From 364ac92baf83f2352f78b718090472639bd92a76 Mon Sep 17 00:00:00 2001 From: Adin Scannell Date: Tue, 23 Jun 2020 23:32:23 -0700 Subject: Support for saving pointers to fields in the state package. Previously, it was not possible to encode/decode an object graph which contained a pointer to a field within another type. This was because the encoder was previously unable to disambiguate a pointer to an object and a pointer within the object. This CL remedies this by constructing an address map tracking the full memory range object occupy. The encoded Refvalue message has been extended to allow references to children objects within another object. Because the encoding process may learn about object structure over time, we cannot encode any objects under the entire graph has been generated. This CL also updates the state package to use standard interfaces intead of reflection-based dispatch in order to improve performance overall. This includes a custom wire protocol to significantly reduce the number of allocations and take advantage of structure packing. As part of these changes, there are a small number of minor changes in other places of the code base: * The lists used during encoding are changed to use intrusive lists with the objectEncodeState directly, which required that the ilist Len() method is updated to work properly with the ElementMapper mechanism. * A bug is fixed in the list code wherein Remove() called on an element that is already removed can corrupt the list (removing the element if there's only a single element). Now the behavior is correct. * Standard error wrapping is introduced. * Compressio was updated to implement the new wire.Reader and wire.Writer inteface methods directly. The lack of a ReadByte and WriteByte caused issues not due to interface dispatch, but because underlying slices for a Read or Write call through an interface would always escape to the heap! * Statify has been updated to support the new APIs. See README.md for a description of how the new mechanism works. PiperOrigin-RevId: 318010298 --- pkg/state/decode_unsafe.go | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) create mode 100644 pkg/state/decode_unsafe.go (limited to 'pkg/state/decode_unsafe.go') diff --git a/pkg/state/decode_unsafe.go b/pkg/state/decode_unsafe.go new file mode 100644 index 000000000..d048f61a1 --- /dev/null +++ b/pkg/state/decode_unsafe.go @@ -0,0 +1,27 @@ +// Copyright 2020 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 state + +import ( + "reflect" + "unsafe" +) + +// unsafePointerTo is logically equivalent to reflect.Value.Addr, but works on +// values representing unexported fields. This bypasses visibility, but not +// type safety. +func unsafePointerTo(obj reflect.Value) reflect.Value { + return reflect.NewAt(obj.Type(), unsafe.Pointer(obj.UnsafeAddr())) +} -- cgit v1.2.3