libbpf: Add support to set kprobe/uprobe attach mode

By default, libbpf will attach the kprobe/uprobe BPF program in the
latest mode that supported by kernel. In this patch, we add the support
to let users manually attach kprobe/uprobe in legacy or perf mode.

There are 3 mode that supported by the kernel to attach kprobe/uprobe:

  LEGACY: create perf event in legacy way and don't use bpf_link
  PERF: create perf event with perf_event_open() and don't use bpf_link

Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Biao Jiang <benbjiang@tencent.com>
Link: create perf event with perf_event_open() and use bpf_link
Link: https://lore.kernel.org/bpf/20230113093427.1666466-1-imagedong@tencent.com/
Link: https://lore.kernel.org/bpf/20230306064833.7932-2-imagedong@tencent.com
Users now can manually choose the mode with
bpf_program__attach_uprobe_opts()/bpf_program__attach_kprobe_opts().

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index dacaae31b76a5411f03819fa0f8fbe2b8f0b20a1..a557718401e4c41b5890137e82d0dcbaf48b9c95 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9724,6 +9724,7 @@ struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *p
        char errmsg[STRERR_BUFSIZE];
        struct bpf_link_perf *link;
        int prog_fd, link_fd = -1, err;
+       bool force_ioctl_attach;
 
        if (!OPTS_VALID(opts, bpf_perf_event_opts))
                return libbpf_err_ptr(-EINVAL);
@@ -9747,7 +9748,8 @@ struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *p
        link->link.dealloc = &bpf_link_perf_dealloc;
        link->perf_event_fd = pfd;
 
-       if (kernel_supports(prog->obj, FEAT_PERF_LINK)) {
+       force_ioctl_attach = OPTS_GET(opts, force_ioctl_attach, false);
+       if (kernel_supports(prog->obj, FEAT_PERF_LINK) && !force_ioctl_attach) {
                DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts,
                        .perf_event.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0));
 
@@ -10106,6 +10108,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
                                const struct bpf_kprobe_opts *opts)
 {
        DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
+       enum probe_attach_mode attach_mode;
        char errmsg[STRERR_BUFSIZE];
        char *legacy_probe = NULL;
        struct bpf_link *link;
@@ -10116,11 +10119,32 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
        if (!OPTS_VALID(opts, bpf_kprobe_opts))
                return libbpf_err_ptr(-EINVAL);
 
+       attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
        retprobe = OPTS_GET(opts, retprobe, false);
        offset = OPTS_GET(opts, offset, 0);
        pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
 
        legacy = determine_kprobe_perf_type() < 0;
+       switch (attach_mode) {
+       case PROBE_ATTACH_MODE_LEGACY:
+               legacy = true;
+               pe_opts.force_ioctl_attach = true;
+               break;
+       case PROBE_ATTACH_MODE_PERF:
+               if (legacy)
+                       return libbpf_err_ptr(-ENOTSUP);
+               pe_opts.force_ioctl_attach = true;
+               break;
+       case PROBE_ATTACH_MODE_LINK:
+               if (legacy || !kernel_supports(prog->obj, FEAT_PERF_LINK))
+                       return libbpf_err_ptr(-ENOTSUP);
+               break;
+       case PROBE_ATTACH_MODE_DEFAULT:
+               break;
+       default:
+               return libbpf_err_ptr(-EINVAL);
+       }
+
        if (!legacy) {
                pfd = perf_event_open_probe(false /* uprobe */, retprobe,
                                            func_name, offset,
@@ -10852,6 +10876,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
        const char *archive_path = NULL, *archive_sep = NULL;
        char errmsg[STRERR_BUFSIZE], *legacy_probe = NULL;
        DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
+       enum probe_attach_mode attach_mode;
        char full_path[PATH_MAX];
        struct bpf_link *link;
        size_t ref_ctr_off;
@@ -10862,6 +10887,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
        if (!OPTS_VALID(opts, bpf_uprobe_opts))
                return libbpf_err_ptr(-EINVAL);
 
+       attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
        retprobe = OPTS_GET(opts, retprobe, false);
        ref_ctr_off = OPTS_GET(opts, ref_ctr_offset, 0);
        pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
@@ -10903,6 +10929,26 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
        }
 
        legacy = determine_uprobe_perf_type() < 0;
+       switch (attach_mode) {
+       case PROBE_ATTACH_MODE_LEGACY:
+               legacy = true;
+               pe_opts.force_ioctl_attach = true;
+               break;
+       case PROBE_ATTACH_MODE_PERF:
+               if (legacy)
+                       return libbpf_err_ptr(-ENOTSUP);
+               pe_opts.force_ioctl_attach = true;
+               break;
+       case PROBE_ATTACH_MODE_LINK:
+               if (legacy || !kernel_supports(prog->obj, FEAT_PERF_LINK))
+                       return libbpf_err_ptr(-ENOTSUP);
+               break;
+       case PROBE_ATTACH_MODE_DEFAULT:
+               break;
+       default:
+               return libbpf_err_ptr(-EINVAL);
+       }
+
        if (!legacy) {
                pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,
                                            func_offset, pid, ref_ctr_off);

