From 100089d560d0c996b31dd21ab2d1311fd8fba041 Mon Sep 17 00:00:00 2001 From: Hoyeon Lee Date: Wed, 1 Apr 2026 23:29:30 +0900 Subject: [PATCH] libbpf: Clarify raw-address single kprobe attach behavior 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 Signed-off-by: Andrii Nakryiko Acked-by: Jiri Olsa Link: https://lore.kernel.org/bpf/20260401143116.185049-3-hoyeon.lee@suse.com --- src/libbpf.c | 14 ++++++++------ src/libbpf.h | 27 ++++++++++++++++++++++++++- 2 files changed, 34 insertions(+), 7 deletions(-) diff --git a/src/libbpf.c b/src/libbpf.c index d9c678e..42bdba4 100644 --- a/src/libbpf.c +++ b/src/libbpf.c @@ -11843,6 +11843,8 @@ 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, @@ -11863,20 +11865,20 @@ 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/src/libbpf.h b/src/libbpf.h index 0be3485..bba4e84 100644 --- a/src/libbpf.h +++ b/src/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,