From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) (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 4CA1B64A8F; Tue, 20 May 2025 08:59:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=205.220.165.32 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747731597; cv=fail; b=sfbRVFp45xPqanjD+SCrlrXG5tYzzY6CI/GKuVW1YKMrhJtPI5iT7oCI9+LBSGUj8HRlxljFy3hpkRHDKLvQfXO269VcBaxbGXqKrQb+ps21uu51mDMm6PedSCE0eMKAHiY1x63jlJiw+GhsGiKRmcHvxl0nP4dCfFBLHxAuNpI= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747731597; c=relaxed/simple; bh=SW5aERmtjLBaU0swQZ/SDuI0izmxHP9mmu01vk6I/Lo=; h=Message-ID:Date:Subject:From:To:Cc:References:In-Reply-To: Content-Type:MIME-Version; b=r/MrupxmILkz1JEF0LLn4ba9En71+pxp2k4M3hQybC9/WI8YBTo14TW+KwdSVrO+0hvGCzV7OBpBHeEOK8mhG4I28vzQomGLZ9CWnCdFGaSFJflYkgvusXU3Y+O+BJzwjNO3sdAFWOfDqIyYVmi+WouufvYEDgo+xScyn7SX6OM= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com; spf=pass smtp.mailfrom=oracle.com; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b=UEHY3VSO; dkim=pass (1024-bit key) header.d=oracle.onmicrosoft.com header.i=@oracle.onmicrosoft.com header.b=bqTOVOll; arc=fail smtp.client-ip=205.220.165.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oracle.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="UEHY3VSO"; dkim=pass (1024-bit key) header.d=oracle.onmicrosoft.com header.i=@oracle.onmicrosoft.com header.b="bqTOVOll" Received: from pps.filterd (m0246617.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 54K8fWV9022612; Tue, 20 May 2025 08:59:43 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s= corp-2025-04-25; bh=u/0UyvJ+/9JApst1nMpDzLa1irscVb/2s35VeHMdmlI=; b= UEHY3VSOBx9DgcdclDxTKCah4aM4u5lmvbUZz5HcRa1Og0VL1RrdmRXrsB+L4MAd MJ3T/+yqu2vUsZ1F0ApWurWkyIB+AGYK/RBgnVVSSMRLdHemkjw//Y7eADbHbjjz opKOomm/6IrCN7bXvB+Zq3IFDiPqwP2lqMEn6lpgaFfI6nED0MR9rDsfW1c5iLWY wxr943e/kCY22ixKO0QEmh1gLuoyvUKJocPLLSZ9IfodicCU7Ts48fQKSNDeNKcK br5kuqRh1cFssL8tqBjSBwwZUDNvy41Y70qAAKnMGU2IqUd6MoTLOlyN1vv7Sb62 JNZBwOLlWUC5ve2BhiFAow== Received: from phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta02.appoci.oracle.com [147.154.114.232]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 46pk0vvwm8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 20 May 2025 08:59:42 +0000 (GMT) Received: from pps.filterd (phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (8.18.1.2/8.18.1.2) with ESMTP id 54K8Hcsj002414; Tue, 20 May 2025 08:59:41 GMT Received: from nam10-bn7-obe.outbound.protection.outlook.com (mail-bn7nam10lp2045.outbound.protection.outlook.com [104.47.70.45]) by phxpaimrmta02.