[syserror] Remove syserror from go_marshal

PiperOrigin-RevId: 368470656

15 files changed, 157 insertions, 117 deletions

diff --git a/pkg/gohacks/BUILD b/pkg/gohacks/BUILD
index 35683fe98..b4e05f922 100644
--- a/pkg/gohacks/BUILD
+++ b/pkg/gohacks/BUILD
@@ -1,4 +1,4 @@
-load("//tools:defs.bzl", "go_library")
+load("//tools:defs.bzl", "go_library", "go_test")
 
 package(licenses = ["notice"])
 
@@ -10,3 +10,11 @@ go_library(
     stateify = False,
     visibility = ["//:sandbox"],
 )
+
+go_test(
+    name = "gohacks_test",
+    size = "small",
+    srcs = ["gohacks_test.go"],
+    library = ":gohacks",
+    deps = ["@org_golang_x_sys//unix:go_default_library"],
+)
diff --git a/pkg/gohacks/gohacks_test.go b/pkg/gohacks/gohacks_test.go
new file mode 100644
index 000000000..e18c8abc7
--- /dev/null
+++ b/pkg/gohacks/gohacks_test.go
@@ -0,0 +1,97 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package gohacks
+
+import (
+	"io/ioutil"
+	"math/rand"
+	"os"
+	"runtime/debug"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+func randBuf(size int) []byte {
+	b := make([]byte, size)
+	for i := range b {
+		b[i] = byte(rand.Intn(256))
+	}
+	return b
+}
+
+// Size of a page in bytes. Cloned from hostarch.PageSize to avoid a circular
+// dependency.
+const pageSize = 4096
+
+func testCopy(dst, src []byte) (panicked bool) {
+	defer func() {
+		if r := recover(); r != nil {
+			panicked = true
+		}
+	}()
+	debug.SetPanicOnFault(true)
+	copy(dst, src)
+	return panicked
+}
+
+func TestSegVOnMemmove(t *testing.T) {
+	// Test that SIGSEGVs received by runtime.memmove when *not* doing
+	// CopyIn or CopyOut work gets propagated to the runtime.
+	const bufLen = pageSize
+	a, err := unix.Mmap(-1, 0, bufLen, unix.PROT_NONE, unix.MAP_ANON|unix.MAP_PRIVATE)
+	if err != nil {
+		t.Fatalf("Mmap failed: %v", err)
+
+	}
+	defer unix.Munmap(a)
+	b := randBuf(bufLen)
+
+	if !testCopy(b, a) {
+		t.Fatalf("testCopy didn't panic when it should have")
+	}
+
+	if !testCopy(a, b) {
+		t.Fatalf("testCopy didn't panic when it should have")
+	}
+}
+
+func TestSigbusOnMemmove(t *testing.T) {
+	// Test that SIGBUS received by runtime.memmove when *not* doing
+	// CopyIn or CopyOut work gets propagated to the runtime.
+	const bufLen = pageSize
+	f, err := ioutil.TempFile("", "sigbus_test")
+	if err != nil {
+		t.Fatalf("TempFile failed: %v", err)
+	}
+	os.Remove(f.Name())
+	defer f.Close()
+
+	a, err := unix.Mmap(int(f.Fd()), 0, bufLen, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
+	if err != nil {
+		t.Fatalf("Mmap failed: %v", err)
+
+	}
+	defer unix.Munmap(a)
+	b := randBuf(bufLen)
+
+	if !testCopy(b, a) {
+		t.Fatalf("testCopy didn't panic when it should have")
+	}
+
+	if !testCopy(a, b) {
+		t.Fatalf("testCopy didn't panic when it should have")
+	}
+}
diff --git a/pkg/gohacks/gohacks_unsafe.go b/pkg/gohacks/gohacks_unsafe.go
index 10bbb1f58..374aac2b4 100644
--- a/pkg/gohacks/gohacks_unsafe.go
+++ b/pkg/gohacks/gohacks_unsafe.go
@@ -75,3 +75,17 @@ func StringFromImmutableBytes(bs []byte) string {
 	// strings.Builder.String().
 	return *(*string)(unsafe.Pointer(&bs))
 }
+
+// Note that go:linkname silently doesn't work if the local name is exported,
+// necessitating an indirection for exported functions.
+
+// Memmove is runtime.memmove, exported for SeqAtomicLoad/SeqAtomicTryLoad<T>.
+//
+//go:nosplit
+func Memmove(to, from unsafe.Pointer, n uintptr) {
+	memmove(to, from, n)
+}
+
+//go:linkname memmove runtime.memmove
+//go:noescape
+func memmove(to, from unsafe.Pointer, n uintptr)
diff --git a/pkg/marshal/marshal.go b/pkg/marshal/marshal.go
index eb036feae..7da450ce8 100644
--- a/pkg/marshal/marshal.go
+++ b/pkg/marshal/marshal.go
@@ -166,6 +166,9 @@ type Marshallable interface {
 // %s is the first argument to the slice clause. This directive is not supported
 // for newtypes on arrays.
 //
+// Note: Partial copies are not supported for Slice API UnmarshalUnsafe and
+// MarshalUnsafe.
+//
 // The slice clause also takes an optional second argument, which must be the
 // value "inner":
 //
diff --git a/pkg/safecopy/safecopy_test.go b/pkg/safecopy/safecopy_test.go
index 611f36253..55743e69c 100644
--- a/pkg/safecopy/safecopy_test.go
+++ b/pkg/safecopy/safecopy_test.go
@@ -19,8 +19,6 @@ import (
 	"fmt"
 	"io/ioutil"
 	"math/rand"
-	"os"
-	"runtime/debug"
 	"testing"
 	"unsafe"
 
