From patchwork Thu Aug 17 22:53:52 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Marchevsky X-Patchwork-Id: 13357063 X-Patchwork-Delegate: bpf@iogearbox.net Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9EF13F9D5 for ; Thu, 17 Aug 2023 22:54:38 +0000 (UTC) Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 800D52D65 for ; Thu, 17 Aug 2023 15:54:37 -0700 (PDT) Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 37HHmXRa028710 for ; Thu, 17 Aug 2023 15:54:37 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : content-type : content-transfer-encoding : mime-version; s=facebook; bh=RPyxSei1bagjIjDcYGKF2XBRHizQ4u+4q8zKmKNfEwc=; b=h5aw5Vcx+GQJUZpGlOl6IRLBhrZnIhBSbw7ykX8rgI4jSnWOVn4xTxEcEY3ktZfuL25m atOyGaHQZwQqCFii/S+La4dJB1bMUwjCvm0MJeSckIhtUYTbw66e2sRtdLE8GRYRZC83 QWSWXtksvuR2vk8UTXU/qROrLfhDjnqI+3Y= Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3shgk2q9yb-11 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Thu, 17 Aug 2023 15:54:37 -0700 Received: from twshared13387.02.ash9.facebook.com (2620:10d:c085:108::8) by mail.thefacebook.com (2620:10d:c085:11d::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Thu, 17 Aug 2023 15:54:07 -0700 Received: by devbig077.ldc1.facebook.com (Postfix, from userid 158236) id 1233122D020D7; Thu, 17 Aug 2023 15:53:54 -0700 (PDT) From: Dave Marchevsky To: CC: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Kernel Team , Dave Marchevsky Subject: [PATCH v3 bpf-next 1/2] libbpf: Support triple-underscore flavors for kfunc relocation Date: Thu, 17 Aug 2023 15:53:52 -0700 Message-ID: <20230817225353.2570845-1-davemarchevsky@fb.com> X-Mailer: git-send-email 2.34.1 X-FB-Internal: Safe X-Proofpoint-GUID: L7qtksgZJra4AVfSHF9kEN1UgfYLIgyr X-Proofpoint-ORIG-GUID: L7qtksgZJra4AVfSHF9kEN1UgfYLIgyr X-Proofpoint-UnRewURL: 0 URL was un-rewritten Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.267,Aquarius:18.0.957,Hydra:6.0.601,FMLib:17.11.176.26 definitions=2023-08-17_18,2023-08-17_02,2023-05-22_02 X-Spam-Status: No, score=-2.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_LOW,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE, SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net X-Patchwork-Delegate: bpf@iogearbox.net The function signature of kfuncs can change at any time due to their intentional lack of stability guarantees. As kfuncs become more widely used, BPF program writers will need facilities to support calling different versions of a kfunc from a single BPF object. Consider this simplified example based on a real scenario we ran into at Meta: /* initial kfunc signature */ int some_kfunc(void *ptr) /* Oops, we need to add some flag to modify behavior. No problem, change the kfunc. flags = 0 retains original behavior */ int some_kfunc(void *ptr, long flags) If the initial version of the kfunc is deployed on some portion of the fleet and the new version on the rest, a fleetwide service that uses some_kfunc will currently need to load different BPF programs depending on which some_kfunc is available. Luckily CO-RE provides a facility to solve a very similar problem, struct definition changes, by allowing program writers to declare my_struct___old and my_struct___new, with ___suffix being considered a 'flavor' of the non-suffixed name and being ignored by bpf_core_type_exists and similar calls. This patch extends the 'flavor' facility to the kfunc extern relocation process. BPF program writers can now declare extern int some_kfunc___old(void *ptr) extern int some_kfunc___new(void *ptr, int flags) then test which version of the kfunc exists with bpf_ksym_exists. Relocation and verifier's dead code elimination will work in concert as expected, allowing this pattern: if (bpf_ksym_exists(some_kfunc___old)) some_kfunc___old(ptr); else some_kfunc___new(ptr, 0); Changelog: v1 -> v2: https://lore.kernel.org/bpf/20230811201346.3240403-1-davemarchevsky@fb.com/ * No need to check obj->externs[i].essent_name before zfree (Jiri) * Use strndup instead of replicating same functionality (Jiri) * Properly handle memory allocation falure (Stanislav) v2 -> v3: https://lore.kernel.org/bpf/20230816165813.3718580-1-davemarchevsky@fb.com/ * Move if (ext->is_weak) test above pr_warn to match existing similar behavior (David Vernet) Signed-off-by: Dave Marchevsky Acked-by: David Vernet Acked-by: Jiri Olsa --- tools/lib/bpf/libbpf.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index b14a4376a86e..2178b28878e2 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -550,6 +550,7 @@ struct extern_desc { int btf_id; int sec_btf_id; const char *name; + char *essent_name; bool is_set; bool is_weak; union { @@ -3770,6 +3771,7 @@ static int bpf_object__collect_externs(struct bpf_object *obj) struct extern_desc *ext; int i, n, off, dummy_var_btf_id; const char *ext_name, *sec_name; + size_t ext_essent_len; Elf_Scn *scn; Elf64_Shdr *sh; @@ -3819,6 +3821,14 @@ static int bpf_object__collect_externs(struct bpf_object *obj) ext->sym_idx = i; ext->is_weak = ELF64_ST_BIND(sym->st_info) == STB_WEAK; + ext_essent_len = bpf_core_essential_name_len(ext->name); + ext->essent_name = NULL; + if (ext_essent_len != strlen(ext->name)) { + ext->essent_name = strndup(ext->name, ext_essent_len); + if (!ext->essent_name) + return -ENOMEM; + } + ext->sec_btf_id = find_extern_sec_btf_id(obj->btf, ext->btf_id); if (ext->sec_btf_id <= 0) { pr_warn("failed to find BTF for extern '%s' [%d] section: %d\n", @@ -7624,7 +7634,8 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, local_func_proto_id = ext->ksym.type_id; - kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &kern_btf, &mod_btf); + kfunc_id = find_ksym_btf_id(obj, ext->essent_name ?: ext->name, BTF_KIND_FUNC, &kern_btf, + &mod_btf); if (kfunc_id < 0) { if (kfunc_id == -ESRCH && ext->is_weak) return 0; @@ -7639,6 +7650,9 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, ret = bpf_core_types_are_compat(obj->btf, local_func_proto_id, kern_btf, kfunc_proto_id); if (ret <= 0) { + if (ext->is_weak) + return 0; + pr_warn("extern (func ksym) '%s': func_proto [%d] incompatible with %s [%d]\n", ext->name, local_func_proto_id, mod_btf ? mod_btf->name : "vmlinux", kfunc_proto_id); @@ -8370,6 +8384,10 @@ void bpf_object__close(struct bpf_object *obj) zfree(&obj->btf_custom_path); zfree(&obj->kconfig); + + for (i = 0; i < obj->nr_extern; i++) + zfree(&obj->externs[i].essent_name); + zfree(&obj->externs); obj->nr_extern = 0;