diff mbox series

[1/9] golang/xenlight: Don't try to marshall zero-length arrays

Message ID 20191227163224.4113837-1-george.dunlap@citrix.com (mailing list archive)
State New, archived
Headers show
Series [1/9] golang/xenlight: Don't try to marshall zero-length arrays | expand

Commit Message

George Dunlap Dec. 27, 2019, 4:32 p.m. UTC 
The current fromC array code will do the "magic" casting and
martialling even when num_foo variable is 0.  Go crashes when doing
the cast.

Furthermore, the current toC array code will convert a nil slice into
a zero-length malloc.  The resulting pointer is non-NULL, and confuses
libxl.

Only do array marshalling if the number of elements is non-zero;
otherwise, leave the target pointer empty (nil for Go slices, NULL for
C arrays).

The toC half of this should be folded into "golang/xenlight:
implement array Go to C marshaling".

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
---
CC: Nick Rosbrook <rosbrookn@ainfosec.com>
---
 tools/golang/xenlight/gengotypes.py  |   13 +-
 tools/golang/xenlight/helpers.gen.go | 1232 ++++++++++++++------------
 2 files changed, 671 insertions(+), 574 deletions(-)

Comments

George Dunlap Dec. 27, 2019, 4:36 p.m. UTC | #1 
On 12/27/19 4:32 PM, George Dunlap wrote:
> The current fromC array code will do the "magic" casting and
> martialling even when num_foo variable is 0.  Go crashes when doing
> the cast.
> 
> Furthermore, the current toC array code will convert a nil slice into
> a zero-length malloc.  The resulting pointer is non-NULL, and confuses
> libxl.
> 
> Only do array marshalling if the number of elements is non-zero;
> otherwise, leave the target pointer empty (nil for Go slices, NULL for
> C arrays).
> 
> The toC half of this should be folded into "golang/xenlight:
> implement array Go to C marshaling".
> 
> Signed-off-by: George Dunlap <george.dunlap@citrix.com>

The .go program I used to test this series is attached, to give you an
idea what the current iteration looks like, and potentially give it a spin.

 -George
Nick Rosbrook Jan. 4, 2020, 5:11 p.m. UTC | #2 
> The current fromC array code will do the "magic" casting and
> martialling even when num_foo variable is 0.  Go crashes when doing
> the cast.
>
> Furthermore, the current toC array code will convert a nil slice into
> a zero-length malloc.  The resulting pointer is non-NULL, and confuses
> libxl.
>
> Only do array marshalling if the number of elements is non-zero;
> otherwise, leave the target pointer empty (nil for Go slices, NULL for
> C arrays).
>
> The toC half of this should be folded into "golang/xenlight:
> implement array Go to C marshaling".

Looks good to me. I will make the toC change when I send v5 of my series.

-NR
diff mbox series

Patch

diff --git a/tools/golang/xenlight/gengotypes.py b/tools/golang/xenlight/gengotypes.py
index a972754d36..5363ca062d 100644
--- a/tools/golang/xenlight/gengotypes.py
+++ b/tools/golang/xenlight/gengotypes.py
@@ -419,7 +419,8 @@  def xenlight_golang_array_from_C(ty = None):
     clenvar    = ty.type.lenvar.name
     golenvar   = xenlight_golang_fmt_name(clenvar,exported=False)
 
-    s += '{} := int(xc.{})\n'.format(golenvar, clenvar)
+    s += 'x.{} = nil\n'.format(goname)
+    s += 'if {} := int(xc.{}); {} > 0 {{\n'.format(golenvar, clenvar, golenvar)
     s += '{} := '.format(cslice)
     s +='(*[1<<28]C.{})(unsafe.Pointer(xc.{}))[:{}:{}]\n'.format(ctypename, cname,
                                                                 golenvar, golenvar)
@@ -433,7 +434,7 @@  def xenlight_golang_array_from_C(ty = None):
         s += 'if err := x.{}[i].fromC(&v); err != nil {{\n'.format(goname)
         s += 'return err }\n'
 
-    s += '}\n'
+    s += '}\n}\n'
 
     return s
 
@@ -599,7 +600,7 @@  def xenlight_golang_array_to_C(ty = None, dispose_fn = ''):
 
     is_enum = isinstance(ty.type.elem_type,idl.Enumeration)
     if gotypename in go_builtin_types or is_enum:
-        s += '{} := len(x.{})\n'.format(golenvar,goname)
+        s += 'if {} := len(x.{}); {} > 0 {{\n'.format(golenvar,goname, golenvar)
         s += 'xc.{} = (*C.{})(C.malloc(C.size_t({}*{})))\n'.format(cname,ctypename,
                                                                    golenvar,golenvar)
         s += 'xc.{} = C.int({})\n'.format(clenvar,golenvar)
@@ -608,11 +609,11 @@  def xenlight_golang_array_to_C(ty = None, dispose_fn = ''):
                                                                       golenvar,golenvar)
         s += 'for i,v := range x.{} {{\n'.format(goname)
         s += 'c{}[i] = C.{}(v)\n'.format(goname,ctypename)
-        s += '}\n'
+        s += '}\n}\n'
 
         return s
 
-    s += '{} := len(x.{})\n'.format(golenvar,goname)
+    s += 'if {} := len(x.{}); {} > 0 {{\n'.format(golenvar,goname, golenvar)
     s += 'xc.{} = (*C.{})(C.malloc(C.ulong({})*C.sizeof_{}))\n'.format(cname,ctypename,
                                                                    golenvar,ctypename)
     s += 'xc.{} = C.int({})\n'.format(clenvar,golenvar)
@@ -625,7 +626,7 @@  def xenlight_golang_array_to_C(ty = None, dispose_fn = ''):
     s += 'C.{}(&xc)\n'.format(dispose_fn)
     s += 'return xc,err\n}\n'
     s += 'c{}[i] = tmp\n'.format(goname)
-    s += '}\n'
+    s += '}\n}\n'
 
     return s
 
diff --git a/tools/golang/xenlight/helpers.gen.go b/tools/golang/xenlight/helpers.gen.go
index 3e588dd1c2..61cd73595e 100644
--- a/tools/golang/xenlight/helpers.gen.go
+++ b/tools/golang/xenlight/helpers.gen.go
@@ -528,12 +528,14 @@  func (x *SchedParams) toC() (xc C.libxl_sched_params, err error) {
 
 func (x *VcpuSchedParams) fromC(xc *C.libxl_vcpu_sched_params) error {
 	x.Sched = Scheduler(xc.sched)
-	numVcpus := int(xc.num_vcpus)
-	cVcpus := (*[1 << 28]C.libxl_sched_params)(unsafe.Pointer(xc.vcpus))[:numVcpus:numVcpus]
-	x.Vcpus = make([]SchedParams, numVcpus)
-	for i, v := range cVcpus {
-		if err := x.Vcpus[i].fromC(&v); err != nil {
-			return err
+	x.Vcpus = nil
+	if numVcpus := int(xc.num_vcpus); numVcpus > 0 {
+		cVcpus := (*[1 << 28]C.libxl_sched_params)(unsafe.Pointer(xc.vcpus))[:numVcpus:numVcpus]
+		x.Vcpus = make([]SchedParams, numVcpus)
+		for i, v := range cVcpus {
+			if err := x.Vcpus[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -543,17 +545,18 @@  func (x *VcpuSchedParams) fromC(xc *C.libxl_vcpu_sched_params) error {
 func (x *VcpuSchedParams) toC() (xc C.libxl_vcpu_sched_params, err error) {
 	C.libxl_vcpu_sched_params_init(&xc)
 	xc.sched = C.libxl_scheduler(x.Sched)
-	numVcpus := len(x.Vcpus)
-	xc.vcpus = (*C.libxl_sched_params)(C.malloc(C.ulong(numVcpus) * C.sizeof_libxl_sched_params))
-	xc.num_vcpus = C.int(numVcpus)
-	cVcpus := (*[1 << 28]C.libxl_sched_params)(unsafe.Pointer(xc.vcpus))[:numVcpus:numVcpus]
-	for i, v := range x.Vcpus {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_vcpu_sched_params_dispose(&xc)
-			return xc, err
+	if numVcpus := len(x.Vcpus); numVcpus > 0 {
+		xc.vcpus = (*C.libxl_sched_params)(C.malloc(C.ulong(numVcpus) * C.sizeof_libxl_sched_params))
+		xc.num_vcpus = C.int(numVcpus)
+		cVcpus := (*[1 << 28]C.libxl_sched_params)(unsafe.Pointer(xc.vcpus))[:numVcpus:numVcpus]
+		for i, v := range x.Vcpus {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_vcpu_sched_params_dispose(&xc)
+				return xc, err
+			}
+			cVcpus[i] = tmp
 		}
-		cVcpus[i] = tmp
 	}
 	return xc, nil
 }
@@ -586,11 +589,13 @@  func (x *DomainSchedParams) toC() (xc C.libxl_domain_sched_params, err error) {
 
