From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46551) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gZK8y-0003nv-HR for qemu-devel@nongnu.org; Tue, 18 Dec 2018 13:31:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gZK8w-0001Hi-NS for qemu-devel@nongnu.org; Tue, 18 Dec 2018 13:31:00 -0500 References: <20181218175122.3229-1-philmd@redhat.com> <20181218175122.3229-3-philmd@redhat.com> From: Eric Blake Message-ID: Date: Tue, 18 Dec 2018 12:30:02 -0600 MIME-Version: 1.0 In-Reply-To: <20181218175122.3229-3-philmd@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v3 2/5] block/sheepdog: Use QEMU_NONSTRING for non NUL-terminated arrays List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org Cc: "Michael S. Tsirkin" , Juan Quintela , qemu-block@nongnu.org, 1803872@bugs.launchpad.net, =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , =?UTF-8?Q?C=c3=a9dric_Le_Goater?= , "Dr. David Alan Gilbert" , Howard Spoelstra , Jeff Cody , David Hildenbrand , Paolo Bonzini , Stefan Weil , Markus Armbruster , Kevin Wolf , Ben Pye , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , Thomas Huth , Igor Mammedov , Liu Yuan , David Gibson , Max Reitz On 12/18/18 11:51 AM, Philippe Mathieu-Daud=C3=A9 wrote: > GCC 8 added a -Wstringop-truncation warning: >=20 > The -Wstringop-truncation warning added in GCC 8.0 via r254630 for > bug 81117 is specifically intended to highlight likely unintended > uses of the strncpy function that truncate the terminating NUL > character from the source string. >=20 > This new warning leads to compilation failures: >=20 > CC block/sheepdog.o > qemu/block/sheepdog.c: In function 'find_vdi_name': > qemu/block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 e= quals destination size [-Werror=3Dstringop-truncation] > strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN); > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > make: *** [qemu/rules.mak:69: block/sheepdog.o] Error 1 >=20 > As described previous to the strncpy() calls, the use of strncpy() is > correct here: >=20 > /* This pair of strncpy calls ensures that the buffer is zero-fill= ed, > * which is desirable since we'll soon be sending those bytes, and > * don't want the send_req to read uninitialized data. > */ > strncpy(buf, filename, SD_MAX_VDI_LEN); > strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN); >=20 > Use the QEMU_NONSTRING attribute, since this array is intended to store > character arrays that do not necessarily contain a terminating NUL. >=20 > Suggested-by: Michael S. Tsirkin > Signed-off-by: Philippe Mathieu-Daud=C3=A9 > --- > block/sheepdog.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Reviewed-by: Eric Blake >=20 > diff --git a/block/sheepdog.c b/block/sheepdog.c > index 0125df9d49..d4ad6b119d 100644 > --- a/block/sheepdog.c > +++ b/block/sheepdog.c > @@ -1224,7 +1224,7 @@ static int find_vdi_name(BDRVSheepdogState *s, co= nst char *filename, > SheepdogVdiReq hdr; > SheepdogVdiRsp *rsp =3D (SheepdogVdiRsp *)&hdr; > unsigned int wlen, rlen =3D 0; > - char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN]; > + QEMU_NONSTRING char buf[SD_MAX_VDI_LEN + SD_MAX_VDI_TAG_LEN]; > =20 > fd =3D connect_to_sdog(s, errp); > if (fd < 0) { >=20 --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org