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=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 28515C4742C for ; Thu, 12 Nov 2020 01:45:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCE5A2076E for ; Thu, 12 Nov 2020 01:45:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728761AbgKLBei convert rfc822-to-8bit (ORCPT ); Wed, 11 Nov 2020 20:34:38 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:31904 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727706AbgKKXDz (ORCPT ); Wed, 11 Nov 2020 18:03:55 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-89-Hjz3Y7RkMHS23JXaSvpHwQ-1; Wed, 11 Nov 2020 23:03:48 +0000 X-MC-Unique: Hjz3Y7RkMHS23JXaSvpHwQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Wed, 11 Nov 2020 23:03:47 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Wed, 11 Nov 2020 23:03:47 +0000 From: David Laight To: 'Dave Martin' , Arnaldo Carvalho de Melo CC: Andre Przywara , "leo.yan@linaro.org" , James Clark , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , "Namhyung Kim" , Al Grant , Wei Li , John Garry , Will Deacon , Mathieu Poirier , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH v8 06/22] perf arm-spe: Refactor printing string to buffer Thread-Topic: [PATCH v8 06/22] perf arm-spe: Refactor printing string to buffer Thread-Index: AQHWuFRInoKVOHB17kCDuu646O3VGqnDiy6g Date: Wed, 11 Nov 2020 23:03:47 +0000 Message-ID: <3dc873b262bd4659a2c6ae935d69c8fc@AcuMS.aculab.com> References: <20201111071149.815-1-leo.yan@linaro.org> <20201111071149.815-7-leo.yan@linaro.org> <20201111153555.GG355344@kernel.org> <20201111173922.GA380127@kernel.org> <20201111175827.GR6882@arm.com> In-Reply-To: <20201111175827.GR6882@arm.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Martin > Sent: 11 November 2020 17:58 > > On Wed, Nov 11, 2020 at 05:39:22PM +0000, Arnaldo Carvalho de Melo wrote: > > Em Wed, Nov 11, 2020 at 03:45:23PM +0000, Andr� Przywara escreveu: > > > On 11/11/2020 15:35, Arnaldo Carvalho de Melo wrote: > > > > > > Hi Arnaldo, > > > > > > thanks for taking a look! > > > > > > > Em Wed, Nov 11, 2020 at 03:11:33PM +0800, Leo Yan escreveu: > > > >> When outputs strings to the decoding buffer with function snprintf(), > > > >> SPE decoder needs to detects if any error returns from snprintf() and if > > > >> so needs to directly bail out. If snprintf() returns success, it needs > > > >> to update buffer pointer and reduce the buffer length so can continue to > > > >> output the next string into the consequent memory space. > > > >> > > > >> This complex logics are spreading in the function arm_spe_pkt_desc() so > > > >> there has many duplicate codes for handling error detecting, increment > > > >> buffer pointer and decrement buffer size. > > > >> > > > >> To avoid the duplicate code, this patch introduces a new helper function > > > >> arm_spe_pkt_snprintf() which is used to wrap up the complex logics, and > > > >> it's used by the caller arm_spe_pkt_desc(). > > > >> > > > >> This patch also moves the variable 'blen' as the function's local > > > >> variable, this allows to remove the unnecessary braces and improve the > > > >> readability. > > > >> > > > >> Suggested-by: Dave Martin > > > >> Signed-off-by: Leo Yan > > > >> Reviewed-by: Andre Przywara > > > >> --- > > > >> .../arm-spe-decoder/arm-spe-pkt-decoder.c | 260 +++++++++--------- > > > >> 1 file changed, 126 insertions(+), 134 deletions(-) > > > >> > > > >> diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c b/tools/perf/util/arm-spe- > decoder/arm-spe-pkt-decoder.c > > > >> index 04fd7fd7c15f..1970686f7020 100644 > > > >> --- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c > > > >> +++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c > > > >> @@ -9,6 +9,7 @@ > > > >> #include > > > >> #include > > > >> #include > > > >> +#include > > > >> > > > >> #include "arm-spe-pkt-decoder.h" > > > >> > > > >> @@ -258,192 +259,183 @@ int arm_spe_get_packet(const unsigned char *buf, size_t len, > > > >> return ret; > > > >> } > > > >> > > > >> +static int arm_spe_pkt_snprintf(int *err, char **buf_p, size_t *blen, > > > >> + const char *fmt, ...) > > > >> +{ > > > >> + va_list ap; > > > >> + int ret; > > > >> + > > > >> + /* Bail out if any error occurred */ > > > >> + if (err && *err) > > > >> + return *err; > > > >> + > > > >> + va_start(ap, fmt); > > > >> + ret = vsnprintf(*buf_p, *blen, fmt, ap); > > > >> + va_end(ap); > > > >> + > > > >> + if (ret < 0) { > > > >> + if (err && !*err) > > > >> + *err = ret; > > > >> + > > > >> + /* > > > >> + * A return value of (*blen - 1) or more means that the > > > >> + * output was truncated and the buffer is overrun. > > > >> + */ > > > >> + } else if (ret >= ((int)*blen - 1)) { > > > >> + (*buf_p)[*blen - 1] = '\0'; > > > >> + > > > >> + /* > > > >> + * Set *err to 'ret' to avoid overflow if tries to > > > >> + * fill this buffer sequentially. > > > >> + */ > > > >> + if (err && !*err) > > > >> + *err = ret; > > > >> + } else { > > > >> + *buf_p += ret; > > > >> + *blen -= ret; > > > >> + } > > > >> + > > > >> + return ret; > > > >> +} > > > >> + I'm not entirely sure that snprintf() can actually return a negative value. Every implementation (except the microsoft one) also always writes a '\0' even when the buffer is too short. A simple wrapper that lets you append output and detect overflow is: ret = vsnprintf(buf, len, ...); if (ret < 0) /* just in case */ return 0; return ret > len ? len : ret; So on overflow the sum of the lengths is equal to the buffer size (ie includes the terminating '\0'. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)