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Date: Mon, 27 Feb 2023 13:47:52 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: menglong8.dong@...il.com
Cc: alan.maguire@...cle.com, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
benbjiang@...cent.com, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, Menglong Dong <imagedong@...cent.com>
Subject: Re: [PATCH bpf-next v3 1/3] libbpf: add support to set kprobe/uprobe
attach mode
On Mon, Feb 20, 2023 at 6:54 PM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> By default, libbpf will attach the kprobe/uprobe eBPF program in the
> latest mode that supported by kernel. In this patch, we add the support
> to let users manually attach kprobe/uprobe in legacy or perf mode.
>
> There are 3 mode that supported by the kernel to attach kprobe/uprobe:
>
> LEGACY: create perf event in legacy way and don't use bpf_link
> PERF: create perf event with perf_event_open() and don't use bpf_link
> LINK: create perf event with perf_event_open() and use bpf_link
>
> Users now can manually choose the mode with
> bpf_program__attach_uprobe_opts()/bpf_program__attach_kprobe_opts().
>
> Link: https://lore.kernel.org/bpf/20230113093427.1666466-1-imagedong@tencent.com/
> Reviewed-by: Biao Jiang <benbjiang@...cent.com>
> Signed-off-by: Menglong Dong <imagedong@...cent.com>
> Reviewed-by: Alan Maguire <alan.maguire@...cle.com>
> ---
> v2:
> - rename no_link to force_ioctl_attach
> - rename probe_mode to probe_attach_mode
> - add more doc for probe_attach_mode
> - return -ENOTSUP when necessray in bpf_program__attach_uprobe_opts and
> bpf_program__attach_kprobe_opts
> ---
> tools/lib/bpf/libbpf.c | 42 +++++++++++++++++++++++++++++++++++++++++-
> tools/lib/bpf/libbpf.h | 31 ++++++++++++++++++++++++++++---
> 2 files changed, 69 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 05c4db355f28..d07a0d7b9edd 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -9747,7 +9747,7 @@ struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *p
> link->link.dealloc = &bpf_link_perf_dealloc;
> link->perf_event_fd = pfd;
>
> - if (kernel_supports(prog->obj, FEAT_PERF_LINK)) {
> + if (kernel_supports(prog->obj, FEAT_PERF_LINK) && !opts->force_ioctl_attach) {
can't access ->force_ioctl_attach directly, please use OPTS_GET()
macro; it handles possibility of old user app passing smaller and
older version of opts struct
> DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts,
> .perf_event.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0));
>
> @@ -10106,6 +10106,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
> const struct bpf_kprobe_opts *opts)
> {
> DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
> + enum probe_attach_mode attach_mode;
> char errmsg[STRERR_BUFSIZE];
> char *legacy_probe = NULL;
> struct bpf_link *link;
> @@ -10116,11 +10117,30 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
> if (!OPTS_VALID(opts, bpf_kprobe_opts))
> return libbpf_err_ptr(-EINVAL);
>
> + attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
> retprobe = OPTS_GET(opts, retprobe, false);
> offset = OPTS_GET(opts, offset, 0);
> pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
>
> legacy = determine_kprobe_perf_type() < 0;
> + switch (attach_mode) {
> + case PROBE_ATTACH_MODE_LEGACY:
> + legacy = true;
> + pe_opts.force_ioctl_attach = true;
> + break;
> + case PROBE_ATTACH_MODE_PERF:
> + if (legacy)
> + return libbpf_err_ptr(-ENOTSUP);
> + pe_opts.force_ioctl_attach = true;
> + break;
> + case PROBE_ATTACH_MODE_LINK:
> + if (!kernel_supports(prog->obj, FEAT_PERF_LINK))
just to be on the safe side, let's also check that we are not in
legacy mode here?