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 46pgw7g7wy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 20 May 2025 08:59:41 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=fjW5T1JyccTROmTFtiFJF5qAhLRvATBv/kFGPOaXUJ3v/2AS/NBIMsUTt4n4AY+7ifBFJnGKrwmaAnkafI4Q2/Ls0Egdg4/SpKX1GBgsHlLSS9XDvSFLDupZ7n5le3L786abBvnqPvmr+1JvRwJXkhxpmXbxePajhcaR4cNnA9q/zCxjo0HIG4OKO7FP7b1i1ahPrTeiUCBG5oxKn7P1ZKXTaO5nRD8coeM470IM1DiMJRqTUgxT2XT/oe5y1cw3ylbBpY+Xu6UNX4GijN+ft/sZxaJlOuBedbieEB0TL5zlRN81iCqtuGcJcBbShwvWLtQC84MWvQDrcFtcfVGRtA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=u/0UyvJ+/9JApst1nMpDzLa1irscVb/2s35VeHMdmlI=; b=COdYOvLJAFyriJEVIQPqRV6m94CnvvwVC2TOBZlhph5m/22a6HdChia3jXD3bBDm4IWG839KI1/vHnmCb/EpR4uQtVCyzojs4ZpgOJk4Y8Ena/IrF91I5WCGE4yeN67idJD+fS+GTql0zua463CHeJ4IvEIIkr2zFR6t+JUeZ214OqsfdD+Rg4KZiglU19jHWxK2Pdxc5swSQUy1P8yCvC8mAgS6SA8DtvlnBY4Es4J8OtI0U7BzSR4H/AwfTVH1JeNuhkrZULoV8ioZ3GL7goMz/PN1VhuF+D5knIWYJb3jNkwZ8AQPsT1SnfBgQhhcoKe7B0hYFO8RJdy1bA5HCg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=u/0UyvJ+/9JApst1nMpDzLa1irscVb/2s35VeHMdmlI=; b=bqTOVOll7n9ejVtOqNcCls9t4Wf6Y4S6rXT23330v0g3jTonjT46hRhnJ9AVin6aO8o4DgUtN/SLK7iaKMHoMoE4xMvb3Hu6uvLJB/U6fCb38W1q9DVG9rZmD0PAgAUYbC6yyta3yPolXLDCEFp2kc5qg6XpmGQ6L1F6a09I5PY= Received: from BLAPR10MB5267.namprd10.prod.outlook.com (2603:10b6:208:30e::22) by SJ5PPFA7DBF91DC.namprd10.prod.outlook.com (2603:10b6:a0f:fc02::7c1) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8746.31; Tue, 20 May 2025 08:59:33 +0000 Received: from BLAPR10MB5267.namprd10.prod.outlook.com ([fe80::682b:c879:9f97:a34f]) by BLAPR10MB5267.namprd10.prod.outlook.com ([fe80::682b:c879:9f97:a34f%4]) with mapi id 15.20.8699.022; Tue, 20 May 2025 08:59:33 +0000 Message-ID: <9a41b21f-c0ae-4298-bf95-09d0cdc3f3ab@oracle.com> Date: Tue, 20 May 2025 09:59:27 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [RFC bpf-next 0/3] bpf: handle 0-sized structs properly From: Alan Maguire To: Andrii Nakryiko Cc: martin.lau@linux.dev, ast@kernel.org, andrii@kernel.org, tony.ambardar@gmail.com, alexis.lothore@bootlin.com, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, bpf@vger.kernel.org, dwarves@vger.kernel.org References: <20250508132237.1817317-1-alan.maguire@oracle.com> <8faae89d-3515-480c-9abe-4d0e7514e41b@oracle.com> Content-Language: en-GB In-Reply-To: <8faae89d-3515-480c-9abe-4d0e7514e41b@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO4P123CA0535.