@@ -568,63 +566,3 @@ func TestCompareAndSwapUint32BusError(t *testing.T) {
 		}
 	})
 }
-
-func testCopy(dst, src []byte) (panicked bool) {
-	defer func() {
-		if r := recover(); r != nil {
-			panicked = true
-		}
-	}()
-	debug.SetPanicOnFault(true)
-	copy(dst, src)
-	return
-}
-
-func TestSegVOnMemmove(t *testing.T) {
-	// Test that SIGSEGVs received by runtime.memmove when *not* doing
-	// CopyIn or CopyOut work gets propagated to the runtime.
-	const bufLen = pageSize
-	a, err := unix.Mmap(-1, 0, bufLen, unix.PROT_NONE, unix.MAP_ANON|unix.MAP_PRIVATE)
-	if err != nil {
-		t.Fatalf("Mmap failed: %v", err)
-
-	}
-	defer unix.Munmap(a)
-	b := randBuf(bufLen)
-
-	if !testCopy(b, a) {
-		t.Fatalf("testCopy didn't panic when it should have")
-	}
-
-	if !testCopy(a, b) {
-		t.Fatalf("testCopy didn't panic when it should have")
-	}
-}
-
-func TestSigbusOnMemmove(t *testing.T) {
-	// Test that SIGBUS received by runtime.memmove when *not* doing
-	// CopyIn or CopyOut work gets propagated to the runtime.
-	const bufLen = pageSize
-	f, err := ioutil.TempFile("", "sigbus_test")
-	if err != nil {
-		t.Fatalf("TempFile failed: %v", err)
-	}
-	os.Remove(f.Name())
-	defer f.Close()
-
-	a, err := unix.Mmap(int(f.Fd()), 0, bufLen, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
-	if err != nil {
-		t.Fatalf("Mmap failed: %v", err)
-
-	}
-	defer unix.Munmap(a)
-	b := randBuf(bufLen)
-
-	if !testCopy(b, a) {
-		t.Fatalf("testCopy didn't panic when it should have")
-	}
-
-	if !testCopy(a, b) {
-		t.Fatalf("testCopy didn't panic when it should have")
-	}
-}
diff --git a/pkg/sentry/time/BUILD b/pkg/sentry/time/BUILD
index 87d8687ce..1f617ca8f 100644
--- a/pkg/sentry/time/BUILD
+++ b/pkg/sentry/time/BUILD
@@ -32,6 +32,7 @@ go_library(
     ],
     visibility = ["//:sandbox"],
     deps = [
+        "//pkg/gohacks",
         "//pkg/log",
         "//pkg/metric",
         "//pkg/sync",
diff --git a/pkg/sync/BUILD b/pkg/sync/BUILD
index b2c5229e7..8b3a11c64 100644
--- a/pkg/sync/BUILD
+++ b/pkg/sync/BUILD
@@ -43,6 +43,7 @@ go_template(
     ],
     deps = [
         ":sync",
+        "//pkg/gohacks",
     ],
 )
 