> + return libbpf_err_ptr(-ENOTSUP);
> + break;
> + default:
let's add case PROBE_ATTACH_MODE_DEFAULT: break; explicitly, but for
all other unknown values error out
> + break;
> + }
> +
> if (!legacy) {
> pfd = perf_event_open_probe(false /* uprobe */, retprobe,
> func_name, offset,
> @@ -10774,6 +10794,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
> {
> DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
> char errmsg[STRERR_BUFSIZE], *legacy_probe = NULL;
> + enum probe_attach_mode attach_mode;
> char full_binary_path[PATH_MAX];
> struct bpf_link *link;
> size_t ref_ctr_off;
> @@ -10784,6 +10805,7 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
> if (!OPTS_VALID(opts, bpf_uprobe_opts))
> return libbpf_err_ptr(-EINVAL);
>
> + attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
> retprobe = OPTS_GET(opts, retprobe, false);
> ref_ctr_off = OPTS_GET(opts, ref_ctr_offset, 0);
> pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
> @@ -10812,6 +10834,24 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
> }
>
> legacy = determine_uprobe_perf_type() < 0;
> + switch (attach_mode) {
> + case PROBE_ATTACH_MODE_LEGACY:
> + legacy = true;
> + pe_opts.force_ioctl_attach = true;
> + break;
> + case PROBE_ATTACH_MODE_PERF:
> + if (legacy)
> + return libbpf_err_ptr(-ENOTSUP);
> + pe_opts.force_ioctl_attach = true;
> + break;
> + case PROBE_ATTACH_MODE_LINK:
> + if (!kernel_supports(prog->obj, FEAT_PERF_LINK))
> + return libbpf_err_ptr(-ENOTSUP);
> + break;
> + default:
> + break;
> + }
all the same points as above for kprobe_opts version
> +
> if (!legacy) {
> pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,
> func_offset, pid, ref_ctr_off);
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 2efd80f6f7b9..ef8f68da42f9 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -451,8 +451,11 @@ struct bpf_perf_event_opts {
> size_t sz;
> /* custom user-provided value fetchable through bpf_get_attach_cookie() */
> __u64 bpf_cookie;
> + /* don't use bpf_link when attach eBPF program */
> + bool force_ioctl_attach;
> + size_t :0;
> };
> -#define bpf_perf_event_opts__last_field bpf_cookie
> +#define bpf_perf_event_opts__last_field force_ioctl_attach
>
> LIBBPF_API struct bpf_link *
> bpf_program__attach_perf_event(const struct bpf_program *prog, int pfd);
> @@ -461,6 +464,24 @@ LIBBPF_API struct bpf_link *
> bpf_program__attach_perf_event_opts(const struct bpf_program *prog, int pfd,
> const struct bpf_perf_event_opts *opts);
>
> +
> +/**
> + * enum probe_attach_mode - the mode to attach kprobe/uprobe
> + *
> + * force libbpf to attach kprobe/uprobe in specific mode, -ENOTSUP will
> + * be returned if it is not supported by the kernel.
> + */
> +enum probe_attach_mode {
> + /* attach probe in latest supported mode by kernel */
> + PROBE_ATTACH_MODE_DEFAULT = 0,
> + /* attach probe in legacy mode */
"in legacy mode, using debugfs/tracefs" ?
> + PROBE_ATTACH_MODE_LEGACY,
> + /* create perf event with perf_event_open() syscall */
> + PROBE_ATTACH_MODE_PERF,
> + /* attach probe with bpf_link */
nit: BPF link (it's a concept, not a struct name)
> + PROBE_ATTACH_MODE_LINK,
> +};
> +
> struct bpf_kprobe_opts {
> /* size of this struct, for forward/backward compatiblity */
> size_t sz;
> @@ -470,9 +491,11 @@ struct bpf_kprobe_opts {
> size_t offset;
> /* kprobe is return probe */
> bool retprobe;
> + /* kprobe attach mode */
> + enum probe_attach_mode attach_mode;
> size_t :0;
> };
> -#define bpf_kprobe_opts__last_field retprobe
> +#define bpf_kprobe_opts__last_field attach_mode
>
> LIBBPF_API struct bpf_link *
> bpf_program__attach_kprobe(const struct bpf_program *prog, bool retprobe,
> @@ -570,9 +593,11 @@ struct bpf_uprobe_opts {
> * binary_path.
> */
> const char *func_name;
> + /* uprobe attach mode */
> + enum probe_attach_mode attach_mode;
> size_t :0;
> };
> -#define bpf_uprobe_opts__last_field func_name
> +#define bpf_uprobe_opts__last_field attach_mode
>
> /**
> * @brief **bpf_program__attach_uprobe()** attaches a BPF program
> --
> 2.39.0
>
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