 func (x *VnodeInfo) fromC(xc *C.libxl_vnode_info) error {
 	x.Memkb = uint64(xc.memkb)
-	numDistances := int(xc.num_distances)
-	cDistances := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.distances))[:numDistances:numDistances]
-	x.Distances = make([]uint32, numDistances)
-	for i, v := range cDistances {
-		x.Distances[i] = uint32(v)
+	x.Distances = nil
+	if numDistances := int(xc.num_distances); numDistances > 0 {
+		cDistances := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.distances))[:numDistances:numDistances]
+		x.Distances = make([]uint32, numDistances)
+		for i, v := range cDistances {
+			x.Distances[i] = uint32(v)
+		}
 	}
 	x.Pnode = uint32(xc.pnode)
 	if err := x.Vcpus.fromC(&xc.vcpus); err != nil {
@@ -603,12 +608,13 @@  func (x *VnodeInfo) fromC(xc *C.libxl_vnode_info) error {
 func (x *VnodeInfo) toC() (xc C.libxl_vnode_info, err error) {
 	C.libxl_vnode_info_init(&xc)
 	xc.memkb = C.uint64_t(x.Memkb)
-	numDistances := len(x.Distances)
-	xc.distances = (*C.uint32_t)(C.malloc(C.size_t(numDistances * numDistances)))
-	xc.num_distances = C.int(numDistances)
-	cDistances := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.distances))[:numDistances:numDistances]
-	for i, v := range x.Distances {
-		cDistances[i] = C.uint32_t(v)
+	if numDistances := len(x.Distances); numDistances > 0 {
+		xc.distances = (*C.uint32_t)(C.malloc(C.size_t(numDistances * numDistances)))
+		xc.num_distances = C.int(numDistances)
+		cDistances := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.distances))[:numDistances:numDistances]
+		for i, v := range x.Distances {
+			cDistances[i] = C.uint32_t(v)
+		}
 	}
 	xc.pnode = C.uint32_t(x.Pnode)
 	xc.vcpus, err = x.Vcpus.toC()
@@ -644,20 +650,24 @@  func (x *DomainBuildInfo) fromC(xc *C.libxl_domain_build_info) error {
 	if err := x.Nodemap.fromC(&xc.nodemap); err != nil {
 		return err
 	}
-	numVcpuHardAffinity := int(xc.num_vcpu_hard_affinity)
-	cVcpuHardAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_hard_affinity))[:numVcpuHardAffinity:numVcpuHardAffinity]
-	x.VcpuHardAffinity = make([]Bitmap, numVcpuHardAffinity)
-	for i, v := range cVcpuHardAffinity {
-		if err := x.VcpuHardAffinity[i].fromC(&v); err != nil {
-			return err
+	x.VcpuHardAffinity = nil
+	if numVcpuHardAffinity := int(xc.num_vcpu_hard_affinity); numVcpuHardAffinity > 0 {
+		cVcpuHardAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_hard_affinity))[:numVcpuHardAffinity:numVcpuHardAffinity]
+		x.VcpuHardAffinity = make([]Bitmap, numVcpuHardAffinity)
+		for i, v := range cVcpuHardAffinity {
+			if err := x.VcpuHardAffinity[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
-	numVcpuSoftAffinity := int(xc.num_vcpu_soft_affinity)
-	cVcpuSoftAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_soft_affinity))[:numVcpuSoftAffinity:numVcpuSoftAffinity]
-	x.VcpuSoftAffinity = make([]Bitmap, numVcpuSoftAffinity)
-	for i, v := range cVcpuSoftAffinity {
-		if err := x.VcpuSoftAffinity[i].fromC(&v); err != nil {
-			return err
+	x.VcpuSoftAffinity = nil
+	if numVcpuSoftAffinity := int(xc.num_vcpu_soft_affinity); numVcpuSoftAffinity > 0 {
+		cVcpuSoftAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_soft_affinity))[:numVcpuSoftAffinity:numVcpuSoftAffinity]
+		x.VcpuSoftAffinity = make([]Bitmap, numVcpuSoftAffinity)
+		for i, v := range cVcpuSoftAffinity {
+			if err := x.VcpuSoftAffinity[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 	if err := x.NumaPlacement.fromC(&xc.numa_placement); err != nil {
@@ -682,12 +692,14 @@  func (x *DomainBuildInfo) fromC(xc *C.libxl_domain_build_info) error {
 		return err
 	}
 	x.BlkdevStart = C.GoString(xc.blkdev_start)
-	numVnumaNodes := int(xc.num_vnuma_nodes)
-	cVnumaNodes := (*[1 << 28]C.libxl_vnode_info)(unsafe.Pointer(xc.vnuma_nodes))[:numVnumaNodes:numVnumaNodes]
-	x.VnumaNodes = make([]VnodeInfo, numVnumaNodes)
-	for i, v := range cVnumaNodes {
-		if err := x.VnumaNodes[i].fromC(&v); err != nil {
-			return err
+	x.VnumaNodes = nil
+	if numVnumaNodes := int(xc.num_vnuma_nodes); numVnumaNodes > 0 {
+		cVnumaNodes := (*[1 << 28]C.libxl_vnode_info)(unsafe.Pointer(xc.vnuma_nodes))[:numVnumaNodes:numVnumaNodes]
+		x.VnumaNodes = make([]VnodeInfo, numVnumaNodes)
+		for i, v := range cVnumaNodes {
+			if err := x.VnumaNodes[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 	x.MaxGrantFrames = uint32(xc.max_grant_frames)
@@ -712,26 +724,32 @@  func (x *DomainBuildInfo) fromC(xc *C.libxl_domain_build_info) error {
 	if err := x.SchedParams.fromC(&xc.sched_params); err != nil {
 		return err
 	}
-	numIoports := int(xc.num_ioports)
-	cIoports := (*[1 << 28]C.libxl_ioport_range)(unsafe.Pointer(xc.ioports))[:numIoports:numIoports]
-	x.Ioports = make([]IoportRange, numIoports)
-	for i, v := range cIoports {
-		if err := x.Ioports[i].fromC(&v); err != nil {
-			return err
+	x.Ioports = nil
+	if numIoports := int(xc.num_ioports); numIoports > 0 {
+		cIoports := (*[1 << 28]C.libxl_ioport_range)(unsafe.Pointer(xc.ioports))[:numIoports:numIoports]
+		x.Ioports = make([]IoportRange, numIoports)
+		for i, v := range cIoports {
+			if err := x.Ioports[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
-	numIrqs := int(xc.num_irqs)
-	cIrqs := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.irqs))[:numIrqs:numIrqs]
-	x.Irqs = make([]uint32, numIrqs)
-	for i, v := range cIrqs {
-		x.Irqs[i] = uint32(v)
+	x.Irqs = nil
+	if numIrqs := int(xc.num_irqs); numIrqs > 0 {
+		cIrqs := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.irqs))[:numIrqs:numIrqs]
+		x.Irqs = make([]uint32, numIrqs)
+		for i, v := range cIrqs {
+			x.Irqs[i] = uint32(v)
+		}
 	}
-	numIomem := int(xc.num_iomem)
-	cIomem := (*[1 << 28]C.libxl_iomem_range)(unsafe.Pointer(xc.iomem))[:numIomem:numIomem]
-	x.Iomem = make([]IomemRange, numIomem)
-	for i, v := range cIomem {
-		if err := x.Iomem[i].fromC(&v); err != nil {
-			return err
+	x.Iomem = nil
+	if numIomem := int(xc.num_iomem); numIomem > 0 {
+		cIomem := (*[1 << 28]C.libxl_iomem_range)(unsafe.Pointer(xc.iomem))[:numIomem:numIomem]
+		x.Iomem = make([]IomemRange, numIomem)
+		for i, v := range cIomem {
+			if err := x.Iomem[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 	if err := x.ClaimMode.fromC(&xc.claim_mode); err != nil {
@@ -762,18 +780,18 @@  func (x *DomainBuildInfo) fromC(xc *C.libxl_domain_build_info) error {
 	x.Tee = TeeType(xc.tee)
 	x.Type = DomainType(xc._type)
 	switch x.Type {
-	case DomainTypePv:
-		var typePv DomainBuildInfoTypeUnionPv
-		if err := typePv.fromC(xc); err != nil {
-			return err
-		}
-		x.TypeUnion = typePv
 	case DomainTypeHvm:
 		var typeHvm DomainBuildInfoTypeUnionHvm
 		if err := typeHvm.fromC(xc); err != nil {
 			return err
 		}
 		x.TypeUnion = typeHvm
+	case DomainTypePv:
+		var typePv DomainBuildInfoTypeUnionPv
+		if err := typePv.fromC(xc); err != nil {
+			return err
+		}
+		x.TypeUnion = typePv
 	case DomainTypePvh:
 		var typePvh DomainBuildInfoTypeUnionPvh
 		if err := typePvh.fromC(xc); err != nil {
@@ -953,29 +971,31 @@  func (x *DomainBuildInfo) toC() (xc C.libxl_domain_build_info, err error) {
 		C.libxl_domain_build_info_dispose(&xc)
 		return xc, err
 	}
-	numVcpuHardAffinity := len(x.VcpuHardAffinity)
-	xc.vcpu_hard_affinity = (*C.libxl_bitmap)(C.malloc(C.ulong(numVcpuHardAffinity) * C.sizeof_libxl_bitmap))
-	xc.num_vcpu_hard_affinity = C.int(numVcpuHardAffinity)
-	cVcpuHardAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_hard_affinity))[:numVcpuHardAffinity:numVcpuHardAffinity]
-	for i, v := range x.VcpuHardAffinity {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_build_info_dispose(&xc)
-			return xc, err
-		}
-		cVcpuHardAffinity[i] = tmp
-	}
-	numVcpuSoftAffinity := len(x.VcpuSoftAffinity)
-	xc.vcpu_soft_affinity = (*C.libxl_bitmap)(C.malloc(C.ulong(numVcpuSoftAffinity) * C.sizeof_libxl_bitmap))
-	xc.num_vcpu_soft_affinity = C.int(numVcpuSoftAffinity)
-	cVcpuSoftAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_soft_affinity))[:numVcpuSoftAffinity:numVcpuSoftAffinity]
-	for i, v := range x.VcpuSoftAffinity {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_build_info_dispose(&xc)
-			return xc, err
+	if numVcpuHardAffinity := len(x.VcpuHardAffinity); numVcpuHardAffinity > 0 {
+		xc.vcpu_hard_affinity = (*C.libxl_bitmap)(C.malloc(C.ulong(numVcpuHardAffinity) * C.sizeof_libxl_bitmap))
+		xc.num_vcpu_hard_affinity = C.int(numVcpuHardAffinity)
+		cVcpuHardAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_hard_affinity))[:numVcpuHardAffinity:numVcpuHardAffinity]
+		for i, v := range x.VcpuHardAffinity {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_build_info_dispose(&xc)
+				return xc, err
+			}
+			cVcpuHardAffinity[i] = tmp
+		}
+	}
+	if numVcpuSoftAffinity := len(x.VcpuSoftAffinity); numVcpuSoftAffinity > 0 {
+		xc.vcpu_soft_affinity = (*C.libxl_bitmap)(C.malloc(C.ulong(numVcpuSoftAffinity) * C.sizeof_libxl_bitmap))
+		xc.num_vcpu_soft_affinity = C.int(numVcpuSoftAffinity)
+		cVcpuSoftAffinity := (*[1 << 28]C.libxl_bitmap)(unsafe.Pointer(xc.vcpu_soft_affinity))[:numVcpuSoftAffinity:numVcpuSoftAffinity]
+		for i, v := range x.VcpuSoftAffinity {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_build_info_dispose(&xc)
+				return xc, err
+			}
+			cVcpuSoftAffinity[i] = tmp
 		}
-		cVcpuSoftAffinity[i] = tmp
 	}
 	xc.numa_placement, err = x.NumaPlacement.toC()
 	if err != nil {
@@ -1007,17 +1027,18 @@  func (x *DomainBuildInfo) toC() (xc C.libxl_domain_build_info, err error) {
 		return xc, err
 	}
 	xc.blkdev_start = C.CString(x.BlkdevStart)
-	numVnumaNodes := len(x.VnumaNodes)
-	xc.vnuma_nodes = (*C.libxl_vnode_info)(C.malloc(C.ulong(numVnumaNodes) * C.sizeof_libxl_vnode_info))
-	xc.num_vnuma_nodes = C.int(numVnumaNodes)
-	cVnumaNodes := (*[1 << 28]C.libxl_vnode_info)(unsafe.Pointer(xc.vnuma_nodes))[:numVnumaNodes:numVnumaNodes]
-	for i, v := range x.VnumaNodes {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_build_info_dispose(&xc)
-			return xc, err
+	if numVnumaNodes := len(x.VnumaNodes); numVnumaNodes > 0 {
+		xc.vnuma_nodes = (*C.libxl_vnode_info)(C.malloc(C.ulong(numVnumaNodes) * C.sizeof_libxl_vnode_info))
+		xc.num_vnuma_nodes = C.int(numVnumaNodes)
+		cVnumaNodes := (*[1 << 28]C.libxl_vnode_info)(unsafe.Pointer(xc.vnuma_nodes))[:numVnumaNodes:numVnumaNodes]
+		for i, v := range x.VnumaNodes {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_build_info_dispose(&xc)
+				return xc, err
+			}
+			cVnumaNodes[i] = tmp
 		}
-		cVnumaNodes[i] = tmp
 	}
 	xc.max_grant_frames = C.uint32_t(x.MaxGrantFrames)
 	xc.max_maptrack_frames = C.uint32_t(x.MaxMaptrackFrames)
@@ -1051,36 +1072,39 @@  func (x *DomainBuildInfo) toC() (xc C.libxl_domain_build_info, err error) {
 		C.libxl_domain_build_info_dispose(&xc)
 		return xc, err
 	}
-	numIoports := len(x.Ioports)
-	xc.ioports = (*C.libxl_ioport_range)(C.malloc(C.ulong(numIoports) * C.sizeof_libxl_ioport_range))
-	xc.num_ioports = C.int(numIoports)
-	cIoports := (*[1 << 28]C.libxl_ioport_range)(unsafe.Pointer(xc.ioports))[:numIoports:numIoports]
-	for i, v := range x.Ioports {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_build_info_dispose(&xc)
-			return xc, err
-		}
-		cIoports[i] = tmp
-	}
-	numIrqs := len(x.Irqs)
-	xc.irqs = (*C.uint32_t)(C.malloc(C.size_t(numIrqs * numIrqs)))
-	xc.num_irqs = C.int(numIrqs)
-	cIrqs := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.irqs))[:numIrqs:numIrqs]
-	for i, v := range x.Irqs {
-		cIrqs[i] = C.uint32_t(v)
-	}
-	numIomem := len(x.Iomem)
-	xc.iomem = (*C.libxl_iomem_range)(C.malloc(C.ulong(numIomem) * C.sizeof_libxl_iomem_range))
-	xc.num_iomem = C.int(numIomem)
-	cIomem := (*[1 << 28]C.libxl_iomem_range)(unsafe.Pointer(xc.iomem))[:numIomem:numIomem]
-	for i, v := range x.Iomem {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_build_info_dispose(&xc)
-			return xc, err
+	if numIoports := len(x.Ioports); numIoports > 0 {
+		xc.ioports = (*C.libxl_ioport_range)(C.malloc(C.ulong(numIoports) * C.sizeof_libxl_ioport_range))
+		xc.num_ioports = C.int(numIoports)
+		cIoports := (*[1 << 28]C.libxl_ioport_range)(unsafe.Pointer(xc.ioports))[:numIoports:numIoports]
+		for i, v := range x.Ioports {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_build_info_dispose(&xc)
+				return xc, err
+			}
+			cIoports[i] = tmp
+		}
+	}
+	if numIrqs := len(x.Irqs); numIrqs > 0 {
+		xc.irqs = (*C.uint32_t)(C.malloc(C.size_t(numIrqs * numIrqs)))
+		xc.num_irqs = C.int(numIrqs)
+		cIrqs := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.irqs))[:numIrqs:numIrqs]
+		for i, v := range x.Irqs {
+			cIrqs[i] = C.uint32_t(v)
+		}
+	}
+	if numIomem := len(x.Iomem); numIomem > 0 {
+		xc.iomem = (*C.libxl_iomem_range)(C.malloc(C.ulong(numIomem) * C.sizeof_libxl_iomem_range))
+		xc.num_iomem = C.int(numIomem)
+		cIomem := (*[1 << 28]C.libxl_iomem_range)(unsafe.Pointer(xc.iomem))[:numIomem:numIomem]
+		for i, v := range x.Iomem {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_build_info_dispose(&xc)
+				return xc, err
+			}
+			cIomem[i] = tmp
 		}
-		cIomem[i] = tmp
 	}
 	xc.claim_mode, err = x.ClaimMode.toC()
 	if err != nil {
@@ -1889,12 +1913,14 @@  func (x *DeviceVdispl) fromC(xc *C.libxl_device_vdispl) error {
 	x.BackendDomname = C.GoString(xc.backend_domname)
 	x.Devid = Devid(xc.devid)
 	x.BeAlloc = bool(xc.be_alloc)
-	numConnectors := int(xc.num_connectors)
-	cConnectors := (*[1 << 28]C.libxl_connector_param)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
-	x.Connectors = make([]ConnectorParam, numConnectors)
-	for i, v := range cConnectors {
-		if err := x.Connectors[i].fromC(&v); err != nil {
-			return err
+	x.Connectors = nil
+	if numConnectors := int(xc.num_connectors); numConnectors > 0 {
+		cConnectors := (*[1 << 28]C.libxl_connector_param)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
+		x.Connectors = make([]ConnectorParam, numConnectors)
+		for i, v := range cConnectors {
+			if err := x.Connectors[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -1907,33 +1933,38 @@  func (x *DeviceVdispl) toC() (xc C.libxl_device_vdispl, err error) {
 	xc.backend_domname = C.CString(x.BackendDomname)
 	xc.devid = C.libxl_devid(x.Devid)
 	xc.be_alloc = C.bool(x.BeAlloc)
-	numConnectors := len(x.Connectors)
-	xc.connectors = (*C.libxl_connector_param)(C.malloc(C.ulong(numConnectors) * C.sizeof_libxl_connector_param))
-	xc.num_connectors = C.int(numConnectors)
-	cConnectors := (*[1 << 28]C.libxl_connector_param)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
-	for i, v := range x.Connectors {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_device_vdispl_dispose(&xc)
-			return xc, err
+	if numConnectors := len(x.Connectors); numConnectors > 0 {
+		xc.connectors = (*C.libxl_connector_param)(C.malloc(C.ulong(numConnectors) * C.sizeof_libxl_connector_param))
+		xc.num_connectors = C.int(numConnectors)
+		cConnectors := (*[1 << 28]C.libxl_connector_param)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
+		for i, v := range x.Connectors {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_device_vdispl_dispose(&xc)
+				return xc, err
+			}
+			cConnectors[i] = tmp
 		}
-		cConnectors[i] = tmp
 	}
 	return xc, nil
 }
 