diff --git a/pkg/sync/generic_seqatomic_unsafe.go b/pkg/sync/generic_seqatomic_unsafe.go
index 82b676abf..9578c9c52 100644
--- a/pkg/sync/generic_seqatomic_unsafe.go
+++ b/pkg/sync/generic_seqatomic_unsafe.go
@@ -10,6 +10,7 @@ package seqatomic
 import (
 	"unsafe"
 
+	"gvisor.dev/gvisor/pkg/gohacks"
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
@@ -39,7 +40,7 @@ func SeqAtomicTryLoad(seq *sync.SeqCount, epoch sync.SeqCountEpoch, ptr *Value)
 		// runtime.RaceDisable() doesn't actually stop the race detector, so it
 		// can't help us here. Instead, call runtime.memmove directly, which is
 		// not instrumented by the race detector.
-		sync.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val))
+		gohacks.Memmove(unsafe.Pointer(&val), unsafe.Pointer(ptr), unsafe.Sizeof(val))
 	} else {
 		// This is ~40% faster for short reads than going through memmove.
 		val = *ptr
diff --git a/pkg/sync/runtime_unsafe.go b/pkg/sync/runtime_unsafe.go
index 158985709..39c766331 100644
--- a/pkg/sync/runtime_unsafe.go
+++ b/pkg/sync/runtime_unsafe.go
@@ -17,20 +17,6 @@ import (
 	"unsafe"
 )
 
-// Note that go:linkname silently doesn't work if the local name is exported,
-// necessitating an indirection for exported functions.
-
-// Memmove is runtime.memmove, exported for SeqAtomicLoad/SeqAtomicTryLoad<T>.
-//
-//go:nosplit
-func Memmove(to, from unsafe.Pointer, n uintptr) {
-	memmove(to, from, n)
-}
-
-//go:linkname memmove runtime.memmove
-//go:noescape
-func memmove(to, from unsafe.Pointer, n uintptr)
-
 // Gopark is runtime.gopark. Gopark calls unlockf(pointer to runtime.g, lock);
 // if unlockf returns true, Gopark blocks until Goready(pointer to runtime.g)
 // is called. unlockf and its callees must be nosplit and norace, since stack
diff --git a/pkg/sync/seqatomictest/BUILD b/pkg/sync/seqatomictest/BUILD
index 5c38c783e..5f9164117 100644
--- a/pkg/sync/seqatomictest/BUILD
+++ b/pkg/sync/seqatomictest/BUILD
@@ -18,6 +18,7 @@ go_library(
     name = "seqatomic",
     srcs = ["seqatomic_int_unsafe.go"],
     deps = [
+        "//pkg/gohacks",
         "//pkg/sync",
     ],
 )
diff --git a/tools/go_marshal/defs.bzl b/tools/go_marshal/defs.bzl
index e23901815..9f620cb76 100644
--- a/tools/go_marshal/defs.bzl
+++ b/tools/go_marshal/defs.bzl
@@ -57,7 +57,6 @@ go_marshal = rule(
 # marshal_deps are the dependencies requied by generated code.
 marshal_deps = [
     "//pkg/gohacks",
-    "//pkg/safecopy",
     "//pkg/hostarch",
     "//pkg/marshal",
 ]
diff --git a/tools/go_marshal/gomarshal/generator.go b/tools/go_marshal/gomarshal/generator.go
index 0e2d752cb..00961c90d 100644
--- a/tools/go_marshal/gomarshal/generator.go
+++ b/tools/go_marshal/gomarshal/generator.go
@@ -112,10 +112,8 @@ func NewGenerator(srcs []string, out, outTest, outTestUnconditional, pkg string,
 	g.imports.add("runtime")
 	g.imports.add("unsafe")
 	g.imports.add("gvisor.dev/gvisor/pkg/gohacks")
-	g.imports.add("gvisor.dev/gvisor/pkg/safecopy")
 	g.imports.add("gvisor.dev/gvisor/pkg/hostarch")
 	g.imports.add("gvisor.dev/gvisor/pkg/marshal")
-
 	return &g, nil
 }
 
