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bh=aD2Vx2/uz+3g7nz0MpaN9DRRw/XZwG/tkyCwW3QkdhI=; b=awtsa13ukuGyVcxrG8IjgP0j1dIYIrUMTy3Y22A2eequkGR24sd+mvGs2Mu482Cb9wVtBi nkUTgYJfJtxaA+9xGLC/T7KLaUO3/t1zSLbUDP+ZkwJVRAaJ7D0mqU3QMrLSnSvqFThzQj /YAFPZssPkcfc4RUn/SPIOitRlyjN6w= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-210-DQnj7Ac0MEWKWbLs2ozLlQ-1; Thu, 22 Apr 2021 06:15:26 -0400 X-MC-Unique: DQnj7Ac0MEWKWbLs2ozLlQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B726018982B8; Thu, 22 Apr 2021 10:15:25 +0000 (UTC) Received: from redhat.com (ovpn-112-200.ams2.redhat.com [10.36.112.200]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D2F9D5C1B4; Thu, 22 Apr 2021 10:15:22 +0000 (UTC) Date: Thu, 22 Apr 2021 11:15:19 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Subject: Re: s390-ccw: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=] Message-ID: References: <4e327c80-8f5d-c848-b524-7f2c75255da4@redhat.com> <485773db-fca2-03ca-c6e8-90ef313fb8f1@redhat.com> MIME-Version: 1.0 In-Reply-To: <485773db-fca2-03ca-c6e8-90ef313fb8f1@redhat.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Janosch Frank , Cornelia Huck , Richard Henderson , qemu-devel , Christian Borntraeger , qemu-s390x , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 22, 2021 at 06:47:30AM +0200, Thomas Huth wrote: > On 22/04/2021 06.18, Philippe Mathieu-Daudé wrote: > > Hi Thomas, Daniel, Stefano, > > > > Regarding the following warning (GCC 11 on Fedora 34): > > > > In file included from pc-bios/s390-ccw/main.c:11: > > > > In function ‘memset’, > > > > inlined from ‘boot_setup’ at pc-bios/s390-ccw/main.c:185:5, > > > > inlined from ‘main’ at pc-bios/s390-ccw/main.c:288:5: > > > > pc-bios/s390-ccw/libc.h:28:14: warning: writing 1 byte into a region of > > size 0 [-Wstringop-overflow=] > > > > 28 | p[i] = c; > > > > | ~~~~~^~~ > > > > Daniel were right on IRC: > > > > danpb: it is from a call memset((char *)S390EP, 0, 6) where S390EP > > is just a constant address 0x10008 > > danpb: the compiler doesn't now how big that is, so it seems to assume > > it is zero length > > > > This is a known GCC issue: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578 > > "gcc-11 -Warray-bounds or -Wstringop-overread warning when accessing a > > pointer from integer literal" > > Hi Philippe, > > thanks for following up with the gcc bugzilla! > > ... so the problem is that GCC thinks we're in fact dereferencing a NULL > pointer at offset 0x10008 here? Wow, that's ... crazy. > > Not sure what to do now - wait for the bug to get resolved? Compile the > s390-ccw bios with -Wno-stringop-overread ? Add "volatiles" here and there > to hope that these silence the compiler warnings? ... I tend to wait for the > bug ticket to see whether the GCC folks change the behavior of the compiler > again, but I'm open for other suggestions. Assuming it is just this one place in the code ,then we should just use "pragma" to temporarily disable/re-enable that single warning flag either side of the problem. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|