From patchwork Mon Jan 30 14:29:40 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alan Maguire X-Patchwork-Id: 13121263 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 3CB9FC54EED for ; Mon, 30 Jan 2023 14:32:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237690AbjA3OcP (ORCPT ); Mon, 30 Jan 2023 09:32:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49528 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237611AbjA3Ob6 (ORCPT ); Mon, 30 Jan 2023 09:31:58 -0500 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 62E071AF for ; Mon, 30 Jan 2023 06:30:23 -0800 (PST) Received: from pps.filterd (m0246630.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 30UASt3l009421; Mon, 30 Jan 2023 14:29:55 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id; s=corp-2022-7-12; bh=JMJF8ub/wkAFZIrPs/LjPtvvMQMkNicgrQRBj3xEHoM=; b=269IkWkegvBRqvFrZclcpyNWPI93ysfOQ4NTRc1OUs6VPsVNx5w/OOzALwk706jgtoYr 5ENqCnR4Gc49YCchGPdeLLPZ80FxkVEFuZcYlsBBhGpoqrD0Fp+LvcSFS0HOXAoa3hp7 Dw4++2VdHEYvsMGXbaMxGY+161JY7wqqwWc8OeSYRHU+vEWDO4F4mI5Xyy3ivKZ1zAz7 zHvzm6r+UsBh/5IxKcgtRiDop+Kwre0SJWDzW0f3ydWH5PNs3eYCfzkj25gyDr27W8Wt hsnBjZwRpN/+F1smriDGloDsDzebk9hX7jyf24ouecWKvUYTaMRzVW6Mg74ib0WGj0Qv vw== Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.appoci.oracle.com [138.1.114.2]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3ncvn9tysj-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 30 Jan 2023 14:29:54 +0000 Received: from pps.filterd (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (8.17.1.5/8.17.1.5) with ESMTP id 30UDxHdf000723; Mon, 30 Jan 2023 14:29:54 GMT Received: from pps.reinject (localhost [127.0.0.1]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 3nct5462nr-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 30 Jan 2023 14:29:54 +0000 Received: from phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 30UETrIp020648; Mon, 30 Jan 2023 14:29:53 GMT Received: from myrouter.uk.oracle.com (dhcp-10-175-214-73.vpn.oracle.com [10.175.214.73]) by phxpaimrmta01.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTP id 3nct5462kh-1; Mon, 30 Jan 2023 14:29:53 +0000 From: Alan Maguire To: acme@kernel.org, yhs@fb.com, ast@kernel.org, olsajiri@gmail.com, eddyz87@gmail.com, sinquersw@gmail.com, timo@incline.eu Cc: daniel@iogearbox.net, andrii@kernel.org, songliubraving@fb.com, john.fastabend@gmail.com, kpsingh@chromium.org, sdf@google.com, haoluo@google.com, martin.lau@kernel.org, bpf@vger.kernel.org, Alan Maguire Subject: [PATCH v2 dwarves 0/5] dwarves: support encoding of optimized-out parameters, removal of inconsistent static functions Date: Mon, 30 Jan 2023 14:29:40 +0000 Message-Id: <1675088985-20300-1-git-send-email-alan.maguire@oracle.com> X-Mailer: git-send-email 1.8.3.1 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-01-30_13,2023-01-30_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 adultscore=0 malwarescore=0 spamscore=0 phishscore=0 mlxlogscore=999 suspectscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2301300140 X-Proofpoint-GUID: UhlwCWLKh11KW-BOBA4uUTP-JavFay13 X-Proofpoint-ORIG-GUID: UhlwCWLKh11KW-BOBA4uUTP-JavFay13 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org At optimization level -O2 or higher in gcc, static functions may be optimized such that they have suffixes like .isra.0, .constprop.0 etc. These represent - constant propagation (.constprop.0); - interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value (.isra.0) See [1] for details. Currently BTF encoding does not handle such optimized functions that get renamed with a "." suffix such as ".isra.0", ".constprop.0". This is safer because such suffixes can often indicate parameters have been optimized out. This series addresses this by matching a function to a suffixed version ("foo" matching "foo.isra.0") while ensuring that the function signature does not contain optimized-out parameters. Note that if the function is found ("foo") it will be preferred, only falling back to "foo.isra.0" if lookup of the function fails. Addition to BTF is skipped if the function has optimized-out parameters, since the expected function signature will not match. BTF encoding does not include the "."-suffix to be consistent with DWARF. In addition, the kernel currently does not allow a "." suffix in a BTF function name. A problem with this approach however is that BTF carries out the encoding process in parallel across multiple CUs, and sometimes a function has optimized-out parameters in one CU but not others; we see this for NF_HOOK.constprop.0 for example. So in order to determine if the function has optimized-out parameters in any CU, its addition is not carried out until we have processed all CUs and are about to merge BTF. At this point we know if any such optimizations have occurred. Patches 1-4 handle the optimized-out parameter identification and matching "."-suffixed functions with the original function to facilitate BTF encoding. Patch 5 addresses a related problem - it is entirely possible for a static function of the same name to exist in different CUs with different function signatures. Because BTF does not currently encode any information that would help disambiguate which BTF function specification matches which static function (in the case of multiple different function signatures), it is best to eliminate such functions from BTF for now. The same mechanism that is used to compare static "."-suffixed functions is re-used for the static function comparison. A superficial comparison of number of parameters/parameter names is done to see if such representations are consistent, and if inconsistent prototypes are observed, the function is flagged for exclusion from BTF. When these methods are combined - the additive encoding of "."-suffixed functions and the subtractive elimination of functions with inconsistent parameters - we see an overall drop in the number of functions in vmlinux BTF, from 51150 to 49871. Changes since v1 [2] - Eduard noted that a DW_AT_const_value attribute can signal an optimized-out parameter, and that the lack of a location attribute signals optimization; ensure we handle those cases also (Eduard, patch 1). - Jiri noted we can have inconsistencies between a static and non-static function; apply the comparison process to all functions (Jiri, patch 5) - segmentation fault was observed when handling functions with > 10 parameters; needed parameter comparison loop to exit at BTF_ENCODER_MAX_PARAMETERS (patch 5) - Kui-Feng Lee pointed out that having a global shared function tree would lead to a lot of contention; here a per-encoder tree is used, and once the threads are collected the trees are merged. Performance numbers are provided in patch 5 (Kui-Feng Lee, patches 4/5) Alan Maguire (5): dwarves: help dwarf loader spot functions with optimized-out parameters btf_encoder: refactor function addition into dedicated btf_encoder__add_func btf_encoder: rework btf_encoders__*() API to allow traversal of encoders btf_encoder: represent "."-suffixed functions (".isra.0") in BTF btf_encoder: delay function addition to check for function prototype inconsistencies btf_encoder.c | 392 ++++++++++++++++++++++++++++++++++++++++++++++++--------- btf_encoder.h | 6 - dwarf_loader.c | 125 ++++++++++++++++-- dwarves.h | 8 +- pahole.c | 14 +-- 5 files changed, 464 insertions(+), 81 deletions(-)