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[37.188.182.96]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab6760ab280sm11191266b.104.2025.01.23.12.12.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jan 2025 12:12:03 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 23 Jan 2025 21:11:58 +0100 To: Jiri Olsa Cc: Tao Chen , ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, haoluo@google.com, qmo@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH bpf-next 1/2] libbpf: Add libbpf_probe_bpf_kfunc API Message-ID: References: <20250122170620.218533-1-chen.dylane@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@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: On Thu, Jan 23, 2025 at 09:07:11PM +0100, Jiri Olsa wrote: > On Thu, Jan 23, 2025 at 01:06:19AM +0800, Tao Chen wrote: > > Similarly to libbpf_probe_bpf_helper, the libbpf_probe_bpf_kfunc > > used to test the availability of the different eBPF kfuncs on the > > current system. > > hi, > there's "bpf_kfunc" DECL_TAG for each kfunc in BTF data, > I think that should do the same job? please check [1] and > related commits for details nah there's v2 with support for modules.. makes sense then, will check sorry for noise ;-) jirka > > jirka > > > [1] 770abbb5a25a bpftool: Support dumping kfunc prototypes from BTF > > > > > Signed-off-by: Tao Chen > > --- > > tools/lib/bpf/libbpf.h | 16 +++++++++++++++- > > tools/lib/bpf/libbpf.map | 1 + > > tools/lib/bpf/libbpf_probes.c | 36 +++++++++++++++++++++++++++++++++++ > > 3 files changed, 52 insertions(+), 1 deletion(-) > > > > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > > index 3020ee45303a..3b6d33578a16 100644 > > --- a/tools/lib/bpf/libbpf.h > > +++ b/tools/lib/bpf/libbpf.h > > @@ -1680,7 +1680,21 @@ LIBBPF_API int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void > > */ > > LIBBPF_API int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, > > enum bpf_func_id helper_id, const void *opts); > > - > > +/** > > + * @brief **libbpf_probe_bpf_kfunc()** detects if host kernel supports the > > + * use of a given BPF kfunc from specified BPF program type. > > + * @param prog_type BPF program type used to check the support of BPF kfunc > > + * @param kfunc_id The btf ID of BPF kfunc to check support for > > + * @param opts reserved for future extensibility, should be NULL > > + * @return 1, if given combination of program type and kfunc is supported; 0, > > + * if the combination is not supported; negative error code if feature > > + * detection for provided input arguments failed or can't be performed > > + * > > + * Make sure the process has required set of CAP_* permissions (or runs as > > + * root) when performing feature checking. > > + */ > > +LIBBPF_API int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, > > + int kfunc_id, const void *opts); > > /** > > * @brief **libbpf_num_possible_cpus()** is a helper function to get the > > * number of possible CPUs that the host kernel supports and expects. > > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map > > index a8b2936a1646..e93fae101efd 100644 > > --- a/tools/lib/bpf/libbpf.map > > +++ b/tools/lib/bpf/libbpf.map > > @@ -436,4 +436,5 @@ LIBBPF_1.6.0 { > > bpf_linker__add_buf; > > bpf_linker__add_fd; > > bpf_linker__new_fd; > > + libbpf_probe_bpf_kfunc; > > } LIBBPF_1.5.0; > > diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c > > index 9dfbe7750f56..bc1cf2afbe87 100644 > > --- a/tools/lib/bpf/libbpf_probes.c > > +++ b/tools/lib/bpf/libbpf_probes.c > > @@ -413,6 +413,42 @@ int libbpf_probe_bpf_map_type(enum bpf_map_type map_type, const void *opts) > > return libbpf_err(ret); > > } > > > > +int libbpf_probe_bpf_kfunc(enum bpf_prog_type prog_type, int kfunc_id, > > + const void *opts) > > +{ > > + struct bpf_insn insns[] = { > > + BPF_EXIT_INSN(), > > + BPF_EXIT_INSN(), > > + }; > > + const size_t insn_cnt = ARRAY_SIZE(insns); > > + int err; > > + char buf[4096]; > > + > > + if (opts) > > + return libbpf_err(-EINVAL); > > + > > + insns[0].code = BPF_JMP | BPF_CALL; > > + insns[0].src_reg = BPF_PSEUDO_KFUNC_CALL; > > + insns[0].imm = kfunc_id; > > + > > + /* Now only support kfunc from vmlinux */ > > + insns[0].off = 0; > > + > > + buf[0] = '\0'; > > + err = probe_prog_load(prog_type, insns, insn_cnt, buf, sizeof(buf)); > > + if (err < 0) > > + return libbpf_err(err); > > + > > + /* If BPF verifier recognizes BPF kfunc but it's not supported for > > + * given BPF program type, it will emit "calling kernel function > > + * bpf_cpumask_create is not allowed" > > + */ > > + if (err == 0 && strstr(buf, "not allowed")) > > + return 0; > > + > > + return 1; /* assume supported */ > > +} > > + > > int libbpf_probe_bpf_helper(enum bpf_prog_type prog_type, enum bpf_func_id helper_id, > > const void *opts) > > { > > -- > > 2.43.0 > >