 func (x *VsndParams) fromC(xc *C.libxl_vsnd_params) error {
-	numSampleRates := int(xc.num_sample_rates)
-	cSampleRates := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.sample_rates))[:numSampleRates:numSampleRates]
-	x.SampleRates = make([]uint32, numSampleRates)
-	for i, v := range cSampleRates {
-		x.SampleRates[i] = uint32(v)
-	}
-	numSampleFormats := int(xc.num_sample_formats)
-	cSampleFormats := (*[1 << 28]C.libxl_vsnd_pcm_format)(unsafe.Pointer(xc.sample_formats))[:numSampleFormats:numSampleFormats]
-	x.SampleFormats = make([]VsndPcmFormat, numSampleFormats)
-	for i, v := range cSampleFormats {
-		x.SampleFormats[i] = VsndPcmFormat(v)
+	x.SampleRates = nil
+	if numSampleRates := int(xc.num_sample_rates); numSampleRates > 0 {
+		cSampleRates := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.sample_rates))[:numSampleRates:numSampleRates]
+		x.SampleRates = make([]uint32, numSampleRates)
+		for i, v := range cSampleRates {
+			x.SampleRates[i] = uint32(v)
+		}
+	}
+	x.SampleFormats = nil
+	if numSampleFormats := int(xc.num_sample_formats); numSampleFormats > 0 {
+		cSampleFormats := (*[1 << 28]C.libxl_vsnd_pcm_format)(unsafe.Pointer(xc.sample_formats))[:numSampleFormats:numSampleFormats]
+		x.SampleFormats = make([]VsndPcmFormat, numSampleFormats)
+		for i, v := range cSampleFormats {
+			x.SampleFormats[i] = VsndPcmFormat(v)
+		}
 	}
 	x.ChannelsMin = uint32(xc.channels_min)
 	x.ChannelsMax = uint32(xc.channels_max)
@@ -1944,19 +1975,21 @@  func (x *VsndParams) fromC(xc *C.libxl_vsnd_params) error {
 
