From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3B82FC35295 for ; Mon, 9 May 2022 01:29:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234320AbiEIBbN convert rfc822-to-8bit (ORCPT ); Sun, 8 May 2022 21:31:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44840 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235668AbiEIAqG (ORCPT ); Sun, 8 May 2022 20:46:06 -0400 Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 70BDC6430 for ; Sun, 8 May 2022 17:42:14 -0700 (PDT) Received: from pps.filterd (m0089730.ppops.net [127.0.0.1]) by m0089730.ppops.net (8.17.1.5/8.17.1.5) with ESMTP id 248L0AE9010450 for ; Sun, 8 May 2022 17:42:13 -0700 Received: from maileast.thefacebook.com ([163.114.130.16]) by m0089730.ppops.net (PPS) with ESMTPS id 3fxhwws2bq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Sun, 08 May 2022 17:42:13 -0700 Received: from twshared0725.22.frc3.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:82::d) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Sun, 8 May 2022 17:42:12 -0700 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id 8E98419A4AD5A; Sun, 8 May 2022 17:42:03 -0700 (PDT) From: Andrii Nakryiko To: , , CC: , Subject: [PATCH bpf-next 7/9] libbpf: provide barrier() and barrier_var() in bpf_helpers.h Date: Sun, 8 May 2022 17:41:46 -0700 Message-ID: <20220509004148.1801791-8-andrii@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220509004148.1801791-1-andrii@kernel.org> References: <20220509004148.1801791-1-andrii@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-GUID: SWIVyP9ulMQX5kbj2SJx9EJ4n6ZSCOhd X-Proofpoint-ORIG-GUID: SWIVyP9ulMQX5kbj2SJx9EJ4n6ZSCOhd X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-08_09,2022-05-06_01,2022-02-23_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Add barrier() and barrier_var() macros into bpf_helpers.h to be used by end users. While a bit advanced and specialized instruments, they are sometimes indispensable. Instead of requiring each user to figure out exact asm volatile incantations for themselves, provide them from bpf_helpers.h. Also remove conflicting definitions from selftests. Some tests rely on barrier_var() definition being nothing, those will still work as libbpf does the #ifndef/#endif guarding for barrier() and barrier_var(), allowing users to redefine them, if necessary. Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/bpf_helpers.h | 24 +++++++++++++++++++ .../selftests/bpf/progs/exhandler_kern.c | 2 -- tools/testing/selftests/bpf/progs/loop5.c | 1 - tools/testing/selftests/bpf/progs/profiler1.c | 1 - tools/testing/selftests/bpf/progs/pyperf.h | 2 -- .../selftests/bpf/progs/test_pkt_access.c | 2 -- 6 files changed, 24 insertions(+), 8 deletions(-) diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h index bbae9a057bc8..fb04eaf367f1 100644 --- a/tools/lib/bpf/bpf_helpers.h +++ b/tools/lib/bpf/bpf_helpers.h @@ -75,6 +75,30 @@ }) #endif +/* + * Compiler (optimization) barrier. + */ +#ifndef barrier +#define barrier() asm volatile("" ::: "memory") +#endif + +/* Variable-specific compiler (optimization) barrier. It's a no-op which makes + * compiler believe that there is some black box modification of a given + * variable and thus prevents compiler from making extra assumption about its + * value and potential simplifications and optimizations on this variable. + * + * E.g., compiler might often delay or even omit 32-bit to 64-bit casting of + * a variable, making some code patterns unverifiable. Putting barrier_var() + * in place will ensure that cast is performed before the barrier_var() + * invocation, because compiler has to pessimistically assume that embedded + * asm section might perform some extra operations on that variable. + * + * This is a variable-specific variant of more global barrier(). + */ +#ifndef barrier_var +#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var)) +#endif + /* * Helper macro to throw a compilation error if __bpf_unreachable() gets * built into the resulting code. This works given BPF back end does not diff --git a/tools/testing/selftests/bpf/progs/exhandler_kern.c b/tools/testing/selftests/bpf/progs/exhandler_kern.c index dd9b30a0f0fc..20d009e2d266 100644 --- a/tools/testing/selftests/bpf/progs/exhandler_kern.c +++ b/tools/testing/selftests/bpf/progs/exhandler_kern.c @@ -7,8 +7,6 @@ #include #include -#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var)) - char _license[] SEC("license") = "GPL"; unsigned int exception_triggered; diff --git a/tools/testing/selftests/bpf/progs/loop5.c b/tools/testing/selftests/bpf/progs/loop5.c index 913791923fa3..1b13f37f85ec 100644 --- a/tools/testing/selftests/bpf/progs/loop5.c +++ b/tools/testing/selftests/bpf/progs/loop5.c @@ -2,7 +2,6 @@ // Copyright (c) 2019 Facebook #include #include -#define barrier() __asm__ __volatile__("": : :"memory") char _license[] SEC("license") = "GPL"; diff --git a/tools/testing/selftests/bpf/progs/profiler1.c b/tools/testing/selftests/bpf/progs/profiler1.c index 4df9088bfc00..fb6b13522949 100644 --- a/tools/testing/selftests/bpf/progs/profiler1.c +++ b/tools/testing/selftests/bpf/progs/profiler1.c @@ -1,6 +1,5 @@ // SPDX-License-Identifier: GPL-2.0 /* Copyright (c) 2020 Facebook */ -#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var)) #define UNROLL #define INLINE __always_inline #include "profiler.inc.h" diff --git a/tools/testing/selftests/bpf/progs/pyperf.h b/tools/testing/selftests/bpf/progs/pyperf.h index 5d3dc4d66d47..6c7b1fb268d6 100644 --- a/tools/testing/selftests/bpf/progs/pyperf.h +++ b/tools/testing/selftests/bpf/progs/pyperf.h @@ -171,8 +171,6 @@ struct process_frame_ctx { bool done; }; -#define barrier_var(var) asm volatile("" : "=r"(var) : "0"(var)) - static int process_frame_callback(__u32 i, struct process_frame_ctx *ctx) { int zero = 0; diff --git a/tools/testing/selftests/bpf/progs/test_pkt_access.c b/tools/testing/selftests/bpf/progs/test_pkt_access.c index 0558544e1ff0..5cd7c096f62d 100644 --- a/tools/testing/selftests/bpf/progs/test_pkt_access.c +++ b/tools/testing/selftests/bpf/progs/test_pkt_access.c @@ -14,8 +14,6 @@ #include #include -#define barrier() __asm__ __volatile__("": : :"memory") - /* llvm will optimize both subprograms into exactly the same BPF assembly * * Disassembly of section .text: -- 2.30.2