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authorIan Lewis <ianmlewis@gmail.com>2020-08-17 21:44:31 -0400
committerIan Lewis <ianmlewis@gmail.com>2020-08-17 21:44:31 -0400
commitac324f646ee3cb7955b0b45a7453aeb9671cbdf1 (patch)
tree0cbc5018e8807421d701d190dc20525726c7ca76 /pkg/gohacks
parent352ae1022ce19de28fc72e034cc469872ad79d06 (diff)
parent6d0c5803d557d453f15ac6f683697eeb46dab680 (diff)
Merge branch 'master' into ip-forwarding
- Merges aleksej-paschenko's with HEAD - Adds vfs2 support for ip_forward
Diffstat (limited to 'pkg/gohacks')
-rw-r--r--pkg/gohacks/BUILD12
-rw-r--r--pkg/gohacks/gohacks_unsafe.go57
2 files changed, 69 insertions, 0 deletions
diff --git a/pkg/gohacks/BUILD b/pkg/gohacks/BUILD
new file mode 100644
index 000000000..35683fe98
--- /dev/null
+++ b/pkg/gohacks/BUILD
@@ -0,0 +1,12 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+ name = "gohacks",
+ srcs = [
+ "gohacks_unsafe.go",
+ ],
+ stateify = False,
+ visibility = ["//:sandbox"],
+)
diff --git a/pkg/gohacks/gohacks_unsafe.go b/pkg/gohacks/gohacks_unsafe.go
new file mode 100644
index 000000000..aad675172
--- /dev/null
+++ b/pkg/gohacks/gohacks_unsafe.go
@@ -0,0 +1,57 @@
+// 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 gohacks contains utilities for subverting the Go compiler.
+package gohacks
+
+import (
+ "reflect"
+ "unsafe"
+)
+
+// Noescape hides a pointer from escape analysis. Noescape is the identity
+// function but escape analysis doesn't think the output depends on the input.
+// Noescape is inlined and currently compiles down to zero instructions.
+// USE CAREFULLY!
+//
+// (Noescape is copy/pasted from Go's runtime/stubs.go:noescape().)
+//
+//go:nosplit
+func Noescape(p unsafe.Pointer) unsafe.Pointer {
+ x := uintptr(p)
+ return unsafe.Pointer(x ^ 0)
+}
+
+// ImmutableBytesFromString is equivalent to []byte(s), except that it uses the
+// same memory backing s instead of making a heap-allocated copy. This is only
+// valid if the returned slice is never mutated.
+func ImmutableBytesFromString(s string) []byte {
+ shdr := (*reflect.StringHeader)(unsafe.Pointer(&s))
+ var bs []byte
+ bshdr := (*reflect.SliceHeader)(unsafe.Pointer(&bs))
+ bshdr.Data = shdr.Data
+ bshdr.Len = shdr.Len
+ bshdr.Cap = shdr.Len
+ return bs
+}
+
+// StringFromImmutableBytes is equivalent to string(bs), except that it uses
+// the same memory backing bs instead of making a heap-allocated copy. This is
+// only valid if bs is never mutated after StringFromImmutableBytes returns.
+func StringFromImmutableBytes(bs []byte) string {
+ // This is cheaper than messing with reflect.StringHeader and
+ // reflect.SliceHeader, which as of this writing produces many dead stores
+ // of zeroes. Compare strings.Builder.String().
+ return *(*string)(unsafe.Pointer(&bs))
+}