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 2efd80f6f7b924ebcf8c82673144e4e0c4ea02f6..db4992a036f8b6ea00ccf5ae72ef7fc9b58726ed 100644 (file)
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -447,12 +447,15 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach(const struct bpf_program *prog);
 
 struct bpf_perf_event_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
        /* custom user-provided value fetchable through bpf_get_attach_cookie() */
        __u64 bpf_cookie;
+       /* don't use BPF link when attach BPF program */
+       bool force_ioctl_attach;
+       size_t :0;
 };
-#define bpf_perf_event_opts__last_field bpf_cookie
+#define bpf_perf_event_opts__last_field force_ioctl_attach
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event(const struct bpf_program *prog, int pfd);
@@ -461,8 +464,25 @@ LIBBPF_API struct bpf_link *
 bpf_program__attach_perf_event_opts(const struct bpf_program *prog, int pfd,
                                    const struct bpf_perf_event_opts *opts);
 
+/**
+ * enum probe_attach_mode - the mode to attach kprobe/uprobe
+ *
+ * force libbpf to attach kprobe/uprobe in specific mode, -ENOTSUP will
+ * be returned if it is not supported by the kernel.
+ */
+enum probe_attach_mode {
+       /* attach probe in latest supported mode by kernel */
+       PROBE_ATTACH_MODE_DEFAULT = 0,
+       /* attach probe in legacy mode, using debugfs/tracefs */
+       PROBE_ATTACH_MODE_LEGACY,
+       /* create perf event with perf_event_open() syscall */
+       PROBE_ATTACH_MODE_PERF,
+       /* attach probe with BPF link */
+       PROBE_ATTACH_MODE_LINK,
+};
+
 struct bpf_kprobe_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
        /* custom user-provided value fetchable through bpf_get_attach_cookie() */
        __u64 bpf_cookie;
@@ -470,9 +490,11 @@ struct bpf_kprobe_opts {
        size_t offset;
        /* kprobe is return probe */
        bool retprobe;
+       /* kprobe attach mode */
+       enum probe_attach_mode attach_mode;
        size_t :0;
 };
-#define bpf_kprobe_opts__last_field retprobe
+#define bpf_kprobe_opts__last_field attach_mode
 
 LIBBPF_API struct bpf_link *
 bpf_program__attach_kprobe(const struct bpf_program *prog, bool retprobe,
@@ -506,7 +528,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
                                      const struct bpf_kprobe_multi_opts *opts);
 
 struct bpf_ksyscall_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
        /* custom user-provided value fetchable through bpf_get_attach_cookie() */
        __u64 bpf_cookie;
@@ -552,7 +574,7 @@ bpf_program__attach_ksyscall(const struct bpf_program *prog,
                             const struct bpf_ksyscall_opts *opts);
 
 struct bpf_uprobe_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
        /* offset of kernel reference counted USDT semaphore, added in
         * a6ca88b241d5 ("trace_uprobe: support reference counter in fd-based uprobe")
@@ -570,9 +592,11 @@ struct bpf_uprobe_opts {
         * binary_path.
         */
        const char *func_name;
+       /* uprobe attach mode */
+       enum probe_attach_mode attach_mode;
        size_t :0;
 };
-#define bpf_uprobe_opts__last_field func_name
+#define bpf_uprobe_opts__last_field attach_mode
 
 /**
  * @brief **bpf_program__attach_uprobe()** attaches a BPF program
@@ -646,7 +670,7 @@ bpf_program__attach_usdt(const struct bpf_program *prog,
                         const struct bpf_usdt_opts *opts);
 
 struct bpf_tracepoint_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
        /* custom user-provided value fetchable through bpf_get_attach_cookie() */
        __u64 bpf_cookie;
@@ -1110,7 +1134,7 @@ struct user_ring_buffer;
 typedef int (*ring_buffer_sample_fn)(void *ctx, void *data, size_t size);
 
 struct ring_buffer_opts {
-       size_t sz; /* size of this struct, for forward/backward compatiblity */
+       size_t sz; /* size of this struct, for forward/backward compatibility */
 };
 
 #define ring_buffer_opts__last_field sz
@@ -1475,7 +1499,7 @@ LIBBPF_API void
 bpf_object__destroy_subskeleton(struct bpf_object_subskeleton *s);
 
 struct gen_loader_opts {
-       size_t sz; /* size of this struct, for forward/backward compatiblity */
+       size_t sz; /* size of this struct, for forward/backward compatibility */
        const char *data;
        const char *insns;
        __u32 data_sz;
@@ -1493,13 +1517,13 @@ enum libbpf_tristate {
 };
 
 struct bpf_linker_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
 };
 #define bpf_linker_opts__last_field sz
 
 struct bpf_linker_file_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
 };
 #define bpf_linker_file_opts__last_field sz
@@ -1542,7 +1566,7 @@ typedef int (*libbpf_prog_attach_fn_t)(const struct bpf_program *prog, long cook
                                       struct bpf_link **link);
 
 struct libbpf_prog_handler_opts {
-       /* size of this struct, for forward/backward compatiblity */
+       /* size of this struct, for forward/backward compatibility */
        size_t sz;
        /* User-provided value that is passed to prog_setup_fn,
         * prog_prepare_load_fn, and prog_attach_fn callbacks. Allows user to