diff --git a/tools/go_marshal/gomarshal/generator_interfaces_array_newtype.go b/tools/go_marshal/gomarshal/generator_interfaces_array_newtype.go
index 32afece2e..e8ce6e366 100644
--- a/tools/go_marshal/gomarshal/generator_interfaces_array_newtype.go
+++ b/tools/go_marshal/gomarshal/generator_interfaces_array_newtype.go
@@ -33,13 +33,13 @@ func (g *interfaceGenerator) validateArrayNewtype(n *ast.Ident, a *ast.ArrayType
 }
 
 func (g *interfaceGenerator) emitMarshallableForArrayNewtype(n *ast.Ident, a *ast.ArrayType, elt *ast.Ident) {
+	g.recordUsedImport("gohacks")
+	g.recordUsedImport("hostarch")
 	g.recordUsedImport("io")
 	g.recordUsedImport("marshal")
 	g.recordUsedImport("reflect")
 	g.recordUsedImport("runtime")
-	g.recordUsedImport("safecopy")
 	g.recordUsedImport("unsafe")
-	g.recordUsedImport("hostarch")
 
 	lenExpr := g.arrayLenExpr(a)
 
@@ -89,14 +89,14 @@ func (g *interfaceGenerator) emitMarshallableForArrayNewtype(n *ast.Ident, a *as
 	g.emit("// MarshalUnsafe implements marshal.Marshallable.MarshalUnsafe.\n")
 	g.emit("func (%s *%s) MarshalUnsafe(dst []byte) {\n", g.r, g.typeName())
 	g.inIndent(func() {
-		g.emit("safecopy.CopyIn(dst, unsafe.Pointer(%s))\n", g.r)
+		g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(&%s[0]), uintptr(len(dst)))\n", g.r)
 	})
 	g.emit("}\n\n")
 
 	g.emit("// UnmarshalUnsafe implements marshal.Marshallable.UnmarshalUnsafe.\n")
 	g.emit("func (%s *%s) UnmarshalUnsafe(src []byte) {\n", g.r, g.typeName())
 	g.inIndent(func() {
-		g.emit("safecopy.CopyOut(unsafe.Pointer(%s), src)\n", g.r)
+		g.emit("gohacks.Memmove(unsafe.Pointer(%s), unsafe.Pointer(&src[0]), uintptr(len(src)))\n", g.r)
 	})
 	g.emit("}\n\n")
 
diff --git a/tools/go_marshal/gomarshal/generator_interfaces_primitive_newtype.go b/tools/go_marshal/gomarshal/generator_interfaces_primitive_newtype.go
index 05f0e0db4..19aa5994a 100644
--- a/tools/go_marshal/gomarshal/generator_interfaces_primitive_newtype.go
+++ b/tools/go_marshal/gomarshal/generator_interfaces_primitive_newtype.go
@@ -95,13 +95,13 @@ func (g *interfaceGenerator) validatePrimitiveNewtype(t *ast.Ident) {
 // newtypes are always packed, so we can omit the various fallbacks required for
 // non-packed structs.
 func (g *interfaceGenerator) emitMarshallableForPrimitiveNewtype(nt *ast.Ident) {
+	g.recordUsedImport("gohacks")
+	g.recordUsedImport("hostarch")
 	g.recordUsedImport("io")
 	g.recordUsedImport("marshal")
 	g.recordUsedImport("reflect")
 	g.recordUsedImport("runtime")
-	g.recordUsedImport("safecopy")
 	g.recordUsedImport("unsafe")
-	g.recordUsedImport("hostarch")
 
