Re: [PATCHv3 4/7] libbpf: Add support for uprobe multi session attach

Andrii Nakryiko
2024-09-09T23:44:57Z

On Mon, Sep 9, 2024 at 12:46 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding support to attach program in uprobe session mode
> with bpf_program__attach_uprobe_multi function.
>
> Adding session bool to bpf_uprobe_multi_opts struct that allows
> to load and attach the bpf program via uprobe session.
> the attachment to create uprobe multi session.
>
> Also adding new program loader section that allows:
> SEC("uprobe.session/bpf_fentry_test*")
>
> and loads/attaches uprobe program as uprobe session.
>
> Adding sleepable hook (uprobe.session.s) as well.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> tools/lib/bpf/bpf.c | 1 +
> tools/lib/bpf/libbpf.c | 50 ++++++++++++++++++++++++++++++++++++++++--
> tools/lib/bpf/libbpf.h | 4 +++-
> 3 files changed, 52 insertions(+), 3 deletions(-)
>

[...]

> +static int attach_uprobe_session(const struct bpf_program *prog, long cookie, struct bpf_link **link)
> +{
> + LIBBPF_OPTS(bpf_uprobe_multi_opts, opts, .session = true);
> + char *binary_path = NULL, *func_name = NULL;
> + int n, ret = -EINVAL;
> + const char *spec;
> +
> + *link = NULL;
> +
> + spec = prog->sec_name + sizeof("uprobe.session/") - 1;
> + if (cookie & SEC_SLEEPABLE)
> + spec += 2; /* extra '.s' */
> + n = sscanf(spec, "%m[^:]:%m[^\n]", &binary_path, &func_name);
> +
> + switch (n) {
> + case 1:
> + /* but auto-attach is impossible. */
> + ret = 0;
> + break;
> + case 2:
> + *link = bpf_program__attach_uprobe_multi(prog, -1, binary_path, func_name, &opts);
> + ret = *link ? 0 : -errno;
> + break;
> + default:
> + pr_warn("prog '%s': invalid format of section definition '%s'\n", prog->name,
> + prog->sec_name);
> + break;
> + }
> + free(binary_path);
> + free(func_name);
> + return ret;
> +}

why adding this whole attach_uprobe_session if attach_uprobe_multi()
is almost exactly what you need. We just need to teach
attach_uprobe_multi to recognize uprobe.session prefix with strncmp(),
no? The rest of the logic is exactly the same.

BTW, maybe you can fix attach_uprobe_multi() while at it:

opts.retprobe = strcmp(probe_type, "uretprobe.multi") == 0;

that should be strncmp() to accommodate uretprobe.multi.s, no?
Original author (wink-wink) didn't account for that ".s", it seems...

(actually please send a small fix to bpf-next separately, so we can
apply it sooner)

> +
> static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
> const char *binary_path, uint64_t offset)
> {
> @@ -11933,10 +11969,12 @@ bpf_program__attach_uprobe_multi(const struct bpf_program *prog,
> const unsigned long *ref_ctr_offsets = NULL, *offsets = NULL;
> LIBBPF_OPTS(bpf_link_create_opts, lopts);
> unsigned long *resolved_offsets = NULL;
> + enum bpf_attach_type attach_type;
> int err = 0, link_fd, prog_fd;
> struct bpf_link *link = NULL;
> char errmsg[STRERR_BUFSIZE];
> char full_path[PATH_MAX];
> + bool retprobe, session;
> const __u64 *cookies;
> const char **syms;
> size_t cnt; …