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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 6E2CEC6778F for ; Fri, 27 Jul 2018 19:31:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E69C20842 for ; Fri, 27 Jul 2018 19:31:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1E69C20842 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=iogearbox.net 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 S2389292AbeG0Uy3 (ORCPT ); Fri, 27 Jul 2018 16:54:29 -0400 Received: from www62.your-server.de ([213.133.104.62]:56673 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388467AbeG0Uy2 (ORCPT ); Fri, 27 Jul 2018 16:54:28 -0400 Received: from [78.46.172.2] (helo=sslproxy05.your-server.de) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.85_2) (envelope-from ) id 1fj8S9-0000nV-7y; Fri, 27 Jul 2018 21:31:05 +0200 Received: from [99.0.85.34] (helo=localhost.localdomain) by sslproxy05.your-server.de with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1fj8S8-00054A-Ty; Fri, 27 Jul 2018 21:31:05 +0200 Subject: Re: [PATCH] perf build: Build error in libbpf missing initialization To: Jakub Kicinski , Thomas Richter Cc: ast@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, heiko.carstens@de.ibm.com, brueckner@linux.vnet.ibm.com, schwidefsky@de.ibm.com References: <20180727082126.87530-1-tmricht@linux.ibm.com> <20180727105923.2d5da6aa@cakuba.netronome.com> From: Daniel Borkmann Message-ID: Date: Fri, 27 Jul 2018 21:31:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20180727105923.2d5da6aa@cakuba.netronome.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.100.0/24788/Fri Jul 27 18:45:51 2018) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/27/2018 07:59 PM, Jakub Kicinski wrote: > On Fri, 27 Jul 2018 10:21:26 +0200, Thomas Richter wrote: >> In linux-next tree compiling the perf tool with additional make flags >> "EXTRA_CFLAGS="-Wp,-D_FORTIFY_SOURCE=2 -O2" >> causes a compiler error. It is the warning >> 'variable may be used uninitialized' >> which is treated as error: >> >> I compile it using a FEDORA 28 installation, my gcc compiler version: >> gcc (GCC) 8.0.1 20180324 (Red Hat 8.0.1-0.20) >> >> The file that causes the error is tools/lib/bpf/libbpf.c >> >> Here is the error message: >> >> [root@p23lp27] # make V=1 EXTRA_CFLAGS="-Wp,-D_FORTIFY_SOURCE=2 -O2" >> [...] >> Makefile.config:849: No openjdk development package found, please >> install JDK package, e.g. openjdk-8-jdk, java-1.8.0-openjdk-devel >> Warning: Kernel ABI header at 'tools/include/uapi/linux/if_link.h' >> differs from latest version at 'include/uapi/linux/if_link.h' >> CC libbpf.o >> libbpf.c: In function ‘bpf_perf_event_read_simple’: >> libbpf.c:2342:6: error: ‘ret’ may be used uninitialized in this >> function [-Werror=maybe-uninitialized] >> int ret; >> ^ >> cc1: all warnings being treated as errors >> mv: cannot stat './.libbpf.o.tmp': No such file or directory >> /home6/tmricht/linux-next/tools/build/Makefile.build:96: recipe for target 'libbpf.o' failed >> >> Fix this warning and add an addition check at the beginning >> of the while loop. >> >> Cc: Alexei Starovoitov >> Cc: Daniel Borkmann >> >> Suggested-by: Jakub Kicinski >> Signed-off-by: Thomas Richter > > Ah, you already sent this, LGTM, thanks Thomas! > >> tools/lib/bpf/libbpf.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c >> index 73465caa33ba..66965ca96113 100644 >> --- a/tools/lib/bpf/libbpf.c >> +++ b/tools/lib/bpf/libbpf.c >> @@ -2349,6 +2349,8 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, >> >> begin = base + data_tail % size; >> end = base + data_head % size; >> + if (begin == end) >> + return LIBBPF_PERF_EVENT_ERROR; >> >> while (begin != end) { >> struct perf_event_header *ehdr; One question though, any objections to go for something like the below instead? I doubt we ever hit this in a 'normal' situation, and given we already test for the begin and end anyway, we could just avoid the extra test altogether. I could change it to the below if you're good as well (no need to resend anything): diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index d881d37..1aafdbe 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -2273,8 +2273,8 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, volatile struct perf_event_mmap_page *header = mem; __u64 data_tail = header->data_tail; __u64 data_head = header->data_head; + int ret = LIBBPF_PERF_EVENT_ERROR; void *base, *begin, *end; - int ret; asm volatile("" ::: "memory"); /* in real code it should be smp_rmb() */ if (data_head == data_tail) Thanks, Daniel