Re: [PATCH 6/8] libbpf: Add bpf_program__attach_kprobe_opts for multi kprobes

[Jiri Olsa]

On Mon, Feb 07, 2022 at 10:59:29AM -0800, Andrii Nakryiko wrote:

SNIP

> > +struct fprobe_resolve {
> > +       const char *name;
> > +       __u64 *addrs;
> > +       __u32 alloc;
> > +       __u32 cnt;
> > +};
> > +
> > +static bool glob_matches(const char *glob, const char *s)
> 
> we've since added more generic glob_match() implementation (see
> test_progs.c), let's copy/paste that one (it's actually shorter and
> doesn't do hacky input args modification). Let's maybe also add '?'
> handling (it's trivial). Both original code in perf and the one in
> test_progs.c are GPL-2.0-only, so let's also get acks from original
> authors.

ok, will check

> 
> > +{
> > +       int n = strlen(glob);
> > +
> > +       if (n == 1 && glob[0] == '*')
> > +               return true;
> > +
> > +       if (glob[0] == '*' && glob[n - 1] == '*') {
> > +               const char *subs;
> > +               /* substring match */
> > +
> > +               /* this is hacky, but we don't want to allocate
> > +                * for no good reason
> > +                */
> > +               ((char *)glob)[n - 1] = '\0';
> > +               subs = strstr(s, glob + 1);
> > +               ((char *)glob)[n - 1] = '*';
> > +
> > +               return subs != NULL;
> > +       } else if (glob[0] == '*') {
> > +               size_t nn = strlen(s);
> > +               /* suffix match */
> > +
> > +               /* too short for a given suffix */
> > +               if (nn < n - 1)
> > +                       return false;
> > +               return strcmp(s + nn - (n - 1), glob + 1) == 0;
> > +       } else if (glob[n - 1] == '*') {
> > +               /* prefix match */
> > +               return strncmp(s, glob, n - 1) == 0;
> > +       } else {
> > +               /* exact match */
> > +               return strcmp(glob, s) == 0;
> > +       }
> > +}
> > +
> > +static int resolve_fprobe_cb(void *arg, unsigned long long sym_addr,
> > +                            char sym_type, const char *sym_name)
> > +{
> > +       struct fprobe_resolve *res = arg;
> > +       __u64 *p;
> > +
> > +       if (!glob_matches(res->name, sym_name))
> > +               return 0;
> > +
> > +       if (res->cnt == res->alloc) {
> > +               res->alloc = max((__u32) 16, res->alloc * 3 / 2);
> > +               p = libbpf_reallocarray(res->addrs, res->alloc, sizeof(__u32));
> > +               if (!p)
> > +                       return -ENOMEM;
> > +               res->addrs = p;
> > +       }
> 
> please use libbpf_ensure_mem() instead

ok

> 
> 
> > +       res->addrs[res->cnt++] = sym_addr;
> > +       return 0;
> > +}
> > +
> > +static struct bpf_link *
> > +attach_fprobe_opts(const struct bpf_program *prog,
> > +                  const char *func_name,
> 
> func_glob or func_pattern?

ok

> 
> > +                  const struct bpf_kprobe_opts *kopts)
> > +{
> > +       DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts);
> > +       struct fprobe_resolve res = {
> > +               .name = func_name,
> > +       };
> > +       struct bpf_link *link = NULL;
> > +       char errmsg[STRERR_BUFSIZE];
> > +       int err, link_fd, prog_fd;
> > +       bool retprobe;
> > +
> > +       err = libbpf__kallsyms_parse(&res, resolve_fprobe_cb);
> > +       if (err)
> > +               goto error;
> > +       if (!res.cnt) {
> > +               err = -ENOENT;
> > +               goto error;
> > +       }
> > +
> > +       retprobe = OPTS_GET(kopts, retprobe, false);
> > +
> > +       opts.fprobe.addrs = (__u64) res.addrs;
> 
> ptr_to_u64()

ok

> 
> > +       opts.fprobe.cnt = res.cnt;
> > +       opts.flags = retprobe ? BPF_F_FPROBE_RETURN : 0;
> > +
> > +       link = calloc(1, sizeof(*link));
> > +       if (!link) {
> > +               err = -ENOMEM;
> > +               goto error;
> > +       }
> > +       link->detach = &bpf_link__detach_fd;
> > +
> > +       prog_fd = bpf_program__fd(prog);
> > +       link_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_FPROBE, &opts);
> > +       if (link_fd < 0) {
> > +               err = -errno;
> > +               pr_warn("prog '%s': failed to attach to %s: %s\n",
> > +                       prog->name, res.name,
> > +                       libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > +               goto error;
> > +       }
> > +       link->fd = link_fd;
> > +       free(res.addrs);
> > +       return link;
> > +
> > +error:
> > +       free(link);
> > +       free(res.addrs);
> > +       return libbpf_err_ptr(err);
> > +}
> > +
> >  struct bpf_link *
> >  bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
> >                                 const char *func_name,
> > @@ -10047,6 +10166,9 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
> >         if (!OPTS_VALID(opts, bpf_kprobe_opts))
> >                 return libbpf_err_ptr(-EINVAL);
> >
> > +       if (prog->expected_attach_type == BPF_TRACE_FPROBE)
> > +               return attach_fprobe_opts(prog, func_name, opts);
> > +
> >         retprobe = OPTS_GET(opts, retprobe, false);
> >         offset = OPTS_GET(opts, offset, 0);
> >         pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
> > @@ -10112,6 +10234,14 @@ struct bpf_link *bpf_program__attach_kprobe(const struct bpf_program *prog,
> >         return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
> >  }
> >
> > +static int init_kprobe(struct bpf_program *prog, long cookie)
> > +{
> > +       /* If we have wildcard, switch to fprobe link. */
> > +       if (strchr(prog->sec_name, '*'))
> 
> ugh... :( maybe let's have a separate SEC("kprobe.multi/<glob>") and
> same for kretprobe?

I agree new SEC type is more clear ;-) ok

thanks,
jirka