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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 08C46CA9EA0 for ; Fri, 18 Oct 2019 19:44:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E28AA2082C for ; Fri, 18 Oct 2019 19:44:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440072AbfJRTo2 (ORCPT ); Fri, 18 Oct 2019 15:44:28 -0400 Received: from www62.your-server.de ([213.133.104.62]:38332 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390538AbfJRTo2 (ORCPT ); Fri, 18 Oct 2019 15:44:28 -0400 Received: from 55.249.197.178.dynamic.dsl-lte-bonding.lssmb00p-msn.res.cust.swisscom.ch ([178.197.249.55] helo=localhost) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1iLYAj-0000DU-Rv; Fri, 18 Oct 2019 21:44:26 +0200 Date: Fri, 18 Oct 2019 21:44:25 +0200 From: Daniel Borkmann To: John Fastabend Cc: andriin@fb.com, ast@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [bpf-next PATCH] bpf: libbpf, support older style kprobe load Message-ID: <20191018194425.GI26267@pc-63.home> References: <157141046629.11948.8937909716570078019.stgit@john-XPS-13-9370> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <157141046629.11948.8937909716570078019.stgit@john-XPS-13-9370> User-Agent: Mutt/1.12.1 (2019-06-15) X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.101.4/25606/Fri Oct 18 10:58:40 2019) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Oct 18, 2019 at 07:54:26AM -0700, John Fastabend wrote: > Following ./Documentation/trace/kprobetrace.rst add support for loading > kprobes programs on older kernels. > > Signed-off-by: John Fastabend > --- > tools/lib/bpf/libbpf.c | 81 +++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 73 insertions(+), 8 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index fcea6988f962..12b3105d112c 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -5005,20 +5005,89 @@ static int determine_uprobe_retprobe_bit(void) > return parse_uint_from_file(file, "config:%d\n"); > } > > +static int use_kprobe_debugfs(const char *name, > + uint64_t offset, int pid, bool retprobe) offset & pid unused? > +{ > + const char *file = "/sys/kernel/debug/tracing/kprobe_events"; > + int fd = open(file, O_WRONLY | O_APPEND, 0); > + char buf[PATH_MAX]; > + int err; > + > + if (fd < 0) { > + pr_warning("failed open kprobe_events: %s\n", > + strerror(errno)); > + return -errno; > + } > + > + snprintf(buf, sizeof(buf), "%c:kprobes/%s %s", > + retprobe ? 'r' : 'p', name, name); > + > + err = write(fd, buf, strlen(buf)); > + close(fd); > + if (err < 0) > + return -errno; > + return 0; > +} > + > static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name, > uint64_t offset, int pid) > { > struct perf_event_attr attr = {}; > char errmsg[STRERR_BUFSIZE]; > + uint64_t config1 = 0; > int type, pfd, err; > > type = uprobe ? determine_uprobe_perf_type() > : determine_kprobe_perf_type(); > if (type < 0) { > - pr_warning("failed to determine %s perf type: %s\n", > - uprobe ? "uprobe" : "kprobe", > - libbpf_strerror_r(type, errmsg, sizeof(errmsg))); > - return type; > + if (uprobe) { > + pr_warning("failed to determine uprobe perf type %s: %s\n", > + name, > + libbpf_strerror_r(type, > + errmsg, sizeof(errmsg))); > + } else { > + /* If we do not have an event_source/../kprobes then we > + * can try to use kprobe-base event tracing, for details > + * see ./Documentation/trace/kprobetrace.rst > + */ > + const char *file = "/sys/kernel/debug/tracing/events/kprobes/"; > + char c[PATH_MAX]; > + int fd, n; > + > + snprintf(c, sizeof(c), "%s/%s/id", file, name); > + > + err = use_kprobe_debugfs(name, offset, pid, retprobe); > + if (err) > + return err; Should we throw a pr_warning() here as well when bailing out? > + type = PERF_TYPE_TRACEPOINT; > + fd = open(c, O_RDONLY, 0); > + if (fd < 0) { > + pr_warning("failed to open tracepoint %s: %s\n", > + c, strerror(errno)); > + return -errno; > + } > + n = read(fd, c, sizeof(c)); > + close(fd); > + if (n < 0) { > + pr_warning("failed to read %s: %s\n", > + c, strerror(errno)); > + return -errno; > + } > + c[n] = '\0'; > + config1 = strtol(c, NULL, 0); > + attr.size = sizeof(attr); > + attr.type = type; > + attr.config = config1; > + attr.sample_period = 1; > + attr.wakeup_events = 1; Is there a reason you set latter two whereas below they are not set, does it not default to these? > + } > + } else { > + config1 = ptr_to_u64(name); > + attr.size = sizeof(attr); > + attr.type = type; > + attr.config1 = config1; /* kprobe_func or uprobe_path */ > + attr.config2 = offset; /* kprobe_addr or probe_offset */ > } > if (retprobe) { > int bit = uprobe ? determine_uprobe_retprobe_bit() > @@ -5033,10 +5102,6 @@ static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name, > } > attr.config |= 1 << bit; > } What happens in case of retprobe, don't you (unwantedly) bail out here again (even through you've set up the retprobe earlier)? > - attr.size = sizeof(attr); > - attr.type = type; > - attr.config1 = ptr_to_u64(name); /* kprobe_func or uprobe_path */ > - attr.config2 = offset; /* kprobe_addr or probe_offset */ > > /* pid filter is meaningful only for uprobes */ > pfd = syscall(__NR_perf_event_open, &attr, >