On Wed, Dec 18, 2024 at 5:53 PM Yonghong Song <yonghong.song@xxxxxxxxx> wrote:
>
> Jordan reported an issue in Meta production environment where func
> try_to_wake_up() is renamed to try_to_wake_up.llvm.<hash>() by clang
> compiler at lto mode. The original 'kprobe/try_to_wake_up' does not
> work any more since try_to_wake_up() does not match the actual func
> name in /proc/kallsyms.
>
> There are a couple of ways to resolve this issue. For example, in
> attach_kprobe(), we could do lookup in /proc/kallsyms so try_to_wake_up()
> can be replaced by try_to_wake_up.llvm.<hach>(). Or we can force users
> to use bpf_program__attach_kprobe() where they need to lookup
> /proc/kallsyms to find out try_to_wake_up.llvm.<hach>(). But these two
> approaches requires extra work by either libbpf or user.
>
> Luckily, suggested by Andrii, multi kprobe already supports wildcard ('*')
> for symbol matching. In the above example, 'try_to_wake_up*' can match
> to try_to_wake_up() or try_to_wake_up.llvm.<hash>() and this allows
> bpf prog works for different kernels as some kernels may have
> try_to_wake_up() and some others may have try_to_wake_up.llvm.<hash>().
>
> The original intention is to kprobe try_to_wake_up() only, so an optional
> field unique_match is added to struct bpf_kprobe_multi_opts. If the
> field is set to true, the number of matched functions must be one.
> Otherwise, the attachment will fail. In the above case, multi kprobe
> with 'try_to_wake_up*' and unique_match preserves user functionality.
>
> Reported-by: Jordan Rome <linux@xxxxxxxxxxxxxx>
> Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 10 +++++++++-
> tools/lib/bpf/libbpf.h | 4 +++-
> 2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 66173ddb5a2d..649c6e92972a 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11522,7 +11522,7 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
> struct bpf_link *link = NULL;
> const unsigned long *addrs;
> int err, link_fd, prog_fd;
> - bool retprobe, session;
> + bool retprobe, session, unique_match;
> const __u64 *cookies;
> const char **syms;
> size_t cnt;
> @@ -11558,6 +11558,14 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
> err = libbpf_available_kallsyms_parse(&res);
> if (err)
> goto error;
> +
> + unique_match = OPTS_GET(opts, unique_match, false);
> + if (unique_match && res.cnt != 1) {
> + pr_warn("prog '%s': failed to find unique match: cnt %lu\n",
> + prog->name, res.cnt);
nit: "failed to find a unique match. Num matches: %lu\n"
or "Failed to find a unique match for %s'. Num matches: %lu\n"
> + return libbpf_err_ptr(-EINVAL);
> + }
> +
> addrs = res.addrs;
> cnt = res.cnt;
> }
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index d45807103565..3020ee45303a 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -552,10 +552,12 @@ struct bpf_kprobe_multi_opts {
> bool retprobe;
> /* create session kprobes */
> bool session;
> + /* enforce unique match */
> + bool unique_match;
> size_t :0;
> };
>
> -#define bpf_kprobe_multi_opts__last_field session
> +#define bpf_kprobe_multi_opts__last_field unique_match
>
> LIBBPF_API struct bpf_link *
> bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
> --
> 2.43.5
>
Ack. Thanks for the quick work, Yonghong!