 	g.emit("// SizeBytes implements marshal.Marshallable.SizeBytes.\n")
 	g.emit("//go:nosplit\n")
@@ -141,14 +141,14 @@ func (g *interfaceGenerator) emitMarshallableForPrimitiveNewtype(nt *ast.Ident)
 	g.emit("// MarshalUnsafe implements marshal.Marshallable.MarshalUnsafe.\n")
 	g.emit("func (%s *%s) MarshalUnsafe(dst []byte) {\n", g.r, g.typeName())
 	g.inIndent(func() {
-		g.emit("safecopy.CopyIn(dst, unsafe.Pointer(%s))\n", g.r)
+		g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(%s), uintptr(len(dst)))\n", g.r)
 	})
 	g.emit("}\n\n")
 
 	g.emit("// UnmarshalUnsafe implements marshal.Marshallable.UnmarshalUnsafe.\n")
 	g.emit("func (%s *%s) UnmarshalUnsafe(src []byte) {\n", g.r, g.typeName())
 	g.inIndent(func() {
-		g.emit("safecopy.CopyOut(unsafe.Pointer(%s), src)\n", g.r)
+		g.emit("gohacks.Memmove(unsafe.Pointer(%s), unsafe.Pointer(&src[0]), uintptr(len(src)))\n", g.r)
 	})
 	g.emit("}\n\n")
 
@@ -260,11 +260,9 @@ func (g *interfaceGenerator) emitMarshallableSliceForPrimitiveNewtype(nt *ast.Id
 		g.emit("}\n")
 		g.emit("size := (*%s)(nil).SizeBytes()\n\n", g.typeName())
 
-		g.emitNoEscapeSliceDataPointer("&src", "val")
-
-		g.emit("length, err := safecopy.CopyIn(dst[:(size*count)], val)\n")
-		g.emitKeepAlive("src")
-		g.emit("return length, err\n")
+		g.emit("dst = dst[:size*count]\n")
+		g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(&src[0]), uintptr(len(dst)))\n")
+		g.emit("return size*count, nil\n")
 	})
 	g.emit("}\n\n")
 
@@ -279,11 +277,9 @@ func (g *interfaceGenerator) emitMarshallableSliceForPrimitiveNewtype(nt *ast.Id
 		g.emit("}\n")
 		g.emit("size := (*%s)(nil).SizeBytes()\n\n", g.typeName())
 