 func (x *VsndParams) toC() (xc C.libxl_vsnd_params, err error) {
 	C.libxl_vsnd_params_init(&xc)
-	numSampleRates := len(x.SampleRates)
-	xc.sample_rates = (*C.uint32_t)(C.malloc(C.size_t(numSampleRates * numSampleRates)))
-	xc.num_sample_rates = C.int(numSampleRates)
-	cSampleRates := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.sample_rates))[:numSampleRates:numSampleRates]
-	for i, v := range x.SampleRates {
-		cSampleRates[i] = C.uint32_t(v)
-	}
-	numSampleFormats := len(x.SampleFormats)
-	xc.sample_formats = (*C.libxl_vsnd_pcm_format)(C.malloc(C.size_t(numSampleFormats * numSampleFormats)))
-	xc.num_sample_formats = C.int(numSampleFormats)
-	cSampleFormats := (*[1 << 28]C.libxl_vsnd_pcm_format)(unsafe.Pointer(xc.sample_formats))[:numSampleFormats:numSampleFormats]
-	for i, v := range x.SampleFormats {
-		cSampleFormats[i] = C.libxl_vsnd_pcm_format(v)
+	if numSampleRates := len(x.SampleRates); numSampleRates > 0 {
+		xc.sample_rates = (*C.uint32_t)(C.malloc(C.size_t(numSampleRates * numSampleRates)))
+		xc.num_sample_rates = C.int(numSampleRates)
+		cSampleRates := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.sample_rates))[:numSampleRates:numSampleRates]
+		for i, v := range x.SampleRates {
+			cSampleRates[i] = C.uint32_t(v)
+		}
+	}
+	if numSampleFormats := len(x.SampleFormats); numSampleFormats > 0 {
+		xc.sample_formats = (*C.libxl_vsnd_pcm_format)(C.malloc(C.size_t(numSampleFormats * numSampleFormats)))
+		xc.num_sample_formats = C.int(numSampleFormats)
+		cSampleFormats := (*[1 << 28]C.libxl_vsnd_pcm_format)(unsafe.Pointer(xc.sample_formats))[:numSampleFormats:numSampleFormats]
+		for i, v := range x.SampleFormats {
+			cSampleFormats[i] = C.libxl_vsnd_pcm_format(v)
+		}
 	}
 	xc.channels_min = C.uint32_t(x.ChannelsMin)
 	xc.channels_max = C.uint32_t(x.ChannelsMax)
@@ -1991,12 +2024,14 @@  func (x *VsndPcm) fromC(xc *C.libxl_vsnd_pcm) error {
 	if err := x.Params.fromC(&xc.params); err != nil {
 		return err
 	}
-	numVsndStreams := int(xc.num_vsnd_streams)
-	cStreams := (*[1 << 28]C.libxl_vsnd_stream)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
-	x.Streams = make([]VsndStream, numVsndStreams)
-	for i, v := range cStreams {
-		if err := x.Streams[i].fromC(&v); err != nil {
-			return err
+	x.Streams = nil
+	if numVsndStreams := int(xc.num_vsnd_streams); numVsndStreams > 0 {
+		cStreams := (*[1 << 28]C.libxl_vsnd_stream)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
+		x.Streams = make([]VsndStream, numVsndStreams)
+		for i, v := range cStreams {
+			if err := x.Streams[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -2011,17 +2046,18 @@  func (x *VsndPcm) toC() (xc C.libxl_vsnd_pcm, err error) {
 		C.libxl_vsnd_pcm_dispose(&xc)
 		return xc, err
 	}
-	numVsndStreams := len(x.Streams)
-	xc.streams = (*C.libxl_vsnd_stream)(C.malloc(C.ulong(numVsndStreams) * C.sizeof_libxl_vsnd_stream))
-	xc.num_vsnd_streams = C.int(numVsndStreams)
-	cStreams := (*[1 << 28]C.libxl_vsnd_stream)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
-	for i, v := range x.Streams {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_vsnd_pcm_dispose(&xc)
-			return xc, err
+	if numVsndStreams := len(x.Streams); numVsndStreams > 0 {
+		xc.streams = (*C.libxl_vsnd_stream)(C.malloc(C.ulong(numVsndStreams) * C.sizeof_libxl_vsnd_stream))
+		xc.num_vsnd_streams = C.int(numVsndStreams)
+		cStreams := (*[1 << 28]C.libxl_vsnd_stream)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
+		for i, v := range x.Streams {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_vsnd_pcm_dispose(&xc)
+				return xc, err
+			}
+			cStreams[i] = tmp
 		}
-		cStreams[i] = tmp
 	}
 	return xc, nil
 }
@@ -2035,12 +2071,14 @@  func (x *DeviceVsnd) fromC(xc *C.libxl_device_vsnd) error {
 	if err := x.Params.fromC(&xc.params); err != nil {
 		return err
 	}
-	numVsndPcms := int(xc.num_vsnd_pcms)
-	cPcms := (*[1 << 28]C.libxl_vsnd_pcm)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
-	x.Pcms = make([]VsndPcm, numVsndPcms)
-	for i, v := range cPcms {
-		if err := x.Pcms[i].fromC(&v); err != nil {
-			return err
+	x.Pcms = nil
+	if numVsndPcms := int(xc.num_vsnd_pcms); numVsndPcms > 0 {
+		cPcms := (*[1 << 28]C.libxl_vsnd_pcm)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
+		x.Pcms = make([]VsndPcm, numVsndPcms)
+		for i, v := range cPcms {
+			if err := x.Pcms[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -2059,17 +2097,18 @@  func (x *DeviceVsnd) toC() (xc C.libxl_device_vsnd, err error) {
 		C.libxl_device_vsnd_dispose(&xc)
 		return xc, err
 	}
-	numVsndPcms := len(x.Pcms)
-	xc.pcms = (*C.libxl_vsnd_pcm)(C.malloc(C.ulong(numVsndPcms) * C.sizeof_libxl_vsnd_pcm))
-	xc.num_vsnd_pcms = C.int(numVsndPcms)
-	cPcms := (*[1 << 28]C.libxl_vsnd_pcm)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
-	for i, v := range x.Pcms {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_device_vsnd_dispose(&xc)
-			return xc, err
+	if numVsndPcms := len(x.Pcms); numVsndPcms > 0 {
+		xc.pcms = (*C.libxl_vsnd_pcm)(C.malloc(C.ulong(numVsndPcms) * C.sizeof_libxl_vsnd_pcm))
+		xc.num_vsnd_pcms = C.int(numVsndPcms)
+		cPcms := (*[1 << 28]C.libxl_vsnd_pcm)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
+		for i, v := range x.Pcms {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_device_vsnd_dispose(&xc)
+				return xc, err
+			}
+			cPcms[i] = tmp
 		}
-		cPcms[i] = tmp
 	}
 	return xc, nil
 }
@@ -2081,124 +2120,154 @@  func (x *DomainConfig) fromC(xc *C.libxl_domain_config) error {
 	if err := x.BInfo.fromC(&xc.b_info); err != nil {
 		return err
 	}
-	numDisks := int(xc.num_disks)
-	cDisks := (*[1 << 28]C.libxl_device_disk)(unsafe.Pointer(xc.disks))[:numDisks:numDisks]
-	x.Disks = make([]DeviceDisk, numDisks)
-	for i, v := range cDisks {
-		if err := x.Disks[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numNics := int(xc.num_nics)
-	cNics := (*[1 << 28]C.libxl_device_nic)(unsafe.Pointer(xc.nics))[:numNics:numNics]
-	x.Nics = make([]DeviceNic, numNics)
-	for i, v := range cNics {
-		if err := x.Nics[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numPcidevs := int(xc.num_pcidevs)
-	cPcidevs := (*[1 << 28]C.libxl_device_pci)(unsafe.Pointer(xc.pcidevs))[:numPcidevs:numPcidevs]
-	x.Pcidevs = make([]DevicePci, numPcidevs)
-	for i, v := range cPcidevs {
-		if err := x.Pcidevs[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numRdms := int(xc.num_rdms)
-	cRdms := (*[1 << 28]C.libxl_device_rdm)(unsafe.Pointer(xc.rdms))[:numRdms:numRdms]
-	x.Rdms = make([]DeviceRdm, numRdms)
-	for i, v := range cRdms {
-		if err := x.Rdms[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numDtdevs := int(xc.num_dtdevs)
-	cDtdevs := (*[1 << 28]C.libxl_device_dtdev)(unsafe.Pointer(xc.dtdevs))[:numDtdevs:numDtdevs]
-	x.Dtdevs = make([]DeviceDtdev, numDtdevs)
-	for i, v := range cDtdevs {
-		if err := x.Dtdevs[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numVfbs := int(xc.num_vfbs)
-	cVfbs := (*[1 << 28]C.libxl_device_vfb)(unsafe.Pointer(xc.vfbs))[:numVfbs:numVfbs]
-	x.Vfbs = make([]DeviceVfb, numVfbs)
-	for i, v := range cVfbs {
-		if err := x.Vfbs[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numVkbs := int(xc.num_vkbs)
-	cVkbs := (*[1 << 28]C.libxl_device_vkb)(unsafe.Pointer(xc.vkbs))[:numVkbs:numVkbs]
-	x.Vkbs = make([]DeviceVkb, numVkbs)
-	for i, v := range cVkbs {
-		if err := x.Vkbs[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numVtpms := int(xc.num_vtpms)
-	cVtpms := (*[1 << 28]C.libxl_device_vtpm)(unsafe.Pointer(xc.vtpms))[:numVtpms:numVtpms]
-	x.Vtpms = make([]DeviceVtpm, numVtpms)
-	for i, v := range cVtpms {
-		if err := x.Vtpms[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numP9S := int(xc.num_p9s)
-	cP9S := (*[1 << 28]C.libxl_device_p9)(unsafe.Pointer(xc.p9s))[:numP9S:numP9S]
-	x.P9S = make([]DeviceP9, numP9S)
-	for i, v := range cP9S {
-		if err := x.P9S[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numPvcallsifs := int(xc.num_pvcallsifs)
-	cPvcallsifs := (*[1 << 28]C.libxl_device_pvcallsif)(unsafe.Pointer(xc.pvcallsifs))[:numPvcallsifs:numPvcallsifs]
-	x.Pvcallsifs = make([]DevicePvcallsif, numPvcallsifs)
-	for i, v := range cPvcallsifs {
-		if err := x.Pvcallsifs[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numVdispls := int(xc.num_vdispls)
-	cVdispls := (*[1 << 28]C.libxl_device_vdispl)(unsafe.Pointer(xc.vdispls))[:numVdispls:numVdispls]
-	x.Vdispls = make([]DeviceVdispl, numVdispls)
-	for i, v := range cVdispls {
-		if err := x.Vdispls[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numVsnds := int(xc.num_vsnds)
-	cVsnds := (*[1 << 28]C.libxl_device_vsnd)(unsafe.Pointer(xc.vsnds))[:numVsnds:numVsnds]
-	x.Vsnds = make([]DeviceVsnd, numVsnds)
-	for i, v := range cVsnds {
-		if err := x.Vsnds[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numChannels := int(xc.num_channels)
-	cChannels := (*[1 << 28]C.libxl_device_channel)(unsafe.Pointer(xc.channels))[:numChannels:numChannels]
-	x.Channels = make([]DeviceChannel, numChannels)
-	for i, v := range cChannels {
-		if err := x.Channels[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numUsbctrls := int(xc.num_usbctrls)
-	cUsbctrls := (*[1 << 28]C.libxl_device_usbctrl)(unsafe.Pointer(xc.usbctrls))[:numUsbctrls:numUsbctrls]
-	x.Usbctrls = make([]DeviceUsbctrl, numUsbctrls)
-	for i, v := range cUsbctrls {
-		if err := x.Usbctrls[i].fromC(&v); err != nil {
-			return err
-		}
-	}
-	numUsbdevs := int(xc.num_usbdevs)
-	cUsbdevs := (*[1 << 28]C.libxl_device_usbdev)(unsafe.Pointer(xc.usbdevs))[:numUsbdevs:numUsbdevs]
-	x.Usbdevs = make([]DeviceUsbdev, numUsbdevs)
-	for i, v := range cUsbdevs {
-		if err := x.Usbdevs[i].fromC(&v); err != nil {
-			return err
+	x.Disks = nil
+	if numDisks := int(xc.num_disks); numDisks > 0 {
+		cDisks := (*[1 << 28]C.libxl_device_disk)(unsafe.Pointer(xc.disks))[:numDisks:numDisks]
+		x.Disks = make([]DeviceDisk, numDisks)
+		for i, v := range cDisks {
+			if err := x.Disks[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Nics = nil
+	if numNics := int(xc.num_nics); numNics > 0 {
+		cNics := (*[1 << 28]C.libxl_device_nic)(unsafe.Pointer(xc.nics))[:numNics:numNics]
+		x.Nics = make([]DeviceNic, numNics)
+		for i, v := range cNics {
+			if err := x.Nics[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Pcidevs = nil
+	if numPcidevs := int(xc.num_pcidevs); numPcidevs > 0 {
+		cPcidevs := (*[1 << 28]C.libxl_device_pci)(unsafe.Pointer(xc.pcidevs))[:numPcidevs:numPcidevs]
+		x.Pcidevs = make([]DevicePci, numPcidevs)
+		for i, v := range cPcidevs {
+			if err := x.Pcidevs[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Rdms = nil
+	if numRdms := int(xc.num_rdms); numRdms > 0 {
+		cRdms := (*[1 << 28]C.libxl_device_rdm)(unsafe.Pointer(xc.rdms))[:numRdms:numRdms]
+		x.Rdms = make([]DeviceRdm, numRdms)
+		for i, v := range cRdms {
+			if err := x.Rdms[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Dtdevs = nil
+	if numDtdevs := int(xc.num_dtdevs); numDtdevs > 0 {
+		cDtdevs := (*[1 << 28]C.libxl_device_dtdev)(unsafe.Pointer(xc.dtdevs))[:numDtdevs:numDtdevs]
+		x.Dtdevs = make([]DeviceDtdev, numDtdevs)
+		for i, v := range cDtdevs {
+			if err := x.Dtdevs[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Vfbs = nil
+	if numVfbs := int(xc.num_vfbs); numVfbs > 0 {
+		cVfbs := (*[1 << 28]C.libxl_device_vfb)(unsafe.Pointer(xc.vfbs))[:numVfbs:numVfbs]
+		x.Vfbs = make([]DeviceVfb, numVfbs)
+		for i, v := range cVfbs {
+			if err := x.Vfbs[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Vkbs = nil
+	if numVkbs := int(xc.num_vkbs); numVkbs > 0 {
+		cVkbs := (*[1 << 28]C.libxl_device_vkb)(unsafe.Pointer(xc.vkbs))[:numVkbs:numVkbs]
+		x.Vkbs = make([]DeviceVkb, numVkbs)
+		for i, v := range cVkbs {
+			if err := x.Vkbs[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Vtpms = nil
+	if numVtpms := int(xc.num_vtpms); numVtpms > 0 {
+		cVtpms := (*[1 << 28]C.libxl_device_vtpm)(unsafe.Pointer(xc.vtpms))[:numVtpms:numVtpms]
+		x.Vtpms = make([]DeviceVtpm, numVtpms)
+		for i, v := range cVtpms {
+			if err := x.Vtpms[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.P9S = nil
+	if numP9S := int(xc.num_p9s); numP9S > 0 {
+		cP9S := (*[1 << 28]C.libxl_device_p9)(unsafe.Pointer(xc.p9s))[:numP9S:numP9S]
+		x.P9S = make([]DeviceP9, numP9S)
+		for i, v := range cP9S {
+			if err := x.P9S[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Pvcallsifs = nil
+	if numPvcallsifs := int(xc.num_pvcallsifs); numPvcallsifs > 0 {
+		cPvcallsifs := (*[1 << 28]C.libxl_device_pvcallsif)(unsafe.Pointer(xc.pvcallsifs))[:numPvcallsifs:numPvcallsifs]
+		x.Pvcallsifs = make([]DevicePvcallsif, numPvcallsifs)
+		for i, v := range cPvcallsifs {
+			if err := x.Pvcallsifs[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Vdispls = nil
+	if numVdispls := int(xc.num_vdispls); numVdispls > 0 {
+		cVdispls := (*[1 << 28]C.libxl_device_vdispl)(unsafe.Pointer(xc.vdispls))[:numVdispls:numVdispls]
+		x.Vdispls = make([]DeviceVdispl, numVdispls)
+		for i, v := range cVdispls {
+			if err := x.Vdispls[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Vsnds = nil
+	if numVsnds := int(xc.num_vsnds); numVsnds > 0 {
+		cVsnds := (*[1 << 28]C.libxl_device_vsnd)(unsafe.Pointer(xc.vsnds))[:numVsnds:numVsnds]
+		x.Vsnds = make([]DeviceVsnd, numVsnds)
+		for i, v := range cVsnds {
+			if err := x.Vsnds[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Channels = nil
+	if numChannels := int(xc.num_channels); numChannels > 0 {
+		cChannels := (*[1 << 28]C.libxl_device_channel)(unsafe.Pointer(xc.channels))[:numChannels:numChannels]
+		x.Channels = make([]DeviceChannel, numChannels)
+		for i, v := range cChannels {
+			if err := x.Channels[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Usbctrls = nil
+	if numUsbctrls := int(xc.num_usbctrls); numUsbctrls > 0 {
+		cUsbctrls := (*[1 << 28]C.libxl_device_usbctrl)(unsafe.Pointer(xc.usbctrls))[:numUsbctrls:numUsbctrls]
+		x.Usbctrls = make([]DeviceUsbctrl, numUsbctrls)
+		for i, v := range cUsbctrls {
+			if err := x.Usbctrls[i].fromC(&v); err != nil {
+				return err
+			}
+		}