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:2c5::20) To BLAPR10MB5267.namprd10.prod.outlook.com (2603:10b6:208:30e::22) Precedence: bulk X-Mailing-List: dwarves@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BLAPR10MB5267:EE_|SJ5PPFA7DBF91DC:EE_ X-MS-Office365-Filtering-Correlation-Id: ce237778-d657-4444-ae82-08dd977ca373 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?em1TM1NrTlplVUVyN2tFbUFMV2JMMi9LUU1GYnR2V05DZFpwMDVZWUhHUlcr?= =?utf-8?B?TmtiamkzZ2JQemxxWkRRcnE4UW5wemt5SDY3WDRGdy9GclpEamt6b29Qc2ZF?= =?utf-8?B?ZGd0Tm45VEY5a2NmdDc5Yzg3NEJPUThjZzlqSUpCeWdZenJTUldSRXRCWVdS?= =?utf-8?B?ZHpqQmI0ZlJOSXJKYzFlQW1tejRFQmQ1UnNuS0IxSG9wZm4rR1puSHd4ZHYz?= =?utf-8?B?d0lHbW5xQ2NhNTUvRDlvUzdyN1B4ZzBZVTZIVkFZZW1tdlFDZkRFclZEQTFo?= =?utf-8?B?c0ptQTBMUkZJZy95TEdDSnlLVVJnZFgxcmxyTWlacFFWRWJMVjVSSWdoY0VP?= =?utf-8?B?aEh4YVVTWCs1TlhqaTZGd3NiRW9STTFBNUdsR1hNdXVFQi9tblR4bzFkdFJN?= =?utf-8?B?bEhwYWtFT0ZsYjZsNlovYjBjQ3liNzFQTUhOQmplSXpIWVExV3FrWkhjazFo?= =?utf-8?B?bEMwN0c2ZmxIT0UzV1NDeFU3Zk5WUVpMdGRYWTBRRENxbFhWZC9aNHMydk1N?= =?utf-8?B?Mzd2SmxYQjNkS3dWajBac1ZMZE9xUGRIVmhlUG51ZTZxc09jRWdudGxzeXVS?= =?utf-8?B?dU1XQkErcC92Qkl2R1VacjFOQ3dDVklVaDZ4OHl6WjlzNDUwM3kxdjlZYVJV?= =?utf-8?B?T1N5SEtpT2pOZlJvaHBTUVZHdW5xRmF1T2phZHA1NjFST0xEcUZiR2Zrd3o2?= =?utf-8?B?Z2tPMU16L2cwbGo3TFBjdjBjanIxUjVPa3FxVmNOTVlWT3orTnpLQmx5Q1Fv?= =?utf-8?B?ZzZ5MEd6TFllYURHaDZCbHg3cmJMMkZva28xakxmcmFIR3FhS3VJZTk3bVZ2?= =?utf-8?B?dUJCckNvdVF4ZVVwU2s5SFB3M1oyWVQ3cEFhRElzRTJvQWlFdzRxeTdBekVG?= =?utf-8?B?MXhyVytzcTdtVjRnWjd1TFhhVGFsQlJtWVlsSDZ1dmZIMkNScFZrc0Z4cVNI?= =?utf-8?B?Q0dtRnJibG11Z3pFKzdEUk10TGZZaU1HeWNBd2tiZlVhQXYrQ09KWUE2dXlk?= =?utf-8?B?UGdTMlVNQjBRdTJWR3NBR2xtOTJVdjJDQWJXayswRjRJM0RPa3hvaG1oZFJS?= =?utf-8?B?aEhHejAyWjloVlR3bnRGYTQxK2tBRmhuZEtzUlJVRXdVbElDbXYwZ0ZDMkkw?= =?utf-8?B?V0tmR1JNblBFUmQrd29COHRkK3Q2Nk53WVBvTkhCeThtUUtZS3VYaGYrUitG?= =?utf-8?B?MDQyYW9EZ1ZVL3F0UTFtVk5lNkhEQzhYTm9lV1J6SmpEYU9UTEdva3lBOVZK?= =?utf-8?B?UGtBVlp6azR4OENCc1BXemV5VHFEYWpyRlp0SGpzR0xtL1l4UUx2cjUwK0lE?= =?utf-8?B?cGZPN29VYUN4SUdKYmFuVGVkbEFOcW1xT0VpQUVOMC95SVN6Y3A1cEozSjFH?= =?utf-8?B?VG1mYXlkdkNZTFpOL1lOdEdiQWlmQTF4QnpPWXRWZGdRcFgxNlk0Q2dXd2ds?= =?utf-8?B?OThDV1djYitQMkFmZS80citmWGhCY3VmRE1rZEFOc3A2UUxkNHhHVzVRbGpP?= =?utf-8?B?RVE5dFgvanR5ZlZMdmVGNXdhVFpzK3RicS9RMlRZUnMrR0JSZllrMGwwakxI?= =?utf-8?B?TDR4ejFMSmtLU3A3MnJFckN4WVlqZmRDNEc4UEhsVEhGRklKdnFQTFlYOUFw?= =?utf-8?B?dEJJc0k5Y3BiK3BBUXZKcUdtRUI4RktidjZleUhkaW0vR29zRDJTQ1hEUDFp?= =?utf-8?B?akVQbXRBT3F2UlZLUnBQdTlLS1g1eUJDdjlOYnVEUzNJMlc1MmpMQ1JBT1Fa?= =?utf-8?B?aGdLalRCS3NwcW1HeHJLUEptVU8wSWVITVBvdzk1UEw2Y0xRRnZOanVCUlBJ?= =?utf-8?Q?A4oMuGJ9XZ72Amw5rIO5hV4L0mBmB047SQDO8=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BLAPR10MB5267.