Re: [PATCH bpf-next v6 2/3] libbpf: clarify raw-address single kprobe attach behavior

[Jiri Olsa]

On Wed, Apr 01, 2026 at 04:05:03PM +0900, Hoyeon Lee wrote:
> bpf_program__attach_kprobe_opts() documents single-kprobe attach
> through func_name, with an optional offset. For the PMU-based path,
> func_name = NULL with an absolute address in offset already works as
> well, but that is not described in the API.
> 
> This commit clarifies this existing non-legacy behavior. For PMU-based
> attach, callers can use func_name = NULL with an absolute address in
> offset as the raw-address form. For legacy tracefs/debugfs kprobes,
> reject this form explicitly.
> 
> Signed-off-by: Hoyeon Lee <hoyeon.lee@xxxxxxxx>

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

jirka


> ---
>  tools/lib/bpf/libbpf.c | 14 ++++++++------
>  tools/lib/bpf/libbpf.h | 27 ++++++++++++++++++++++++++-
>  2 files changed, 34 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 536c19c14d21..ebb965230bb4 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11816,6 +11816,8 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
>  	default:
>  		return libbpf_err_ptr(-EINVAL);
>  	}
> +	if (!func_name && legacy)
> +		return libbpf_err_ptr(-EOPNOTSUPP);
>  
>  	if (!legacy) {
>  		pfd = perf_event_open_probe(false /* uprobe */, retprobe,
> @@ -11836,20 +11838,20 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
>  	}
>  	if (pfd < 0) {
>  		err = pfd;
> -		pr_warn("prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n",
> +		pr_warn("prog '%s': failed to create %s '%s%s0x%zx' perf event: %s\n",
>  			prog->name, retprobe ? "kretprobe" : "kprobe",
> -			func_name, offset,
> -			errstr(err));
> +			func_name ?: "", func_name ? "+" : "",
> +			offset, errstr(err));
>  		goto err_out;
>  	}
>  	link = bpf_program__attach_perf_event_opts(prog, pfd, &pe_opts);
>  	err = libbpf_get_error(link);
>  	if (err) {
>  		close(pfd);
> -		pr_warn("prog '%s': failed to attach to %s '%s+0x%zx': %s\n",
> +		pr_warn("prog '%s': failed to attach to %s '%s%s0x%zx': %s\n",
>  			prog->name, retprobe ? "kretprobe" : "kprobe",
> -			func_name, offset,
> -			errstr(err));
> +			func_name ?: "", func_name ? "+" : "",
> +			offset, errstr(err));
>  		goto err_clean_legacy;
>  	}
>  	if (legacy) {
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 0be34852350f..bba4e8464396 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -557,7 +557,7 @@ struct bpf_kprobe_opts {
>  	size_t sz;
>  	/* custom user-provided value fetchable through bpf_get_attach_cookie() */
>  	__u64 bpf_cookie;
> -	/* function's offset to install kprobe to */
> +	/* function offset, or raw address if func_name == NULL */
>  	size_t offset;
>  	/* kprobe is return probe */
>  	bool retprobe;
> @@ -565,11 +565,36 @@ struct bpf_kprobe_opts {
>  	enum probe_attach_mode attach_mode;
>  	size_t :0;
>  };
> +
>  #define bpf_kprobe_opts__last_field attach_mode
>  
> +/**
> + * @brief **bpf_program__attach_kprobe()** attaches a BPF program to a
> + * kernel function entry or return.
> + *
> + * @param prog BPF program to attach
> + * @param retprobe Attach to function return
> + * @param func_name Name of the kernel function to attach to
> + * @return Reference to the newly created BPF link; or NULL is returned on
> + * error, error code is stored in errno
> + */
>  LIBBPF_API struct bpf_link *
>  bpf_program__attach_kprobe(const struct bpf_program *prog, bool retprobe,
>  			   const char *func_name);
> +
> +/**
> + * @brief **bpf_program__attach_kprobe_opts()** is just like
> + * bpf_program__attach_kprobe() except with an options struct
> + * for various configurations.
> + *
> + * @param prog BPF program to attach
> + * @param func_name Name of the kernel function to attach to. If NULL,
> + * opts->offset is treated as a raw kernel address. Raw-address attach
> + * is supported with PROBE_ATTACH_MODE_PERF and PROBE_ATTACH_MODE_LINK.
> + * @param opts Options for altering program attachment
> + * @return Reference to the newly created BPF link; or NULL is returned on
> + * error, error code is stored in errno
> + */
>  LIBBPF_API struct bpf_link *
>  bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
>                                  const char *func_name,
> -- 
> 2.52.0
>