+	}
+	x.Usbdevs = nil
+	if numUsbdevs := int(xc.num_usbdevs); numUsbdevs > 0 {
+		cUsbdevs := (*[1 << 28]C.libxl_device_usbdev)(unsafe.Pointer(xc.usbdevs))[:numUsbdevs:numUsbdevs]
+		x.Usbdevs = make([]DeviceUsbdev, numUsbdevs)
+		for i, v := range cUsbdevs {
+			if err := x.Usbdevs[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 	x.OnPoweroff = ActionOnShutdown(xc.on_poweroff)
@@ -2222,185 +2291,200 @@  func (x *DomainConfig) toC() (xc C.libxl_domain_config, err error) {
 		C.libxl_domain_config_dispose(&xc)
 		return xc, err
 	}
-	numDisks := len(x.Disks)
-	xc.disks = (*C.libxl_device_disk)(C.malloc(C.ulong(numDisks) * C.sizeof_libxl_device_disk))
-	xc.num_disks = C.int(numDisks)
-	cDisks := (*[1 << 28]C.libxl_device_disk)(unsafe.Pointer(xc.disks))[:numDisks:numDisks]
-	for i, v := range x.Disks {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cDisks[i] = tmp
-	}
-	numNics := len(x.Nics)
-	xc.nics = (*C.libxl_device_nic)(C.malloc(C.ulong(numNics) * C.sizeof_libxl_device_nic))
-	xc.num_nics = C.int(numNics)
-	cNics := (*[1 << 28]C.libxl_device_nic)(unsafe.Pointer(xc.nics))[:numNics:numNics]
-	for i, v := range x.Nics {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cNics[i] = tmp
-	}
-	numPcidevs := len(x.Pcidevs)
-	xc.pcidevs = (*C.libxl_device_pci)(C.malloc(C.ulong(numPcidevs) * C.sizeof_libxl_device_pci))
-	xc.num_pcidevs = C.int(numPcidevs)
-	cPcidevs := (*[1 << 28]C.libxl_device_pci)(unsafe.Pointer(xc.pcidevs))[:numPcidevs:numPcidevs]
-	for i, v := range x.Pcidevs {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cPcidevs[i] = tmp
-	}
-	numRdms := len(x.Rdms)
-	xc.rdms = (*C.libxl_device_rdm)(C.malloc(C.ulong(numRdms) * C.sizeof_libxl_device_rdm))
-	xc.num_rdms = C.int(numRdms)
-	cRdms := (*[1 << 28]C.libxl_device_rdm)(unsafe.Pointer(xc.rdms))[:numRdms:numRdms]
-	for i, v := range x.Rdms {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cRdms[i] = tmp
-	}
-	numDtdevs := len(x.Dtdevs)
-	xc.dtdevs = (*C.libxl_device_dtdev)(C.malloc(C.ulong(numDtdevs) * C.sizeof_libxl_device_dtdev))
-	xc.num_dtdevs = C.int(numDtdevs)
-	cDtdevs := (*[1 << 28]C.libxl_device_dtdev)(unsafe.Pointer(xc.dtdevs))[:numDtdevs:numDtdevs]
-	for i, v := range x.Dtdevs {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cDtdevs[i] = tmp
-	}
-	numVfbs := len(x.Vfbs)
-	xc.vfbs = (*C.libxl_device_vfb)(C.malloc(C.ulong(numVfbs) * C.sizeof_libxl_device_vfb))
-	xc.num_vfbs = C.int(numVfbs)
-	cVfbs := (*[1 << 28]C.libxl_device_vfb)(unsafe.Pointer(xc.vfbs))[:numVfbs:numVfbs]
-	for i, v := range x.Vfbs {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cVfbs[i] = tmp
-	}
-	numVkbs := len(x.Vkbs)
-	xc.vkbs = (*C.libxl_device_vkb)(C.malloc(C.ulong(numVkbs) * C.sizeof_libxl_device_vkb))
-	xc.num_vkbs = C.int(numVkbs)
-	cVkbs := (*[1 << 28]C.libxl_device_vkb)(unsafe.Pointer(xc.vkbs))[:numVkbs:numVkbs]
-	for i, v := range x.Vkbs {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cVkbs[i] = tmp
-	}
-	numVtpms := len(x.Vtpms)
-	xc.vtpms = (*C.libxl_device_vtpm)(C.malloc(C.ulong(numVtpms) * C.sizeof_libxl_device_vtpm))
-	xc.num_vtpms = C.int(numVtpms)
-	cVtpms := (*[1 << 28]C.libxl_device_vtpm)(unsafe.Pointer(xc.vtpms))[:numVtpms:numVtpms]
-	for i, v := range x.Vtpms {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cVtpms[i] = tmp
-	}
-	numP9S := len(x.P9S)
-	xc.p9s = (*C.libxl_device_p9)(C.malloc(C.ulong(numP9S) * C.sizeof_libxl_device_p9))
-	xc.num_p9s = C.int(numP9S)
-	cP9S := (*[1 << 28]C.libxl_device_p9)(unsafe.Pointer(xc.p9s))[:numP9S:numP9S]
-	for i, v := range x.P9S {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cP9S[i] = tmp
-	}
-	numPvcallsifs := len(x.Pvcallsifs)
-	xc.pvcallsifs = (*C.libxl_device_pvcallsif)(C.malloc(C.ulong(numPvcallsifs) * C.sizeof_libxl_device_pvcallsif))
-	xc.num_pvcallsifs = C.int(numPvcallsifs)
-	cPvcallsifs := (*[1 << 28]C.libxl_device_pvcallsif)(unsafe.Pointer(xc.pvcallsifs))[:numPvcallsifs:numPvcallsifs]
-	for i, v := range x.Pvcallsifs {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cPvcallsifs[i] = tmp
-	}
-	numVdispls := len(x.Vdispls)
-	xc.vdispls = (*C.libxl_device_vdispl)(C.malloc(C.ulong(numVdispls) * C.sizeof_libxl_device_vdispl))
-	xc.num_vdispls = C.int(numVdispls)
-	cVdispls := (*[1 << 28]C.libxl_device_vdispl)(unsafe.Pointer(xc.vdispls))[:numVdispls:numVdispls]
-	for i, v := range x.Vdispls {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cVdispls[i] = tmp
-	}
-	numVsnds := len(x.Vsnds)
-	xc.vsnds = (*C.libxl_device_vsnd)(C.malloc(C.ulong(numVsnds) * C.sizeof_libxl_device_vsnd))
-	xc.num_vsnds = C.int(numVsnds)
-	cVsnds := (*[1 << 28]C.libxl_device_vsnd)(unsafe.Pointer(xc.vsnds))[:numVsnds:numVsnds]
-	for i, v := range x.Vsnds {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cVsnds[i] = tmp
-	}
-	numChannels := len(x.Channels)
-	xc.channels = (*C.libxl_device_channel)(C.malloc(C.ulong(numChannels) * C.sizeof_libxl_device_channel))
-	xc.num_channels = C.int(numChannels)
-	cChannels := (*[1 << 28]C.libxl_device_channel)(unsafe.Pointer(xc.channels))[:numChannels:numChannels]
-	for i, v := range x.Channels {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cChannels[i] = tmp
-	}
-	numUsbctrls := len(x.Usbctrls)
-	xc.usbctrls = (*C.libxl_device_usbctrl)(C.malloc(C.ulong(numUsbctrls) * C.sizeof_libxl_device_usbctrl))
-	xc.num_usbctrls = C.int(numUsbctrls)
-	cUsbctrls := (*[1 << 28]C.libxl_device_usbctrl)(unsafe.Pointer(xc.usbctrls))[:numUsbctrls:numUsbctrls]
-	for i, v := range x.Usbctrls {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
-		}
-		cUsbctrls[i] = tmp
-	}
-	numUsbdevs := len(x.Usbdevs)
-	xc.usbdevs = (*C.libxl_device_usbdev)(C.malloc(C.ulong(numUsbdevs) * C.sizeof_libxl_device_usbdev))
-	xc.num_usbdevs = C.int(numUsbdevs)
-	cUsbdevs := (*[1 << 28]C.libxl_device_usbdev)(unsafe.Pointer(xc.usbdevs))[:numUsbdevs:numUsbdevs]
-	for i, v := range x.Usbdevs {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_domain_config_dispose(&xc)
-			return xc, err
+	if numDisks := len(x.Disks); numDisks > 0 {
+		xc.disks = (*C.libxl_device_disk)(C.malloc(C.ulong(numDisks) * C.sizeof_libxl_device_disk))
+		xc.num_disks = C.int(numDisks)
+		cDisks := (*[1 << 28]C.libxl_device_disk)(unsafe.Pointer(xc.disks))[:numDisks:numDisks]
+		for i, v := range x.Disks {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cDisks[i] = tmp
+		}
+	}
+	if numNics := len(x.Nics); numNics > 0 {
+		xc.nics = (*C.libxl_device_nic)(C.malloc(C.ulong(numNics) * C.sizeof_libxl_device_nic))
+		xc.num_nics = C.int(numNics)
+		cNics := (*[1 << 28]C.libxl_device_nic)(unsafe.Pointer(xc.nics))[:numNics:numNics]
+		for i, v := range x.Nics {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cNics[i] = tmp
+		}
+	}
+	if numPcidevs := len(x.Pcidevs); numPcidevs > 0 {
+		xc.pcidevs = (*C.libxl_device_pci)(C.malloc(C.ulong(numPcidevs) * C.sizeof_libxl_device_pci))
+		xc.num_pcidevs = C.int(numPcidevs)
+		cPcidevs := (*[1 << 28]C.libxl_device_pci)(unsafe.Pointer(xc.pcidevs))[:numPcidevs:numPcidevs]
+		for i, v := range x.Pcidevs {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cPcidevs[i] = tmp
+		}
+	}
+	if numRdms := len(x.Rdms); numRdms > 0 {
+		xc.rdms = (*C.libxl_device_rdm)(C.malloc(C.ulong(numRdms) * C.sizeof_libxl_device_rdm))
+		xc.num_rdms = C.int(numRdms)
+		cRdms := (*[1 << 28]C.libxl_device_rdm)(unsafe.Pointer(xc.rdms))[:numRdms:numRdms]
+		for i, v := range x.Rdms {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cRdms[i] = tmp
+		}
+	}
+	if numDtdevs := len(x.Dtdevs); numDtdevs > 0 {
+		xc.dtdevs = (*C.libxl_device_dtdev)(C.malloc(C.ulong(numDtdevs) * C.sizeof_libxl_device_dtdev))
+		xc.num_dtdevs = C.int(numDtdevs)
+		cDtdevs := (*[1 << 28]C.libxl_device_dtdev)(unsafe.Pointer(xc.dtdevs))[:numDtdevs:numDtdevs]
+		for i, v := range x.Dtdevs {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cDtdevs[i] = tmp
+		}
+	}
+	if numVfbs := len(x.Vfbs); numVfbs > 0 {
+		xc.vfbs = (*C.libxl_device_vfb)(C.malloc(C.ulong(numVfbs) * C.sizeof_libxl_device_vfb))
+		xc.num_vfbs = C.int(numVfbs)
+		cVfbs := (*[1 << 28]C.libxl_device_vfb)(unsafe.Pointer(xc.vfbs))[:numVfbs:numVfbs]
+		for i, v := range x.Vfbs {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cVfbs[i] = tmp
+		}
+	}
+	if numVkbs := len(x.Vkbs); numVkbs > 0 {
+		xc.vkbs = (*C.libxl_device_vkb)(C.malloc(C.ulong(numVkbs) * C.sizeof_libxl_device_vkb))
+		xc.num_vkbs = C.int(numVkbs)
+		cVkbs := (*[1 << 28]C.libxl_device_vkb)(unsafe.Pointer(xc.vkbs))[:numVkbs:numVkbs]
+		for i, v := range x.Vkbs {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cVkbs[i] = tmp
+		}
+	}
+	if numVtpms := len(x.Vtpms); numVtpms > 0 {
+		xc.vtpms = (*C.libxl_device_vtpm)(C.malloc(C.ulong(numVtpms) * C.sizeof_libxl_device_vtpm))
+		xc.num_vtpms = C.int(numVtpms)
+		cVtpms := (*[1 << 28]C.libxl_device_vtpm)(unsafe.Pointer(xc.vtpms))[:numVtpms:numVtpms]
+		for i, v := range x.Vtpms {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cVtpms[i] = tmp
+		}
+	}
+	if numP9S := len(x.P9S); numP9S > 0 {
+		xc.p9s = (*C.libxl_device_p9)(C.malloc(C.ulong(numP9S) * C.sizeof_libxl_device_p9))
+		xc.num_p9s = C.int(numP9S)
+		cP9S := (*[1 << 28]C.libxl_device_p9)(unsafe.Pointer(xc.p9s))[:numP9S:numP9S]
+		for i, v := range x.P9S {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cP9S[i] = tmp
+		}
+	}
+	if numPvcallsifs := len(x.Pvcallsifs); numPvcallsifs > 0 {
+		xc.pvcallsifs = (*C.libxl_device_pvcallsif)(C.malloc(C.ulong(numPvcallsifs) * C.sizeof_libxl_device_pvcallsif))
+		xc.num_pvcallsifs = C.int(numPvcallsifs)
+		cPvcallsifs := (*[1 << 28]C.libxl_device_pvcallsif)(unsafe.Pointer(xc.pvcallsifs))[:numPvcallsifs:numPvcallsifs]
+		for i, v := range x.Pvcallsifs {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cPvcallsifs[i] = tmp
+		}
+	}
+	if numVdispls := len(x.Vdispls); numVdispls > 0 {
+		xc.vdispls = (*C.libxl_device_vdispl)(C.malloc(C.ulong(numVdispls) * C.sizeof_libxl_device_vdispl))
+		xc.num_vdispls = C.int(numVdispls)
+		cVdispls := (*[1 << 28]C.libxl_device_vdispl)(unsafe.Pointer(xc.vdispls))[:numVdispls:numVdispls]
+		for i, v := range x.Vdispls {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cVdispls[i] = tmp
+		}
+	}
+	if numVsnds := len(x.Vsnds); numVsnds > 0 {
+		xc.vsnds = (*C.libxl_device_vsnd)(C.malloc(C.ulong(numVsnds) * C.sizeof_libxl_device_vsnd))
+		xc.num_vsnds = C.int(numVsnds)
+		cVsnds := (*[1 << 28]C.libxl_device_vsnd)(unsafe.Pointer(xc.vsnds))[:numVsnds:numVsnds]
+		for i, v := range x.Vsnds {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cVsnds[i] = tmp
+		}
+	}
+	if numChannels := len(x.Channels); numChannels > 0 {
+		xc.channels = (*C.libxl_device_channel)(C.malloc(C.ulong(numChannels) * C.sizeof_libxl_device_channel))
+		xc.num_channels = C.int(numChannels)
+		cChannels := (*[1 << 28]C.libxl_device_channel)(unsafe.Pointer(xc.channels))[:numChannels:numChannels]
+		for i, v := range x.Channels {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cChannels[i] = tmp
+		}
+	}
+	if numUsbctrls := len(x.Usbctrls); numUsbctrls > 0 {
+		xc.usbctrls = (*C.libxl_device_usbctrl)(C.malloc(C.ulong(numUsbctrls) * C.sizeof_libxl_device_usbctrl))
+		xc.num_usbctrls = C.int(numUsbctrls)
+		cUsbctrls := (*[1 << 28]C.libxl_device_usbctrl)(unsafe.Pointer(xc.usbctrls))[:numUsbctrls:numUsbctrls]
+		for i, v := range x.Usbctrls {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cUsbctrls[i] = tmp
+		}
+	}
+	if numUsbdevs := len(x.Usbdevs); numUsbdevs > 0 {
+		xc.usbdevs = (*C.libxl_device_usbdev)(C.malloc(C.ulong(numUsbdevs) * C.sizeof_libxl_device_usbdev))
+		xc.num_usbdevs = C.int(numUsbdevs)
+		cUsbdevs := (*[1 << 28]C.libxl_device_usbdev)(unsafe.Pointer(xc.usbdevs))[:numUsbdevs:numUsbdevs]
+		for i, v := range x.Usbdevs {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_domain_config_dispose(&xc)
+				return xc, err
+			}
+			cUsbdevs[i] = tmp
 		}
-		cUsbdevs[i] = tmp
 	}
 	xc.on_poweroff = C.libxl_action_on_shutdown(x.OnPoweroff)
 	xc.on_reboot = C.libxl_action_on_shutdown(x.OnReboot)
@@ -2658,12 +2742,14 @@  func (x *Vdisplinfo) fromC(xc *C.libxl_vdisplinfo) error {
 	x.Devid = Devid(xc.devid)
 	x.State = int(xc.state)
 	x.BeAlloc = bool(xc.be_alloc)
-	numConnectors := int(xc.num_connectors)
-	cConnectors := (*[1 << 28]C.libxl_connectorinfo)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
-	x.Connectors = make([]Connectorinfo, numConnectors)
-	for i, v := range cConnectors {
-		if err := x.Connectors[i].fromC(&v); err != nil {
-			return err
+	x.Connectors = nil
+	if numConnectors := int(xc.num_connectors); numConnectors > 0 {
+		cConnectors := (*[1 << 28]C.libxl_connectorinfo)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
+		x.Connectors = make([]Connectorinfo, numConnectors)
+		for i, v := range cConnectors {
+			if err := x.Connectors[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -2679,17 +2765,18 @@  func (x *Vdisplinfo) toC() (xc C.libxl_vdisplinfo, err error) {
 	xc.devid = C.libxl_devid(x.Devid)
 	xc.state = C.int(x.State)
 	xc.be_alloc = C.bool(x.BeAlloc)
-	numConnectors := len(x.Connectors)
-	xc.connectors = (*C.libxl_connectorinfo)(C.malloc(C.ulong(numConnectors) * C.sizeof_libxl_connectorinfo))
-	xc.num_connectors = C.int(numConnectors)
-	cConnectors := (*[1 << 28]C.libxl_connectorinfo)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
-	for i, v := range x.Connectors {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_vdisplinfo_dispose(&xc)
-			return xc, err
+	if numConnectors := len(x.Connectors); numConnectors > 0 {
+		xc.connectors = (*C.libxl_connectorinfo)(C.malloc(C.ulong(numConnectors) * C.sizeof_libxl_connectorinfo))
+		xc.num_connectors = C.int(numConnectors)
+		cConnectors := (*[1 << 28]C.libxl_connectorinfo)(unsafe.Pointer(xc.connectors))[:numConnectors:numConnectors]
+		for i, v := range x.Connectors {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_vdisplinfo_dispose(&xc)
+				return xc, err
+			}
+			cConnectors[i] = tmp
 		}
-		cConnectors[i] = tmp
 	}
 	return xc, nil
 }
@@ -2709,12 +2796,14 @@  func (x *Streaminfo) toC() (xc C.libxl_streaminfo, err error) {
 }
 
