n",
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ return err;
+ }
+ return pfd;
+}
+
struct bpf_link *
bpf_program__attach_kprobe_opts(struct bpf_program *prog,
const char *func_name,
@@ -9208,6 +9316,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
unsigned long offset;
bool retprobe;
int pfd, err;
+ bool legacy;
if (!OPTS_VALID(opts, bpf_kprobe_opts))
return libbpf_err_ptr(-EINVAL);
@@ -9216,8 +9325,16 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
offset = OPTS_GET(opts, offset, 0);
pe_opts.user_ctx = OPTS_GET(opts, user_ctx, 0);
- pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
- offset, -1 /* pid */);
+ legacy = determine_kprobe_legacy();
+ if (!legacy) {
+ pfd = perf_event_open_probe(false /* uprobe */,
+ retprobe, func_name,
+ offset, -1 /* pid */);
+ } else {
+ pfd = perf_event_kprobe_open_legacy(retprobe, func_name,
+ 0 /* offset */,
+ -1 /* pid */);
+ }
if (pfd < 0) {
pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
prog->name, retprobe ? "kretprobe" : "kprobe", func_name,
@@ -9233,6 +9350,12 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
return libbpf_err_ptr(err);
}
+ if (legacy) {
+ struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
+ perf_link->legacy_name = strdup(func_name);
+ perf_link->is_retprobe = retprobe;
+ }
+
return link;
}
--
2.30.2