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(376014)(7416014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VmlGS1REaHpaMlJUOVdoKzhka21kSlVpRHVwTnFqSEFyaFBQQnlCd3ZmZWdx?= =?utf-8?B?L0hacEczdXdCVndabnNqVFZzWEdPT1c0bGU3U0hRSEk1VDVoekl6WTV5b2hu?= =?utf-8?B?VUJRZW8yQmRuajFGVU9SMzkvUjdYUU9Gamt4blV1K1FNVGVWblFKamZzalNp?= =?utf-8?B?clRnOUYrYWRuRmlWWDViWVg2MVkzazVSV05wOGcySFUwK2Zua2hieitvQzhD?= =?utf-8?B?bkFRWUgvZ05pLzJnZllaS3NOMExGUlpnbUVzSWlNanQyK0JxMU1DY1VYSE8x?= =?utf-8?B?clFEWGJwbGt3a0JLc3JzOHVRdjBwSlRpT2Q4bThiWmpKVDV5SGpLRjRmU2d2?= =?utf-8?B?UWc4RklzWHlkbGdPQjlnTTlheDQyVGNhaTBvcHRYdE1mRHdQTnRHV0hjSUZR?= =?utf-8?B?TXZ3YytIOFV5R0I1ZE5XS0Ftb3dtYXk3QVQ5eFlXenFrTVhFVmxGdm85am9X?= =?utf-8?B?ZG1hT05xMU5QVnZtU1VCRStPV1k1OHFvRFkxTEowQUVoZ1l4TlFta2VDM3Rj?= =?utf-8?B?VTBzSURIY1F6TDlhTDJUYzdWb3oySWFkSlJJOWhJSlVRanRSblJQWWFjbVg1?= =?utf-8?B?VTZPOVBob20yRWRRTTQyVi9rdTZ0bHo4UjFnR0ZxRktUcWVkN3NweHZDWERR?= =?utf-8?B?aHlmYkUzZWJZN0t0SnQ3aEl5L3pEb3ZoWmp3blVFQlpUSklzL3A2Y1l5aUJZ?= =?utf-8?B?N1hZMXJNOHBrRFJqSURMd253RE8yazd2WUYwbHEvVmxkZGIxaStzczk2WUhN?= =?utf-8?B?QktaNjgvL0lyU1JzOHFmQWNYcHc0ZERoSFFueElhYTRJRkx5SEQ4c2d1WkdB?= =?utf-8?B?dUw1ZDJSa0ZtT3FIOTdzNTdyaXJBcnJTNGg3SmJaS2RqWFIwV1VwbHQ2UU81?= =?utf-8?B?L1JxYXUya0c0MXpTcFJSRWFVKyszMXNBY05SbmhOS1E2NFBVUE9MOGVWRjBn?= =?utf-8?B?VFJ0Q1kyWWFsZHZlM2FjcHd4VE4vL1FJTlFQaGYwK2o4VjdxQ2hQbHIvY0Fp?= =?utf-8?B?TS9aRURvMnZsOVR2bjYveFNaU0h1azZxcVpyL3Y2eGY2Y05wblovTlA3RmdM?= =?utf-8?B?UGZOTWhxK1BlR2E1UGl2cDQvSWRacFE5eXByTytoMlN2YU0wWjZSK25yTG5T?= =?utf-8?B?bXF1WUs3YTN1eUpnd25sMHc4VUczNnhoMGVaU2YveWx5aVpTNWNzV2lBclRh?= =?utf-8?B?UXV6eWNMY29Lajc1a2gyZzVLbkIrV1NsOVhaTklkMDRJeGJyM043WTZVN2V1?= =?utf-8?B?VXp5TVQ0Wm1pQlh1Zk5jSmJYbWNaa2t3RzM4Q0RhME5wOGNYSnUyYVpXOXJq?= =?utf-8?B?Z2hlYTREQTk4WVl2Y29ONndaaG5ub1NVOE04ZzNJWUZWYjd5b1NlVWRLeXB5?= =?utf-8?B?cEJWMEIrbXp2bndQY3ZwdjZIQ1dhRDJ3eDZwUTlpL0NRUDA5b084WGJmb2tV?= =?utf-8?B?bjFFTHpXRDNsTHZJZEplRFI0VHQ4Rks1QUhUcHd5SXZzUlhYS3ZUdlRqOGY4?= =?utf-8?B?OUFLZklrYkZmNFJvTVRLN2UzdFk1RC9INUhLV013enFXcE5lbS81TCtsdFZ5?= =?utf-8?B?ejZsd3BPMEpvMFVDVXlnVk1pdmhJM0RSR2ltQ0QvaEs5TFBQQTJwd2QvMDNF?= =?utf-8?B?WlR6QTllM1pBdGFrVkRaZjhKR0pLbm5aT002Nmo1SUYvanJxUytOYjI4MmhF?= =?utf-8?B?d0FVWmpGSlNIWWkrQ1hBdHdmYmd2ZmUxZitSbEtYTUxFekJzUXJOaWx6NUFs?= =?utf-8?B?aWE1VlF4WmI2ajdZUGRSR0gzS1Rjb21pZ3hORkNadm5ickMydEdwTWdnM3l0?= =?utf-8?B?OEc5ektpZ2FqNWl3aWZGelk2VnJBZ1ZjTHN5LzVDMitlYXBYZlNBZUM4VzQr?= =?utf-8?B?QUxFaGdFSnZRMUVkTll0Vm5WMmtkZFJtSmIzc01qUUpNOWl4b1l3SnV1Zkk1?= =?utf-8?B?QmNNTjhpMWRybzBLL1h2NUw1OGc4MlI5RlRDRU5zUXRQbXJBK1pEVmFOamhH?