 func (x *Pcminfo) fromC(xc *C.libxl_pcminfo) error {
-	numVsndStreams := int(xc.num_vsnd_streams)
-	cStreams := (*[1 << 28]C.libxl_streaminfo)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
-	x.Streams = make([]Streaminfo, numVsndStreams)
-	for i, v := range cStreams {
-		if err := x.Streams[i].fromC(&v); err != nil {
-			return err
+	x.Streams = nil
+	if numVsndStreams := int(xc.num_vsnd_streams); numVsndStreams > 0 {
+		cStreams := (*[1 << 28]C.libxl_streaminfo)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
+		x.Streams = make([]Streaminfo, numVsndStreams)
+		for i, v := range cStreams {
+			if err := x.Streams[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -2723,17 +2812,18 @@  func (x *Pcminfo) fromC(xc *C.libxl_pcminfo) error {
 
 func (x *Pcminfo) toC() (xc C.libxl_pcminfo, err error) {
 	C.libxl_pcminfo_init(&xc)
-	numVsndStreams := len(x.Streams)
-	xc.streams = (*C.libxl_streaminfo)(C.malloc(C.ulong(numVsndStreams) * C.sizeof_libxl_streaminfo))
-	xc.num_vsnd_streams = C.int(numVsndStreams)
-	cStreams := (*[1 << 28]C.libxl_streaminfo)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
-	for i, v := range x.Streams {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_pcminfo_dispose(&xc)
-			return xc, err
+	if numVsndStreams := len(x.Streams); numVsndStreams > 0 {
+		xc.streams = (*C.libxl_streaminfo)(C.malloc(C.ulong(numVsndStreams) * C.sizeof_libxl_streaminfo))
+		xc.num_vsnd_streams = C.int(numVsndStreams)
+		cStreams := (*[1 << 28]C.libxl_streaminfo)(unsafe.Pointer(xc.streams))[:numVsndStreams:numVsndStreams]
+		for i, v := range x.Streams {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_pcminfo_dispose(&xc)
+				return xc, err
+			}
+			cStreams[i] = tmp
 		}
-		cStreams[i] = tmp
 	}
 	return xc, nil
 }
@@ -2745,12 +2835,14 @@  func (x *Vsndinfo) fromC(xc *C.libxl_vsndinfo) error {
 	x.FrontendId = uint32(xc.frontend_id)
 	x.Devid = Devid(xc.devid)
 	x.State = int(xc.state)
-	numVsndPcms := int(xc.num_vsnd_pcms)
-	cPcms := (*[1 << 28]C.libxl_pcminfo)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
-	x.Pcms = make([]Pcminfo, numVsndPcms)
-	for i, v := range cPcms {
-		if err := x.Pcms[i].fromC(&v); err != nil {
-			return err
+	x.Pcms = nil
+	if numVsndPcms := int(xc.num_vsnd_pcms); numVsndPcms > 0 {
+		cPcms := (*[1 << 28]C.libxl_pcminfo)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
+		x.Pcms = make([]Pcminfo, numVsndPcms)
+		for i, v := range cPcms {
+			if err := x.Pcms[i].fromC(&v); err != nil {
+				return err
+			}
 		}
 	}
 
