On Mon, Jul 1, 2019 at 10:09 AM Yonghong Song [off-list ref] wrote:

On 6/28/19 8:49 PM, Andrii Nakryiko wrote:

quoted

Add ability to attach to kernel and user probes and retprobes.
Implementation depends on perf event support for kprobes/uprobes.

Signed-off-by: Andrii Nakryiko <redacted>
---
  tools/lib/bpf/libbpf.c   | 165 +++++++++++++++++++++++++++++++++++++++
  tools/lib/bpf/libbpf.h   |   7 ++
  tools/lib/bpf/libbpf.map |   2 +
  3 files changed, 174 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 98c155ec3bfa..2f79e9563db9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c

@@ -4019,6 +4019,171 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog,
      return (struct bpf_link *)link;
  }

+static int parse_value_from_file(const char *file, const char *fmt)

Here, the value from the file must be positive int values to avoid
confusion between valid value vs. error code.
Could you add a comment to state this fact for the current
uprobe/kprobe/tracepoint support?

You are right. I'll name it parse_uint_from_file to make it more
obvious (though even that is not strictly true, we expect value in the
range of [0, 2^32-1]. I'll leave a comment.

quoted

+{
+     char buf[STRERR_BUFSIZE];
+     int err, ret;
+     FILE *f;
+
+     f = fopen(file, "r");
+     if (!f) {
+             err = -errno;
+             pr_debug("failed to open '%s': %s\n", file,
+                      libbpf_strerror_r(err, buf, sizeof(buf)));
+             fclose(f);

fclose(f) is not needed. fopen has failed.

*facepalm*, of course, thanks!

quoted

+             return err;
+     }
+     err = fscanf(f, fmt, &ret);
+     if (err != 1) {
+             err = err == EOF ? -EIO : -errno;
+             pr_debug("failed to parse '%s': %s\n", file,
+                     libbpf_strerror_r(err, buf, sizeof(buf)));
+             fclose(f);
+             return err;
+     }
+     fclose(f);
+     return ret;
+}
+
+static int determine_kprobe_perf_type(void)
+{
+     const char *file = "/sys/bus/event_source/devices/kprobe/type";
+
+     return parse_value_from_file(file, "%d\n");
+}
+
+static int determine_uprobe_perf_type(void)
+{
+     const char *file = "/sys/bus/event_source/devices/uprobe/type";
+
+     return parse_value_from_file(file, "%d\n");
+}
+
+static int determine_kprobe_retprobe_bit(void)
+{
+     const char *file = "/sys/bus/event_source/devices/kprobe/format/retprobe";
+
+     return parse_value_from_file(file, "config:%d\n");
+}
+
+static int determine_uprobe_retprobe_bit(void)
+{
+     const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";
+
+     return parse_value_from_file(file, "config:%d\n");
+}
+
+static int perf_event_open_probe(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;
+
+     type = uprobe ? determine_uprobe_perf_type()
+                   : determine_kprobe_perf_type();
+     if (type < 0) {
+             pr_warning("failed to determine %s perf type: %s\n",
+                        uprobe ? "uprobe" : "kprobe",
+                        libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
+             return type;
+     }
+     if (retprobe) {
+             int bit = uprobe ? determine_uprobe_retprobe_bit()
+                              : determine_kprobe_retprobe_bit();
+
+             if (bit < 0) {
+                     pr_warning("failed to determine %s retprobe bit: %s\n",
+                                uprobe ? "uprobe" : "kprobe",
+                                libbpf_strerror_r(bit, errmsg,
+                                                  sizeof(errmsg)));
+                     return bit;
+             }
+             attr.config |= 1 << bit;
+     }
+     attr.size = sizeof(attr);
+     attr.type = type;
+     attr.config1 = (uint64_t)(void *)name; /* kprobe_func or uprobe_path */
+     attr.config2 = offset;                 /* kprobe_addr or probe_offset */
+
+     /* pid filter is meaningful only for uprobes */
+     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_warning("%s perf_event_open() failed: %s\n",
+                        uprobe ? "uprobe" : "kprobe",
+                        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)
+{
+     char errmsg[STRERR_BUFSIZE];
+     struct bpf_link *link;
+     int pfd, err;
+
+     pfd = perf_event_open_probe(false /* uprobe */, retprobe, func_name,
+                                 0 /* offset */, -1 /* pid */);
+     if (pfd < 0) {
+             pr_warning("program '%s': failed to create %s '%s' perf event: %s\n",
+                        bpf_program__title(prog, false),
+                        retprobe ? "kretprobe" : "kprobe", func_name,
+                        libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+             return ERR_PTR(pfd);
+     }
+     link = bpf_program__attach_perf_event(prog, pfd);
+     if (IS_ERR(link)) {
+             close(pfd);
+             err = PTR_ERR(link);
+             pr_warning("program '%s': failed to attach to %s '%s': %s\n",
+                        bpf_program__title(prog, false),
+                        retprobe ? "kretprobe" : "kprobe", func_name,
+                        libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+             return link;
+     }
+     return link;
+}
+
+struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,
+                                         bool retprobe, pid_t pid,
+                                         const char *binary_path,
+                                         size_t func_offset)
+{
+     char errmsg[STRERR_BUFSIZE];
+     struct bpf_link *link;
+     int pfd, err;
+
+     pfd = perf_event_open_probe(true /* uprobe */, retprobe,
+                                 binary_path, func_offset, pid);
+     if (pfd < 0) {
+             pr_warning("program '%s': failed to create %s '%s:0x%zx' perf event: %s\n",
+                        bpf_program__title(prog, false),
+                        retprobe ? "uretprobe" : "uprobe",
+                        binary_path, func_offset,
+                        libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
+             return ERR_PTR(pfd);
+     }
+     link = bpf_program__attach_perf_event(prog, pfd);
+     if (IS_ERR(link)) {
+             close(pfd);
+             err = PTR_ERR(link);
+             pr_warning("program '%s': failed to attach to %s '%s:0x%zx': %s\n",
+                        bpf_program__title(prog, false),
+                        retprobe ? "uretprobe" : "uprobe",
+                        binary_path, func_offset,
+                        libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+             return link;
+     }
+     return link;
+}
+
  enum bpf_perf_event_ret
  bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
                         void **copy_mem, size_t *copy_size,

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 1bf66c4a9330..bd767cc11967 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h

@@ -171,6 +171,13 @@ LIBBPF_API int bpf_link__destroy(struct bpf_link *link);

  LIBBPF_API struct bpf_link *
  bpf_program__attach_perf_event(struct bpf_program *prog, int pfd);
+LIBBPF_API struct bpf_link *
+bpf_program__attach_kprobe(struct bpf_program *prog, bool retprobe,
+                        const char *func_name);
+LIBBPF_API struct bpf_link *
+bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
+                        pid_t pid, const char *binary_path,
+                        size_t func_offset);

  struct bpf_insn;

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 756f5aa802e9..57a40fb60718 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map

@@ -169,7 +169,9 @@ LIBBPF_0.0.4 {
      global:
              bpf_link__destroy;
              bpf_object__load_xattr;
+             bpf_program__attach_kprobe;
              bpf_program__attach_perf_event;
+             bpf_program__attach_uprobe;
              btf_dump__dump_type;
              btf_dump__free;
              btf_dump__new;