= =?utf-8?B?cmVnYlpSNWg3SFhqcnR1Rm4yTXMwZDczcllDRU1abnBHazJBMDhiQTJhWUMr?= =?utf-8?B?Yyt6akoyVU1SRkpEK0FrK2p1Wmd0QWN1dDNLeFhVNXFKcVJneHZxOGFFSE1w?= =?utf-8?B?RUpodFV5cC9jTHp0Z2xpS3czMHNoTHAvckNYS1hIRmU3WnRZcFkvTE9ZVHlh?= =?utf-8?B?Qnc9PQ==?= X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: 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 X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: ce237778-d657-4444-ae82-08dd977ca373 X-MS-Exchange-CrossTenant-AuthSource: BLAPR10MB5267.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 May 2025 08:59:33.3245 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: p18XXm6j1NBdNBBDhgaroVs7LCByqwEiJebw757eq5rhkg+dbYquzfuKqJcpnAt0KgOiMM+kLgtGC5VreXBhjA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ5PPFA7DBF91DC X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-20_04,2025-05-16_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 bulkscore=0 mlxlogscore=999 phishscore=0 adultscore=0 suspectscore=0 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2505070000 definitions=main-2505200073 X-Proofpoint-ORIG-GUID: 4WDS_esaOOj3SximPqttoEG6ak_ZbGRi X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTIwMDA3MyBTYWx0ZWRfX14IDTxZ04a8J G/DKf+1LdLkF1lb1zZ5Gmh14kG1Bh3kPtBI/zxnJ8e0PGpbm5GBAZlXdoZrbqVJ3kfmc9xqyfCu pNcGuaAlNVNMMuwLO/01YLkcjk1IPxgnYtWz8vB7tKYAxceTJkb5WQ2t9fLAigNLPE48DkUFLBx cB2Oi3qtCzhHI78neXOmKNC7bgjG+QcLt4va0bC4GtGgEhpNdfwCYctfualJT201+5gZsZY8Djx +qS3YZewoeiZZ/EmfOCw+8jZZsQc1OsB0TVbgYpfcTvmjhQFZ+JVSJBQDQZAYbFSCJ8pF96FnbI w6d8ZJkioNFXKioo3p9b4GNn3yr9FzeGBVeFW8dKhJmo/OKyclUWEarD+CKJ6KSCUnwh/25JFGn ybdsrAuVB9JTQ/34TQlebGqeqdZHKjQQXmWqjbEnpxA7TDkIc6n+56h0uOozBGuD3C90VoCA X-Authority-Analysis: v=2.4 cv=CMIqXQrD c=1 sm=1 tr=0 ts=682c447e cx=c_pps a=OOZaFjgC48PWsiFpTAqLcw==:117 a=OOZaFjgC48PWsiFpTAqLcw==:17 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=pGLkceISAAAA:8 a=yPCof4ZbAAAA:8 a=9hUN_IrMVSbGpGRg_woA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: 4WDS_esaOOj3SximPqttoEG6ak_ZbGRi On 15/05/2025 11:56, Alan Maguire wrote: > On 09/05/2025 19:40, Andrii Nakryiko wrote: >> On Thu, May 8, 2025 at 6:22 AM Alan Maguire wrote: >>> >>> When testing v1 of [1] we noticed that functions with 0-sized structs >>> as parameters were not part of BTF encoding; this was fixed in v2. >>> However we need to make sure we handle such zero-sized structs >>> correctly since they confound the calling convention expectations - >>> no registers are used for the empty struct so this has knock-on effects >>> for subsequent register-parameter matching. >> >> Do