From patchwork Wed Apr 12 21:04:23 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Song Liu X-Patchwork-Id: 13209517 X-Patchwork-Delegate: bpf@iogearbox.net 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 1B78FC77B77 for ; Wed, 12 Apr 2023 21:11:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229949AbjDLVLc convert rfc822-to-8bit (ORCPT ); Wed, 12 Apr 2023 17:11:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229895AbjDLVLb (ORCPT ); Wed, 12 Apr 2023 17:11:31 -0400 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B82D259E3 for ; Wed, 12 Apr 2023 14:11:30 -0700 (PDT) Received: from pps.filterd (m0044010.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 33CI9ACJ010159 for ; Wed, 12 Apr 2023 14:04:39 -0700 Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3pwqspvujh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 12 Apr 2023 14:04:38 -0700 Received: from twshared21760.39.frc1.facebook.com (2620:10d:c085:208::f) by mail.thefacebook.com (2620:10d:c085:21d::6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.17; Wed, 12 Apr 2023 14:04:38 -0700 Received: by devbig932.frc1.facebook.com (Postfix, from userid 4523) id 7CBAB1B0AF061; Wed, 12 Apr 2023 14:04:32 -0700 (PDT) From: Song Liu To: CC: , , , , Song Liu Subject: [PATCH bpf-next 3/3] selftests/bpf: Keep the loop in bpf_testmod_loop_test Date: Wed, 12 Apr 2023 14:04:23 -0700 Message-ID: <20230412210423.900851-4-song@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230412210423.900851-1-song@kernel.org> References: <20230412210423.900851-1-song@kernel.org> MIME-Version: 1.0 X-FB-Internal: Safe X-Proofpoint-ORIG-GUID: bp3lVbQxVRyizfaL0LqE8hoEHFy2SuQX X-Proofpoint-GUID: bp3lVbQxVRyizfaL0LqE8hoEHFy2SuQX X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-04-12_11,2023-04-12_01,2023-02-09_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Some compilers (for example clang-15) optimize bpf_testmod_loop_test and remove the loop: gcc version (gdb) disassemble bpf_testmod_loop_test Dump of assembler code for function bpf_testmod_loop_test: 0x0000000000000570 <+0>: callq 0x575 0x0000000000000575 <+5>: xor %eax,%eax 0x0000000000000577 <+7>: test %edi,%edi 0x0000000000000579 <+9>: jle 0x587 0x000000000000057b <+11>: xor %edx,%edx 0x000000000000057d <+13>: add %edx,%eax 0x000000000000057f <+15>: add $0x1,%edx 0x0000000000000582 <+18>: cmp %edx,%edi 0x0000000000000584 <+20>: jne 0x57d 0x0000000000000586 <+22>: retq 0x0000000000000587 <+23>: retq clang-15 version (gdb) disassemble bpf_testmod_loop_test Dump of assembler code for function bpf_testmod_loop_test: 0x0000000000000450 <+0>: nopl 0x0(%rax,%rax,1) 0x0000000000000455 <+5>: test %edi,%edi 0x0000000000000457 <+7>: jle 0x46b 0x0000000000000459 <+9>: lea -0x1(%rdi),%eax 0x000000000000045c <+12>: lea -0x2(%rdi),%ecx 0x000000000000045f <+15>: imul %rax,%rcx 0x0000000000000463 <+19>: shr %rcx 0x0000000000000466 <+22>: lea -0x1(%rdi,%rcx,1),%eax 0x000000000000046a <+26>: retq 0x000000000000046b <+27>: xor %eax,%eax 0x000000000000046d <+29>: retq Note: The jne instruction is removed in clang-15 version. Force the compile to keep the loop by making sum volatile. Signed-off-by: Song Liu --- tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c index 7999476b9446..c5ad39bbe9af 100644 --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c @@ -130,7 +130,11 @@ bpf_testmod_test_btf_type_tag_percpu_2(struct bpf_testmod_btf_type_tag_3 *arg) { noinline int bpf_testmod_loop_test(int n) { - int i, sum = 0; + /* Make sum volatile, so smart compilers, such as clang, will not + * optimize the code by removing the loop. + */ + volatile int sum = 0; + int i; /* the primary goal of this test is to test LBR. Create a lot of * branches in the function, so we can catch it easily.