fix(arm): grow slice not clear mem (#674)

internal/rt/growslice.go

@@ -20,8 +20,13 @@ package rt
 
 import "unsafe"
 
-func GrowSlice(et *GoType, old GoSlice, cap int) GoSlice {
-	s := growslice(old.Ptr, cap, old.Cap, cap - old.Len, et)
+// Growslice to newCap, not append length
+// Note: the [old, newCap) will not be zeroed if et does not have any ptr data.
+func GrowSlice(et *GoType, old GoSlice, newCap int) GoSlice {
+	if newCap < old.Len {
+		panic("growslice's newCap is smaller than old length")
+	}
+	s := growslice(old.Ptr, newCap, old.Cap, newCap - old.Len, et)
 	s.Len = old.Len
 	return s
 }

internal/rt/stubs.go

@@ -127,3 +127,39 @@ func GetMap64Assign(vt reflect.Type) Map64Assign {
 
 var emptyBytes = make([]byte, 0, 0)
 var EmptySlice = *(*GoSlice)(unsafe.Pointer(&emptyBytes))
+
+//go:linkname makeslice runtime.makeslice
+//goland:noinspection GoUnusedParameter
+func makeslice(et *GoType, len int, cap int) unsafe.Pointer
+
+func MakeSlice(oldPtr unsafe.Pointer, et *GoType, newLen int) *GoSlice {
+	if newLen == 0 {
+		return &EmptySlice
+	}
+
+	if *(*unsafe.Pointer)(oldPtr) == nil {
+		return &GoSlice{
+			Ptr: makeslice(et, newLen, newLen),
+			Len: newLen,
+			Cap: newLen,
+		}
+	}
+
+	old := (*GoSlice)(oldPtr)
+	if old.Cap >= newLen {
+		old.Len = newLen
+		return old
+	}
+
+	new := GrowSlice(et, *old, newLen)
+
+	// we sould clear the memory from [oldLen:newLen]
+	if et.PtrData == 0 {
+		oldlenmem := uintptr(old.Len) * et.Size
+		newlenmem := uintptr(newLen) * et.Size
+		MemclrNoHeapPointers(add(new.Ptr, oldlenmem), newlenmem-oldlenmem)
+	}
+
+	new.Len = newLen
+	return &new
+}

internal/rt/stubs_test.go

@@ -0,0 +1,30 @@
+package rt
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/assert"
+)
+
+
+func TestStubsMake(t *testing.T) {
+	t.Run("NonPtr", func(t *testing.T) {
+		old := &[]int{}
+		news := MakeSlice(unsafe.Pointer(old),  UnpackType(reflect.TypeOf(int(1))), 10000)
+		new := *(*[]int)(unsafe.Pointer(news))
+		for i := 0; i < 10000; i++ {
+			assert.Equal(t, new[i], 0)
+		}
+	})
+
+	t.Run("HasPtr", func(t *testing.T) {
+		old := &[]*int{}
+		news := MakeSlice(unsafe.Pointer(old),  UnpackType(reflect.TypeOf((*int)(nil))), 10000)
+		new := *(*[]*int)(unsafe.Pointer(news))
+		for i := 0; i < 10000; i++ {
+			assert.Equal(t, new[i], (*int)(nil))
+		}
+	})
+}