you have a list (or at least an example) of the function we are >> talking about, just curious to see what's that. >> >> The question I have is whether it's safe to assume that regardless of >> architecture we can assume that zero-sized struct has no effect on >> register allocation (which would seem logical, but is that true for >> all ABIs). >> > > I've been investigating this a bit, specifically in the context of s390 > where we saw the test failure. The actual kernel function where I first > observed the zero-sized struct in practice is > > static int __io_run_local_work(struct io_ring_ctx *ctx, io_tw_token_t > tw, int min_events, int max_events); > > In s390 DWARF, we see the following representation for it: > > <1><6f7f788>: Abbrev Number: 104 (DW_TAG_subprogram) > <6f7f789> DW_AT_name : (indirect string, offset: 0x2c47f5): > __io_run_local_work > <6f7f78d> DW_AT_decl_file : 1 > <6f7f78e> DW_AT_decl_line : 1301 > <6f7f790> DW_AT_decl_column : 12 > <6f7f791> DW_AT_prototyped : 1 > <6f7f791> DW_AT_type : <0x6f413a2> > <6f7f795> DW_AT_low_pc : 0x99c850 > <6f7f79d> DW_AT_high_pc : 0x2b2 > <6f7f7a5> DW_AT_frame_base : 1 byte block: 9c > (DW_OP_call_frame_cfa) > <6f7f7a7> DW_AT_GNU_all_call_sites: 1 > <6f7f7a7> DW_AT_sibling : <0x6f802e6> > <2><6f7f7ab>: Abbrev Number: 53 (DW_TAG_formal_parameter) > <6f7f7ac> DW_AT_name : ctx > <6f7f7b0> DW_AT_decl_file : 1 > <6f7f7b1> DW_AT_decl_line : 1301 > <6f7f7b3> DW_AT_decl_column : 52 > <6f7f7b4> DW_AT_type : <0x6f6882b> > <6f7f7b8> DW_AT_location : 0x2babcbe (location list) > <6f7f7bc> DW_AT_GNU_locviews: 0x2babcac > <2><6f7f7c0>: Abbrev Number: 135 (DW_TAG_formal_parameter) > <6f7f7c2> DW_AT_name : tw > <6f7f7c5> DW_AT_decl_file : 1 > <6f7f7c6> DW_AT_decl_line : 1301 > <6f7f7c8> DW_AT_decl_column : 71 > <6f7f7c9> DW_AT_type : <0x6f6833e> > <6f7f7cd> DW_AT_location : 2 byte block: 73 0 (DW_OP_breg3 > (r3): 0) > > > ..i.e. we are using the expected calling-convention register (r3) here > for the zero-sized struct parameter. > > Contrast this with x86_64 and aarch64, where regardless of -O level we > appear to use an offset from the frame ptr to reference the zero-sized > struct. As a result the next parameter after the zero-sized struct uses > the next available calling-convention register (%rdi if the zero-sized > struct is the first arg, %rsi if it was the second etc) that was unused > by the zero-sized struct parameter. > > I don't see anything in the ABI specs which covers this scenario > exactly; I suspect the 0-sized object handling in cases other than s390 > is