gcc -L/usr/lib -Wl,-R/usr/lib -L/usr/pkg/lib -Wl,-R/usr/pkg/lib
  -pthread -o blktapctrl blktapctrl.o blktapctrl_netbsd.o
  /WRKOBJDIR/sysutils/xentools42/work/
  xen-4.2.5/tools/blktap/drivers/../../../tools/libxc/libxenctrl.so

/WRKOBJDIR/sysutils/xentools42/work/ 
  xen-4.2.5/tools/blktap/drivers/../../../tools/xenstore/libxenstore.so
  -L../lib -lblktap -lrt -lm block-qcow.c: In function
  'get_cluster_offset':

block-qcow.c:619:7: error: 'tmp_ptr2' may be used uninitialized in
this function [-Werror=maybe-uninitialized]

   if (write(s->fd, tmp_ptr2, 4096) != 4096) { 
                    ^ block-qcow.c:399:12:
        error: 'tmp_ptr' may be used uninitialized in this function
       [-Werror=maybe-uninitialized]

  uint64_t *tmp_ptr;
            ^
cc1: all warnings being treated as errors

/WRKOBJDIR/sysutils/xentools42/work/xen-4.2.5/tools/blktap/drivers/../../../tools/Rules.mk:93:
recipe for target 'block-qcow.o' failed

gmake[4]: *** [block-qcow.o] Error 1