libbpf: Allow specification of "kprobe/function+offset"

kprobes can be placed on most instructions in a function, not
just entry, and ftrace and bpftrace support the function+offset
notification for probe placement.  Adding parsing of func_name
into func+offset to bpf_program__attach_kprobe() allows the
user to specify

SEC("kprobe/bpf_fentry_test5+0x6")

...for example, and the offset can be passed to perf_event_open_probe()
to support kprobe attachment.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210714094400.396467-8-jolsa@kernel.org

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d93a6f9..abe6d48 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10348,6 +10348,7 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
 
 struct bpf_program_attach_kprobe_opts {
        bool retprobe;
+       unsigned long offset;
 };
 
 static struct bpf_link*
@@ -10360,7 +10361,7 @@ bpf_program__attach_kprobe_opts(struct bpf_program *prog,
        int pfd, err;
 
        pfd = perf_event_open_probe(false /* uprobe */, opts->retprobe, func_name,
-                                   0 /* offset */, -1 /* pid */);
+                                   opts->offset, -1 /* pid */);
        if (pfd < 0) {
                pr_warn("prog '%s': failed to create %s '%s' perf event: %s\n",
                        prog->name, opts->retprobe ? "kretprobe" : "kprobe", func_name,
@@ -10394,12 +10395,31 @@ static struct bpf_link *attach_kprobe(const struct bpf_sec_def *sec,
                                      struct bpf_program *prog)
 {
        struct bpf_program_attach_kprobe_opts opts;
+       unsigned long offset = 0;
+       struct bpf_link *link;
        const char *func_name;
+       char *func;
+       int n, err;
 
        func_name = prog->sec_name + sec->len;
        opts.retprobe = strcmp(sec->sec, "kretprobe/") == 0;
 
-       return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
+       n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%lx", &func, &offset);
+       if (n < 1) {
+               err = -EINVAL;
+               pr_warn("kprobe name is invalid: %s\n", func_name);
+               return libbpf_err_ptr(err);
+       }
+       if (opts.retprobe && offset != 0) {
+               err = -EINVAL;
+               pr_warn("kretprobes do not support offset specification\n");
+               return libbpf_err_ptr(err);
+       }
+
+       opts.offset = offset;
+       link = bpf_program__attach_kprobe_opts(prog, func, &opts);
+       free(func);
+       return link;
 }
 
 struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,