Re: [dpdk-dev] [PATCH] vhost: fix false-positive warning from clang5

[Thomas Monjalon <thomas@monjalon.net>]

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:
> > 
> > ../lib/librte_vhost/iotlb.c:318:6: warning: variable 'socket' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> > 
> > 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.
> > 
> > However, this is not immediately obvious, and is perhaps a little fragile,
> > 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.
> > 
> > Fixes: d012d1f293f4 ("vhost: add IOTLB helper functions")
> > 
> > CC: Maxime Coquelin <maxime.coquelin@redhat.com>
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> >   lib/librte_vhost/iotlb.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> 
> I agree this is a bit fragile. Thanks for handling this:
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

New error with this patch:

lib/librte_vhost/iotlb.c:303:6: error:
unused variable ‘ret’ [-Werror=unused-variable]