just using the usual > register size aggregate object handling > (passing a large struct as a parameter), and in s390 it's not. > > So long story short, we may need to take an arch-specific approach here > unfortunately. Great that CI flagged this as an issue too! > > Alan > > I discussed this with Jose, and the gcc behaviour with zero-sized structs varies a bit between architectures. Given that complexity, my inclination would be to class functions with 0-sized struct parameters as having inconsistent representations. They can then be tackled by adding location info on a per-site basis later as part of the inline-related work. For now we would just not emit BTF for them, since without that site-specific analysis we can't be sure from function signature alone where parameters are stored. In practice this means leaving one function out of kernel BTF. So long story short, I think it might make sense to withdraw this series for now and see if we can tweak Tony's patch to class functions with 0-sized parameters as inconsistent as the v1 version did, meaning they don't get a BTF representation. Thanks! Alan > > >> BTW, while looking at patch #2, I noticed that >> btf_distill_func_proto() disallows functions returning >> struct-by-value, which seems overly aggressive, at least for structs >> of up to 8 bytes. So maybe if we can validate that both cases are not >> introducing any new quirks across all supported architectures, we can >> solve both limitations? >> >> P.S., oh, and s390x selftest (test_struct_args) isn't happy, please check. >> >> >>> >>> Patch 1 updates BPF_PROG2() to handle the zero-sized struct case. >>> Patch 2 makes 0-sized structs a special case, allowing them to exist >>> as parameter representations in BTF without failing verification. >>> Patch 3 is a selftest that ensures the parameters after the 0-sized >>> struct are represented correctly. >>> >>> [1] https://lore.kernel.org/dwarves/20250502070318.1561924-1-tony.ambardar@gmail.com/ >>> >>> Alan Maguire (3): >>> libbpf: update BPF_PROG2() to handle empty structs >>> bpf: allow 0-sized structs as function parameters >>> selftests/bpf: add 0-length struct testing to tracing_struct tests >>> >>> kernel/bpf/btf.c | 2 +- >>> tools/lib/bpf/bpf_tracing.h | 6 ++++-- >>> .../selftests/bpf/prog_tests/tracing_struct.c | 2 ++ >>> tools/testing/selftests/bpf/progs/tracing_struct.c | 11 +++++++++++ >>> tools/testing/selftests/bpf/test_kmods/bpf_testmod.c | 12 ++++++++++++ >>> 5 files changed, 30 insertions(+), 3 deletions(-) >>> >>> -- >>> 2.39.3 >>> > >