On Wed, Jul 14, 2021 at 2:45 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> From: Alan Maguire <alan.maguire@xxxxxxxxxx>
>
> 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.
>
> [jolsa: changed original code to use bpf_program__attach_kprobe_opts
> and use dynamic allocation in sscanf]
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 24 ++++++++++++++++++++++--
> 1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index d93a6f9408d1..abe6d4842bb0 100644
> --- 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);
could have used %li here to support both +0xabc and +123 forms
> + 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;
leaking func here
> + 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,
> --
> 2.31.1
>
