From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Monjalon Subject: Re: [PATCH] vhost: fix false-positive warning from clang5 Date: Wed, 11 Oct 2017 12:51:59 +0200 Message-ID: <8881744.fh4vGQZOj9@xps> References: <20171011095907.229893-1-bruce.richardson@intel.com> <0a77b5a9-fa1a-6409-2518-5e2738888da9@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: dev@dpdk.org, Maxime Coquelin , yliu@fridaylinux.org To: Bruce Richardson Return-path: Received: from out1-smtp.messagingengine.com (out1-smtp.messagingengine.com [66.111.4.25]) by dpdk.org (Postfix) with ESMTP id D330F2B9A for ; Wed, 11 Oct 2017 12:52:00 +0200 (CEST) In-Reply-To: <0a77b5a9-fa1a-6409-2518-5e2738888da9@redhat.com> List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" 11/10/2017 12:12, Maxime Coquelin: > On 10/11/2017 11:59 AM, Bruce Richardson wrote: > > When compiling with clang extra warning flags, such as used by default = with > > meson, a warning is given in iotlb.c: > >=20 > > ../lib/librte_vhost/iotlb.c:318:6: warning: variable 'socket' is used u= ninitialized whenever 'if' condition is false [-Wsometimes-uninitialized] > >=20 > > This is a false positive, as the socket value will be initialized by the > > call to get_mempolicy in the case where the NUMA build-time flag is set, > > and in cases where it is not set, "if (ret)" will always be true as ret= is > > initialized to -1 and never changed. > >=20 > > However, this is not immediately obvious, and is perhaps a little fragi= le, > > as it will break if other code using ret is subsequently added above the > > call to get_mempolicy by someone unaware of this subtle dependency. > > Therefore, we can fix the warning and making the code more robust by > > explicitly initializing socket to zero, and moving the extra condition > > check on ret into the #ifdef alongside the call to get_mempolicy which = sets > > ret. > >=20 > > Fixes: d012d1f293f4 ("vhost: add IOTLB helper functions") > >=20 > > CC: Maxime Coquelin > > Signed-off-by: Bruce Richardson > > --- > > lib/librte_vhost/iotlb.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > >=20 >=20 > I agree this is a bit fragile. Thanks for handling this: > Reviewed-by: Maxime Coquelin New error with this patch: lib/librte_vhost/iotlb.c:303:6: error: unused variable =E2=80=98ret=E2=80=99 [-Werror=3Dunused-variable]