Allow kprobe tracepoint events creation through legacy interface, as the
kprobe dynamic PMUs support, used by default, was only created in v4.17.
This enables CO.RE support for older kernels.
Signed-off-by: Rafael David Tinoco <rafaeldtinoco@xxxxxxxxx>
---
tools/lib/bpf/libbpf.c | 125 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 123 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 1e04ce724240..72a22c4d8295 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10007,6 +10007,10 @@ struct bpf_link {
char *pin_path; /* NULL, if not pinned */
int fd; /* hook FD, -1 if not applicable */
bool disconnected;
+ struct {
+ char *name;
+ bool retprobe;
+ } legacy;
};
/* Replace link's underlying BPF program with the new one */
@@ -10143,6 +10147,47 @@ int bpf_link__unpin(struct bpf_link *link)
return 0;
}
+static int poke_kprobe_events(bool add, const char *name, bool retprobe)
+{
+ int fd, ret = 0;
+ char probename[32], cmd[160];
+ const char *file = "/sys/kernel/debug/tracing/kprobe_events";
+
+ memset(probename, 0, sizeof(probename));
+
+ if (retprobe)
+ ret = snprintf(probename, sizeof(probename), "kprobes/%s_ret", name);
+ else
+ ret = snprintf(probename, sizeof(probename), "kprobes/%s", name);
+
+ if (ret <= strlen("kprobes/"))
+ return -EINVAL;
+
+ if (add)
+ snprintf(cmd, sizeof(cmd),"%c:%s %s", retprobe ? 'r' : 'p', probename, name);
+ else
+ snprintf(cmd, sizeof(cmd), "-:%s", probename);
+
+ if (!(fd = open(file, O_WRONLY|O_APPEND, 0)))
+ return -errno;
+ if ((ret = write(fd, cmd, strlen(cmd))) < 0)
+ ret = -errno;
+
+ close(fd);
+
+ return ret;
+}
+
+static inline int add_kprobe_event_legacy(const char* name, bool retprobe)
+{
+ return poke_kprobe_events(true, name, retprobe);
+}
+
+static inline int remove_kprobe_event_legacy(const char* name, bool retprobe)
+{
+ return poke_kprobe_events(false, name, retprobe);
+}
+
static int bpf_link__detach_perf_event(struct bpf_link *link)
{
int err;
@@ -10152,6 +10197,12 @@ static int bpf_link__detach_perf_event(struct bpf_link *link)
err = -errno;
close(link->fd);
+
+ if (link->legacy.name) {
+ remove_kprobe_event_legacy(link->legacy.name, link->legacy.retprobe);
+ free(link->legacy.name);
+ }
+
return libbpf_err(err);
}
@@ -10229,6 +10280,23 @@ 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)
+{
+ char file[96];
+ const char *fname = "/sys/kernel/debug/tracing/events/kprobes/%s/id";
+
+ snprintf(file, sizeof(file), fname, func_name);
+
+ 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";
@@ -10304,6 +10372,43 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
return pfd;
}
+static int perf_event_open_probe_legacy(bool uprobe, bool retprobe, const char *name,
+ uint64_t offset, int pid)
+{
+ struct perf_event_attr attr = {};
+ char errmsg[STRERR_BUFSIZE];
+ int type, pfd, err;
+
+ if (uprobe) // unsupported
+ return -EINVAL;
+
+ if ((err = add_kprobe_event_legacy(name, retprobe)) < 0) {
+ pr_warn("failed to add legacy kprobe event: %s\n",
+ libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+ return err;
+ }
+ if ((type = determine_kprobe_perf_type_legacy(name)) < 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(struct bpf_program *prog,
bool retprobe,
const char *func_name)
@@ -10311,9 +10416,18 @@ struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
char errmsg[STRERR_BUFSIZE];
struct bpf_link *link;
int pfd, err;
+ bool legacy = false;
- pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
- 0 /* offset */, -1 /* pid */);
+ if (!(legacy = determine_kprobe_legacy()))
+ pfd = perf_event_open_probe(false /* uprobe */,
+ retprobe, func_name,
+ 0 /* offset */,
+ -1 /* pid */);
+ else
+ pfd = perf_event_open_probe_legacy(false /* uprobe */,
+ 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,
@@ -10329,6 +10443,13 @@ struct bpf_link *bpf_program__attach_kprobe(struct bpf_program *prog,
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
return libbpf_err_ptr(err);
}
+
+ if (legacy) {
+ /* needed history for the legacy probe cleanup */
+ link->legacy.name = strdup(func_name);
+ link->legacy.retprobe = retprobe;
+ }
+
return link;
}
--
2.27.0