@@ -2765,17 +2857,18 @@  func (x *Vsndinfo) toC() (xc C.libxl_vsndinfo, err error) {
 	xc.frontend_id = C.uint32_t(x.FrontendId)
 	xc.devid = C.libxl_devid(x.Devid)
 	xc.state = C.int(x.State)
-	numVsndPcms := len(x.Pcms)
-	xc.pcms = (*C.libxl_pcminfo)(C.malloc(C.ulong(numVsndPcms) * C.sizeof_libxl_pcminfo))
-	xc.num_vsnd_pcms = C.int(numVsndPcms)
-	cPcms := (*[1 << 28]C.libxl_pcminfo)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
-	for i, v := range x.Pcms {
-		tmp, err := v.toC()
-		if err != nil {
-			C.libxl_vsndinfo_dispose(&xc)
-			return xc, err
+	if numVsndPcms := len(x.Pcms); numVsndPcms > 0 {
+		xc.pcms = (*C.libxl_pcminfo)(C.malloc(C.ulong(numVsndPcms) * C.sizeof_libxl_pcminfo))
+		xc.num_vsnd_pcms = C.int(numVsndPcms)
+		cPcms := (*[1 << 28]C.libxl_pcminfo)(unsafe.Pointer(xc.pcms))[:numVsndPcms:numVsndPcms]
+		for i, v := range x.Pcms {
+			tmp, err := v.toC()
+			if err != nil {
+				C.libxl_vsndinfo_dispose(&xc)
+				return xc, err
+			}
+			cPcms[i] = tmp
 		}
-		cPcms[i] = tmp
 	}
 	return xc, nil
 }
@@ -2809,11 +2902,13 @@  func (x *Vkbinfo) toC() (xc C.libxl_vkbinfo, err error) {
 func (x *Numainfo) fromC(xc *C.libxl_numainfo) error {
 	x.Size = uint64(xc.size)
 	x.Free = uint64(xc.free)
-	numDists := int(xc.num_dists)
-	cDists := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.dists))[:numDists:numDists]
-	x.Dists = make([]uint32, numDists)
-	for i, v := range cDists {
-		x.Dists[i] = uint32(v)
+	x.Dists = nil
+	if numDists := int(xc.num_dists); numDists > 0 {
+		cDists := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.dists))[:numDists:numDists]
+		x.Dists = make([]uint32, numDists)
+		for i, v := range cDists {
+			x.Dists[i] = uint32(v)
+		}
 	}
 