-		g.emitNoEscapeSliceDataPointer("&dst", "val")
-
-		g.emit("length, err := safecopy.CopyOut(val, src[:(size*count)])\n")
-		g.emitKeepAlive("dst")
-		g.emit("return length, err\n")
+		g.emit("src = src[:(size*count)]\n")
+		g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(&src[0]), uintptr(len(src)))\n")
+		g.emit("return size*count, nil\n")
 	})
 	g.emit("}\n\n")
 }
diff --git a/tools/go_marshal/gomarshal/generator_interfaces_struct.go b/tools/go_marshal/gomarshal/generator_interfaces_struct.go
index 72df1ab64..087c88b54 100644
--- a/tools/go_marshal/gomarshal/generator_interfaces_struct.go
+++ b/tools/go_marshal/gomarshal/generator_interfaces_struct.go
@@ -270,18 +270,18 @@ func (g *interfaceGenerator) emitMarshallableForStruct(st *ast.StructType) {
 			g.emit("%s.MarshalBytes(dst)\n", g.r)
 		}
 		if thisPacked {
-			g.recordUsedImport("safecopy")
+			g.recordUsedImport("gohacks")
 			g.recordUsedImport("unsafe")
 			if cond, ok := g.areFieldsPackedExpression(); ok {
 				g.emit("if %s {\n", cond)
 				g.inIndent(func() {
-					g.emit("safecopy.CopyIn(dst, unsafe.Pointer(%s))\n", g.r)
+					g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(%s),  uintptr(len(dst)))\n", g.r)
 				})
 				g.emit("} else {\n")
 				g.inIndent(fallback)
 				g.emit("}\n")
 			} else {
-				g.emit("safecopy.CopyIn(dst, unsafe.Pointer(%s))\n", g.r)
+				g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(%s),  uintptr(len(dst)))\n", g.r)
 			}
 		} else {
 			fallback()
@@ -297,25 +297,23 @@ func (g *interfaceGenerator) emitMarshallableForStruct(st *ast.StructType) {
 			g.emit("%s.UnmarshalBytes(src)\n", g.r)
 		}
 		if thisPacked {
-			g.recordUsedImport("safecopy")
-			g.recordUsedImport("unsafe")
+			g.recordUsedImport("gohacks")
 			if cond, ok := g.areFieldsPackedExpression(); ok {
 				g.emit("if %s {\n", cond)
 				g.inIndent(func() {
-					g.emit("safecopy.CopyOut(unsafe.Pointer(%s), src)\n", g.r)
+					g.emit("gohacks.Memmove(unsafe.Pointer(%s), unsafe.Pointer(&src[0]), uintptr(len(src)))\n", g.r)
 				})
 				g.emit("} else {\n")
 				g.inIndent(fallback)
 				g.emit("}\n")
 			} else {
-				g.emit("safecopy.CopyOut(unsafe.Pointer(%s), src)\n", g.r)
+				g.emit("gohacks.Memmove(unsafe.Pointer(%s), unsafe.Pointer(&src[0]), uintptr(len(src)))\n", g.r)
 			}
 		} else {
 			fallback()
 		}
 	})
 	g.emit("}\n\n")
-
 	g.emit("// CopyOutN implements marshal.Marshallable.CopyOutN.\n")
 	g.emit("//go:nosplit\n")
 	g.recordUsedImport("marshal")
@@ -561,16 +559,15 @@ func (g *interfaceGenerator) emitMarshallableSliceForStruct(st *ast.StructType,
 			g.recordUsedImport("reflect")
 			g.recordUsedImport("runtime")
 			g.recordUsedImport("unsafe")
+			g.recordUsedImport("gohacks")
 			if _, ok := g.areFieldsPackedExpression(); ok {
 				g.emit("if !src[0].Packed() {\n")
 				g.inIndent(fallback)
 				g.emit("}\n\n")
 			}
-			g.emitNoEscapeSliceDataPointer("&src", "val")
-
-			g.emit("length, err := safecopy.CopyIn(dst[:(size*count)], val)\n")
-			g.emitKeepAlive("src")
-			g.emit("return length, err\n")
+			g.emit("dst = dst[:size*count]\n")
+			g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(&src[0]), uintptr(len(dst)))\n")
+			g.emit("return size * count, nil\n")
 		} else {
 			fallback()
 		}
@@ -598,19 +595,19 @@ func (g *interfaceGenerator) emitMarshallableSliceForStruct(st *ast.StructType,
 			g.emit("return size * count, nil\n")
 		}
 		if thisPacked {
+			g.recordUsedImport("gohacks")
 			g.recordUsedImport("reflect")
 			g.recordUsedImport("runtime")
-			g.recordUsedImport("unsafe")
 			if _, ok := g.areFieldsPackedExpression(); ok {
 				g.emit("if !dst[0].Packed() {\n")
 				g.inIndent(fallback)
 				g.emit("}\n\n")
 			}
-			g.emitNoEscapeSliceDataPointer("&dst", "val")
 
-			g.emit("length, err := safecopy.CopyOut(val, src[:(size*count)])\n")
-			g.emitKeepAlive("dst")
-			g.emit("return length, err\n")
+			g.emit("src = src[:(size*count)]\n")
+			g.emit("gohacks.Memmove(unsafe.Pointer(&dst[0]), unsafe.Pointer(&src[0]), uintptr(len(src)))\n")
+
+			g.emit("return count*size, nil\n")
 		} else {
 			fallback()
 		}