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 X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DCF25C32789 for ; Tue, 6 Nov 2018 19:14:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A879420827 for ; Tue, 6 Nov 2018 19:14:37 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A879420827 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388567AbeKGElR (ORCPT ); Tue, 6 Nov 2018 23:41:17 -0500 Received: from terminus.zytor.com ([198.137.202.136]:48067 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388107AbeKGElR (ORCPT ); Tue, 6 Nov 2018 23:41:17 -0500 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id wA6JCNiX910638 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 6 Nov 2018 11:12:23 -0800 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id wA6JCN7s910634; Tue, 6 Nov 2018 11:12:23 -0800 Date: Tue, 6 Nov 2018 11:12:23 -0800 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Arnaldo Carvalho de Melo Message-ID: Cc: hpa@zytor.com, wangnan0@huawei.com, ast@kernel.org, namhyung@kernel.org, yhs@fb.com, daniel@iogearbox.net, adrian.hunter@intel.com, ecree@solarflare.com, kafai@fb.com, tglx@linutronix.de, dsahern@gmail.com, acme@redhat.com, mingo@kernel.org, jolsa@kernel.org, linux-kernel@vger.kernel.org Reply-To: kafai@fb.com, ecree@solarflare.com, acme@redhat.com, dsahern@gmail.com, tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, jolsa@kernel.org, wangnan0@huawei.com, hpa@zytor.com, ast@kernel.org, yhs@fb.com, daniel@iogearbox.net, namhyung@kernel.org, adrian.hunter@intel.com To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/urgent] perf augmented_syscalls: Start collecting pathnames in the BPF program Git-Commit-ID: 79ef68c7e1f665578e005b454480b6eca60edabe X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 79ef68c7e1f665578e005b454480b6eca60edabe Gitweb: https://git.kernel.org/tip/79ef68c7e1f665578e005b454480b6eca60edabe Author: Arnaldo Carvalho de Melo AuthorDate: Mon, 5 Nov 2018 12:23:40 -0300 Committer: Arnaldo Carvalho de Melo CommitDate: Mon, 5 Nov 2018 12:41:10 -0300 perf augmented_syscalls: Start collecting pathnames in the BPF program This is the start of having the raw_syscalls:sys_enter BPF handler collecting pointer arguments, namely pathnames, and with two syscalls that have that pointer in different arguments, "open" as it as its first argument, "openat" as the second. With this in place the existing beautifiers in 'perf trace' works, those args are shown instead of just the pointer that comes with the syscalls tracepoints. This also serves to show and document pitfalls in the process of using just that place in the kernel (raw_syscalls:sys_enter) plus tables provided by userspace to collect syscall pointer arguments. One is the need to use a barrier, as suggested by Edward, to avoid clang optimizations that make the kernel BPF verifier to refuse loading our pointer contents collector. The end result should be a generic eBPF program that works in all architectures, with the differences amongst archs resolved by the userspace component, 'perf trace', that should get all its tables created automatically from the kernel components where they are defined, via string table constructors for things not expressed in BTF/DWARF (enums, structs, etc), and otherwise using those observability files (BTF). Cc: Adrian Hunter Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: David Ahern Cc: Edward Cree Cc: Jiri Olsa Cc: Martin KaFai Lau Cc: Namhyung Kim Cc: Wang Nan Cc: Yonghong Song Link: https://lkml.kernel.org/n/tip-37dz54pmotgpnwg9tb6zuk9j@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/examples/bpf/augmented_raw_syscalls.c | 72 ++++++++++++++++++++++++ 1 file changed, 72 insertions(+) diff --git a/tools/perf/examples/bpf/augmented_raw_syscalls.c b/tools/perf/examples/bpf/augmented_raw_syscalls.c index cde91c34b101..90a19336310b 100644 --- a/tools/perf/examples/bpf/augmented_raw_syscalls.c +++ b/tools/perf/examples/bpf/augmented_raw_syscalls.c @@ -37,15 +37,87 @@ struct syscall_exit_args { long ret; }; +struct augmented_filename { + unsigned int size; + int reserved; + char value[256]; +}; + +#define SYS_OPEN 2 +#define SYS_OPENAT 257 + SEC("raw_syscalls:sys_enter") int sys_enter(struct syscall_enter_args *args) { struct { struct syscall_enter_args args; + struct augmented_filename filename; } augmented_args; unsigned int len = sizeof(augmented_args); + const void *filename_arg = NULL; probe_read(&augmented_args.args, sizeof(augmented_args.args), args); + /* + * Yonghong and Edward Cree sayz: + * + * https://www.spinics.net/lists/netdev/msg531645.html + * + * >> R0=inv(id=0) R1=inv2 R6=ctx(id=0,off=0,imm=0) R7=inv64 R10=fp0,call_-1 + * >> 10: (bf) r1 = r6 + * >> 11: (07) r1 += 16 + * >> 12: (05) goto pc+2 + * >> 15: (79) r3 = *(u64 *)(r1 +0) + * >> dereference of modified ctx ptr R1 off=16 disallowed + * > Aha, we at least got a different error message this time. + * > And indeed llvm has done that optimisation, rather than the more obvious + * > 11: r3 = *(u64 *)(r1 +16) + * > because it wants to have lots of reads share a single insn. You may be able + * > to defeat that optimisation by adding compiler barriers, idk. Maybe someone + * > with llvm knowledge can figure out how to stop it (ideally, llvm would know + * > when it's generating for bpf backend and not do that). -O0? ¯\_(ツ)_/¯ + * + * The optimization mostly likes below: + * + * br1: + * ... + * r1 += 16 + * goto merge + * br2: + * ... + * r1 += 20 + * goto merge + * merge: + * *(u64 *)(r1 + 0) + * + * The compiler tries to merge common loads. There is no easy way to + * stop this compiler optimization without turning off a lot of other + * optimizations. The easiest way is to add barriers: + * + * __asm__ __volatile__("": : :"memory") + * + * after the ctx memory access to prevent their down stream merging. + */ + switch (augmented_args.args.syscall_nr) { + case SYS_OPEN: filename_arg = (const void *)args->args[0]; + __asm__ __volatile__("": : :"memory"); + break; + case SYS_OPENAT: filename_arg = (const void *)args->args[1]; + break; + } + + if (filename_arg != NULL) { + augmented_args.filename.reserved = 0; + augmented_args.filename.size = probe_read_str(&augmented_args.filename.value, + sizeof(augmented_args.filename.value), + filename_arg); + if (augmented_args.filename.size < sizeof(augmented_args.filename.value)) { + len -= sizeof(augmented_args.filename.value) - augmented_args.filename.size; + len &= sizeof(augmented_args.filename.value) - 1; + } + } else { + len = sizeof(augmented_args.args); + } + perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, &augmented_args, len); return 0; }