 	return nil
@@ -2823,12 +2918,13 @@  func (x *Numainfo) toC() (xc C.libxl_numainfo, err error) {
 	C.libxl_numainfo_init(&xc)
 	xc.size = C.uint64_t(x.Size)
 	xc.free = C.uint64_t(x.Free)
-	numDists := len(x.Dists)
-	xc.dists = (*C.uint32_t)(C.malloc(C.size_t(numDists * numDists)))
-	xc.num_dists = C.int(numDists)
-	cDists := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.dists))[:numDists:numDists]
-	for i, v := range x.Dists {
-		cDists[i] = C.uint32_t(v)
+	if numDists := len(x.Dists); numDists > 0 {
+		xc.dists = (*C.uint32_t)(C.malloc(C.size_t(numDists * numDists)))
+		xc.num_dists = C.int(numDists)
+		cDists := (*[1 << 28]C.uint32_t)(unsafe.Pointer(xc.dists))[:numDists:numDists]
+		for i, v := range x.Dists {
+			cDists[i] = C.uint32_t(v)
+		}
 	}
 	return xc, nil
 }
@@ -2976,12 +3072,6 @@  func (x *Event) fromC(xc *C.libxl_event) error {
 	x.ForUser = uint64(xc.for_user)
 	x.Type = EventType(xc._type)
 	switch x.Type {
-	case EventTypeOperationComplete:
-		var typeOperationComplete EventTypeUnionOperationComplete
-		if err := typeOperationComplete.fromC(xc); err != nil {
-			return err
-		}
-		x.TypeUnion = typeOperationComplete
 	case EventTypeDomainShutdown:
 		var typeDomainShutdown EventTypeUnionDomainShutdown
 		if err := typeDomainShutdown.fromC(xc); err != nil {
@@ -2994,6 +3084,12 @@  func (x *Event) fromC(xc *C.libxl_event) error {
 			return err
 		}
 		x.TypeUnion = typeDiskEject
+	case EventTypeOperationComplete:
+		var typeOperationComplete EventTypeUnionOperationComplete
+		if err := typeOperationComplete.fromC(xc); err != nil {
+			return err
+		}
+		x.TypeUnion = typeOperationComplete
 	default:
 		return fmt.Errorf("invalid union key '%v'", x.Type)
 	}
@@ -3113,18 +3209,18 @@  func (x *PsrHwInfo) fromC(xc *C.libxl_psr_hw_info) error {
 	x.Id = uint32(xc.id)
 	x.Type = PsrFeatType(xc._type)
 	switch x.Type {
-	case PsrFeatTypeMba:
-		var typeMba PsrHwInfoTypeUnionMba
-		if err := typeMba.fromC(xc); err != nil {
-			return err
-		}
-		x.TypeUnion = typeMba
 	case PsrFeatTypeCat:
 		var typeCat PsrHwInfoTypeUnionCat
 		if err := typeCat.fromC(xc); err != nil {
 			return err
 		}
 		x.TypeUnion = typeCat
+	case PsrFeatTypeMba:
+		var typeMba PsrHwInfoTypeUnionMba
+		if err := typeMba.fromC(xc); err != nil {
+			return err
+		}
+		x.TypeUnion = typeMba
 	default:
 		return fmt.Errorf("invalid union key '%v'", x.Type)
 	}