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Fri, 02 Oct 2020 06:59:49 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 7d83799f-3cc9-44c5-b044-c9f711ab4f01; Fri, 02 Oct 2020 06:59:48 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 920A6AF68; Fri, 2 Oct 2020 06:59:47 +0000 (UTC) Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kOF2j-0007i5-Fn for xen-devel@lists.xenproject.org; Fri, 02 Oct 2020 06:59:49 +0000 X-Inumbo-ID: 7d83799f-3cc9-44c5-b044-c9f711ab4f01 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 7d83799f-3cc9-44c5-b044-c9f711ab4f01; Fri, 02 Oct 2020 06:59:48 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1601621987; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=N+s+Wwos+DreJlRD4jiPthFzPNCYs2RfABt2kX87T/U=; b=BEi4wBE4ORF3UMywez9Dy9b2W18GxnWmQCZIZwbUdyJw04OQuqGLsp0+wBV34bJt36fx3H wLUXF5skJQsJNjho5smmVGKQunwdSQD7qpLfuGdhzhefBsd6r9Z209qZBhYAQEJEj19QL9 jymxRT3eEEziUUeLVT2dgSH4nN9s0i8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 920A6AF68; Fri, 2 Oct 2020 06:59:47 +0000 (UTC) Subject: Re: [PATCH v3] tools/libs/stat: fix broken build To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Cc: Bertrand Marquis , "open list:X86" , Ian Jackson , Wei Liu References: <20200912130836.11024-1-jgross@suse.com> <5232FD74-9636-4EF4-81F8-2EF7EE21D326@arm.com> <87CA2B55-B372-458C-82CC-2423B8AC3EEE@arm.com> <8ddad01e-cf1a-7752-1371-a505fb26dc47@suse.com> From: Jan Beulich Message-ID: <90a39759-63c1-28b9-f112-d8b3cc083565@suse.com> Date: Fri, 2 Oct 2020 08:59:50 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <8ddad01e-cf1a-7752-1371-a505fb26dc47@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 02.10.2020 08:51, Jürgen Groß wrote: > On 02.10.20 08:20, Jan Beulich wrote: >> On 02.10.2020 06:50, Jürgen Groß wrote: >>> On 01.10.20 18:38, Bertrand Marquis wrote: >>>> Hi Juergen, >>>> >>>>> On 14 Sep 2020, at 11:58, Bertrand Marquis wrote: >>>>> >>>>> >>>>> >>>>>> On 12 Sep 2020, at 14:08, Juergen Gross wrote: >>>>>> >>>>>> Making getBridge() static triggered a build error with some gcc versions: >>>>>> >>>>>> error: 'strncpy' output may be truncated copying 15 bytes from a string of >>>>>> length 255 [-Werror=stringop-truncation] >>>>>> >>>>>> Fix that by using a buffer with 256 bytes instead. >>>>>> >>>>>> Fixes: 6d0ec053907794 ("tools: split libxenstat into new tools/libs/stat directory") >>>>>> Signed-off-by: Juergen Gross >>>>> Reviewed-by: Bertrand Marquis >>>> >>>> Sorry i have to come back on this one. >>>> >>>> I still see an error compiling with Yocto on this one: >>>> | inlined from 'xenstat_collect_networks' at xenstat_linux.c:306:2: >>>> | xenstat_linux.c:81:6: error: 'strncpy' output may be truncated copying 255 bytes from a string of length 255 [-Werror=stringop-truncation] >>>> | 81 | strncpy(result, de->d_name, resultLen); >>>> | | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>>> >>>> To solve it, I need to define devBridge[257] as devNoBrideg. >>> >>> IMHO this is a real compiler error. >>> >>> de->d_name is an array of 256 bytes, so doing strncpy() from that to >>> another array of 256 bytes with a length of 256 won't truncate anything. >> >> That's a matter of how you look at it, I think: If the original array >> doesn't hold a nul-terminated string, the destination array won't >> either, yet the common goal of strncpy() is to yield a properly nul- >> terminated string. IOW the warning may be since the standard even has >> a specific foot note to point out this possible pitfall. > > If the source doesn't hold a nul-terminated string there will still be > 256 bytes copied, so there is no truncation done during strncpy(). > > In fact there is no way to use strncpy() in a safe way on a fixed sized > source array with the above semantics: either the target is larger than > the source and length is at least sizeof(source) + 1, resulting in a > possible read beyond the end of source, or the target is the same length > leading to the error. I agree with all of what you say, but I can also see why said foot note alone may have motivated the emission of the warning. Jan