Fix: avoid writing Java null to native

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/structs/CStructAccess.java

@@ -1246,11 +1246,10 @@ public final boolean accepts(ArgDescriptor desc) {
             return desc.isPyObject();
         }
 
-        public final void writeArray(Object pointer, Object[] values) {
-            writeArray(pointer, values, values.length, 0, 0);
-        }
-
         public final void writeArray(Object pointer, Object[] values, int length, int sourceOffset, int targetOffset) {
+            if (length > values.length) {
+                throw CompilerDirectives.shouldNotReachHere();
+            }
             for (int i = 0; i < length; i++) {
                 execute(pointer, (i + targetOffset) * POINTER_SIZE, values[i + sourceOffset]);
             }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/common/SequenceStorageNodes.java

@@ -1448,19 +1448,19 @@ public final NativeSequenceStorage execute(Node inliningTarget, Object obj, int
 
         @Specialization
         static NativeByteSequenceStorage doByte(byte[] arr, int length, boolean createRef,
-                        @Exclusive @Cached(inline = false) CStructAccess.AllocateNode alloc,
+                        @Shared @Cached(inline = false) CStructAccess.AllocateNode alloc,
                         @Cached(inline = false) CStructAccess.WriteByteNode write) {
-            Object mem = alloc.alloc(arr.length + 1);
+            Object mem = alloc.calloc(arr.length + 1, java.lang.Byte.BYTES);
             write.writeByteArray(mem, arr);
             return NativeByteSequenceStorage.create(mem, length, arr.length, createRef);
         }
 
         @Specialization
         static NativeSequenceStorage doObject(Object[] arr, int length, boolean createRef,
-                        @Exclusive @Cached(inline = false) CStructAccess.AllocateNode alloc,
+                        @Shared @Cached(inline = false) CStructAccess.AllocateNode alloc,
                         @Cached(inline = false) CStructAccess.WriteObjectNewRefNode write) {
-            Object mem = alloc.alloc((arr.length + 1) * CStructAccess.POINTER_SIZE);
-            write.writeArray(mem, arr);
+            Object mem = alloc.calloc(arr.length + 1, CStructAccess.POINTER_SIZE);
+            write.writeArray(mem, arr, length, 0, 0);
             return NativeObjectSequenceStorage.create(mem, length, arr.length, createRef);
         }
     }