On Fri, Apr 8, 2022 at 1:34 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> In a lot of cases the target of kprobe/kretprobe, tracepoint, raw
> tracepoint, etc BPF program might not be known at the compilation time
> and will be discovered at runtime. This was always a supported case by
> libbpf, with APIs like bpf_program__attach_{kprobe,tracepoint,etc}()
> accepting full target definition, regardless of what was defined in
> SEC() definition in BPF source code.
>
> Unfortunately, up till now libbpf still enforced users to specify at
> least something for the fake target, e.g., SEC("kprobe/whatever"), which
> is cumbersome and somewhat misleading.
>
> This patch allows target-less SEC() definitions for basic tracing BPF
> program types:
> - kprobe/kretprobe;
> - multi-kprobe/multi-kretprobe;
> - tracepoints;
> - raw tracepoints.
>
> Such target-less SEC() definitions are meant to specify declaratively
> proper BPF program type only. Attachment of them will have to be handled
> programmatically using correct APIs. As such, skeleton's auto-attachment
> of such BPF programs is skipped and generic bpf_program__attach() will
> fail, if attempted, due to the lack of enough target information.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 69 +++++++++++++++++++++++++++++++-----------
> 1 file changed, 51 insertions(+), 18 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 9deb1fc67f19..81911a1e1f3e 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8668,22 +8668,22 @@ static const struct bpf_sec_def section_defs[] = {
> SEC_DEF("socket", SOCKET_FILTER, 0, SEC_NONE | SEC_SLOPPY_PFX),
> SEC_DEF("sk_reuseport/migrate", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT_OR_MIGRATE, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
> SEC_DEF("sk_reuseport", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT, SEC_ATTACHABLE | SEC_SLOPPY_PFX),
> - SEC_DEF("kprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
> + SEC_DEF("kprobe+", KPROBE, 0, SEC_NONE, attach_kprobe),
> SEC_DEF("uprobe+", KPROBE, 0, SEC_NONE, attach_uprobe),
> - SEC_DEF("kretprobe/", KPROBE, 0, SEC_NONE, attach_kprobe),
> + SEC_DEF("kretprobe+", KPROBE, 0, SEC_NONE, attach_kprobe),
> SEC_DEF("uretprobe+", KPROBE, 0, SEC_NONE, attach_uprobe),
> - SEC_DEF("kprobe.multi/", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
> - SEC_DEF("kretprobe.multi/", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
> + SEC_DEF("kprobe.multi+", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
> + SEC_DEF("kretprobe.multi+", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
> SEC_DEF("usdt+", KPROBE, 0, SEC_NONE, attach_usdt),
> SEC_DEF("tc", SCHED_CLS, 0, SEC_NONE),
> SEC_DEF("classifier", SCHED_CLS, 0, SEC_NONE | SEC_SLOPPY_PFX | SEC_DEPRECATED),
> SEC_DEF("action", SCHED_ACT, 0, SEC_NONE | SEC_SLOPPY_PFX),
> - SEC_DEF("tracepoint/", TRACEPOINT, 0, SEC_NONE, attach_tp),
> - SEC_DEF("tp/", TRACEPOINT, 0, SEC_NONE, attach_tp),
> - SEC_DEF("raw_tracepoint/", RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
> - SEC_DEF("raw_tp/", RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
> - SEC_DEF("raw_tracepoint.w/", RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
> - SEC_DEF("raw_tp.w/", RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
> + SEC_DEF("tracepoint+", TRACEPOINT, 0, SEC_NONE, attach_tp),
> + SEC_DEF("tp+", TRACEPOINT, 0, SEC_NONE, attach_tp),
> + SEC_DEF("raw_tracepoint+", RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
> + SEC_DEF("raw_tp+", RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
> + SEC_DEF("raw_tracepoint.w+", RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
> + SEC_DEF("raw_tp.w+", RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
> SEC_DEF("tp_btf/", TRACING, BPF_TRACE_RAW_TP, SEC_ATTACH_BTF, attach_trace),
> SEC_DEF("fentry/", TRACING, BPF_TRACE_FENTRY, SEC_ATTACH_BTF, attach_trace),
> SEC_DEF("fmod_ret/", TRACING, BPF_MODIFY_RETURN, SEC_ATTACH_BTF, attach_trace),
> @@ -10411,6 +10411,12 @@ static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf
> char *func;
> int n;
>
> + *link = NULL;
> +
> + /* no auto-attach for SEC("kprobe") and SEC("kretprobe") */
> + if (strcmp(prog->sec_name, "kprobe") == 0 || strcmp(prog->sec_name, "kretprobe") == 0)
> + return 0;
> +
> opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe/");
> if (opts.retprobe)
> func_name = prog->sec_name + sizeof("kretprobe/") - 1;
> @@ -10441,6 +10447,13 @@ static int attach_kprobe_multi(const struct bpf_program *prog, long cookie, stru
> char *pattern;
> int n;
>
> + *link = NULL;
> +
> + /* no auto-attach for SEC("kprobe.multi") and SEC("kretprobe.multi") */
> + if (strcmp(prog->sec_name, "kprobe.multi") == 0 ||
> + strcmp(prog->sec_name, "kretprobe.multi") == 0)
> + return 0;
> +
> opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe.multi/");
> if (opts.retprobe)
> spec = prog->sec_name + sizeof("kretprobe.multi/") - 1;
> @@ -11145,6 +11158,12 @@ static int attach_tp(const struct bpf_program *prog, long cookie, struct bpf_lin
> if (!sec_name)
> return -ENOMEM;
>
> + *link = NULL;
> +
> + /* no auto-attach for SEC("tp") or SEC("tracepoint") */
> + if (strcmp(prog->sec_name, "tp") == 0 || strcmp(prog->sec_name, "tracepoint") == 0)
> + return 0;
> +
> /* extract "tp/<category>/<name>" or "tracepoint/<category>/<name>" */
> if (str_has_pfx(prog->sec_name, "tp/"))
> tp_cat = sec_name + sizeof("tp/") - 1;
> @@ -11196,20 +11215,34 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(const struct bpf_program *pr
> static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link)
> {
> static const char *const prefixes[] = {
> - "raw_tp/",
> - "raw_tracepoint/",
> - "raw_tp.w/",
> - "raw_tracepoint.w/",
> + "raw_tp",
> + "raw_tracepoint",
> + "raw_tp.w",
> + "raw_tracepoint.w",
> };
> size_t i;
> const char *tp_name = NULL;
>
> + *link = NULL;
> +
> for (i = 0; i < ARRAY_SIZE(prefixes); i++) {
> - if (str_has_pfx(prog->sec_name, prefixes[i])) {
> - tp_name = prog->sec_name + strlen(prefixes[i]);
> - break;
> - }
> + size_t pfx_len;
> +
> + if (!str_has_pfx(prog->sec_name, prefixes[i]))
> + continue;
> +
> + pfx_len = strlen(prefixes[i]);
> + /* no auto-attach case of, e.g., SEC("raw_tp") */
> + if (prog->sec_name[pfx_len] == '\0')
> + return 0;
> +
> + if (prog->sec_name[pfx_len] != '/')
> + continue;
Maybe introduce a sec_has_pfx() function with tri-state return value:
1 for match with tp_name, 0, for match without tp_name, -1 for no match.
> +
> + tp_name = prog->sec_name + pfx_len + 1;
> + break;
> }
> +
> if (!tp_name) {
> pr_warn("prog '%s': invalid section name '%s'\n",
> prog->name, prog->sec_name);
> --
> 2.30.2
>
