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[37.188.160.213]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48730628efasm277656905e9.5.2026.03.30.03.08.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 30 Mar 2026 03:08:11 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 30 Mar 2026 12:08:08 +0200 To: Hoyeon Lee Cc: bpf@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Shuah Khan , Feng Yang , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next v2 1/2] libbpf: allow address-based single kprobe attach Message-ID: References: <20260329124429.689912-1-hoyeon.lee@suse.com> <20260329124429.689912-2-hoyeon.lee@suse.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260329124429.689912-2-hoyeon.lee@suse.com> On Sun, Mar 29, 2026 at 09:43:38PM +0900, Hoyeon Lee wrote: > bpf_program__attach_kprobe_opts() currently attaches a single kprobe only > by func_name, with an optional offset. This covers only the symbol- > based form, not the raw-address form that the kernel already supports > for both kprobe PMU events and legacy tracefs/debugfs kprobes. Callers > that already have a target IP still have to drop down to > perf_event_open() or direct tracefs writes. > > libbpf already exposes address-based attach for kprobe_multi through > bpf_kprobe_multi_opts.addrs. This commit adds bpf_kprobe_opts.addr so > that single kprobes can be attached either by func_name + offset or by > raw address. curious, is this change just for the api to be complete or you do have a usecase where you can't use kprobe_multi and need to attach kprobe by address? SNIP > static void gen_probe_legacy_event_name(char *buf, size_t buf_sz, > - const char *name, size_t offset) > + const char *name, > + uint64_t offset_or_addr) > { > static int index = 0; > int i; > > - snprintf(buf, buf_sz, "libbpf_%u_%d_%s_0x%zx", getpid(), > - __sync_fetch_and_add(&index, 1), name, offset); > + snprintf(buf, buf_sz, "libbpf_%u_%d_%s_0x%" PRIx64, getpid(), > + __sync_fetch_and_add(&index, 1), name ?: "addr", > + offset_or_addr); > > /* sanitize name in the probe name */ > for (i = 0; buf[i]; i++) { > @@ -11648,13 +11651,28 @@ static void gen_probe_legacy_event_name(char *buf, size_t buf_sz, > } > } > > +static void gen_kprobe_target(char *buf, size_t buf_sz, const char *name, > + uint64_t offset_or_addr) > +{ > + if (name) > + snprintf(buf, buf_sz, "%s+0x%" PRIx64, name, offset_or_addr); > + else > + snprintf(buf, buf_sz, "0x%" PRIx64, offset_or_addr); > +} > + > static int add_kprobe_event_legacy(const char *probe_name, bool retprobe, > - const char *kfunc_name, size_t offset) > + const char *kfunc_name, > + uint64_t offset_or_addr) > { > - return append_to_file(tracefs_kprobe_events(), "%c:%s/%s %s+0x%zx", > + char probe_target[128]; > + > + gen_kprobe_target(probe_target, sizeof(probe_target), kfunc_name, > + offset_or_addr); > + it seems like it'd be easier to get probe_target (via gen_kprobe_target) in bpf_program__attach_kprobe_opts and pass it down instead of generating it over and over again > + return append_to_file(tracefs_kprobe_events(), "%c:%s/%s %s", > retprobe ? 'r' : 'p', > retprobe ? "kretprobes" : "kprobes", > - probe_name, kfunc_name, offset); > + probe_name, probe_target); > } > > static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe) > @@ -11674,25 +11692,29 @@ static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retpro > } > > static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe, > - const char *kfunc_name, size_t offset, int pid) > + const char *kfunc_name, > + uint64_t offset_or_addr, int pid) > { > const size_t attr_sz = sizeof(struct perf_event_attr); > struct perf_event_attr attr; > int type, pfd, err; > + char probe_target[128]; we need bigger buffer as explained by sashiko [1] [1] https://sashiko.dev/#/patchset/20260329124429.689912-1-hoyeon.lee%40suse.com jirka > > - err = add_kprobe_event_legacy(probe_name, retprobe, kfunc_name, offset); > + gen_kprobe_target(probe_target, sizeof(probe_target), kfunc_name, > + offset_or_addr); > + > + err = add_kprobe_event_legacy(probe_name, retprobe, kfunc_name, > + offset_or_addr); > if (err < 0) { > - pr_warn("failed to add legacy kprobe event for '%s+0x%zx': %s\n", > - kfunc_name, offset, > - errstr(err)); > + pr_warn("failed to add legacy kprobe event for '%s': %s\n", > + probe_target, errstr(err)); > return err; > } > type = determine_kprobe_perf_type_legacy(probe_name, retprobe); > if (type < 0) { > err = type; > - pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n", > - kfunc_name, offset, > - errstr(err)); > + pr_warn("failed to determine legacy kprobe event id for '%s': %s\n", > + probe_target, errstr(err)); > goto err_clean_legacy; > } > SNIP