Fix Go branch for arm64.

This requires several changes:
* Templates must preserve relevant tags.
* Pagetables templates are split into two targets, each preserving tags.
* The binary VDSO is similarly split into two targets, with some juggling.
* The top level tools/go_branch.sh now does a crossbuild of ARM64 as well,
  and checks and merges the results of the two branches together.

Fixes #5178

PiperOrigin-RevId: 351304330

2 files changed, 54 insertions, 0 deletions

diff --git a/pkg/sentry/loader/vdsodata/BUILD b/pkg/sentry/loader/vdsodata/BUILD
new file mode 100644
index 000000000..119199f97
--- /dev/null
+++ b/pkg/sentry/loader/vdsodata/BUILD
@@ -0,0 +1,38 @@
+load("//tools:defs.bzl", "go_add_tags", "go_embed_data", "go_library")
+
+package(licenses = ["notice"])
+
+go_embed_data(
+    name = "vdso_bin",
+    src = "//vdso:vdso.so",
+    package = "vdsodata",
+    var = "Binary",
+)
+
+[
+    # Generate multiple tagged files. Note that the contents of all files
+    # will be the same (i.e. vdso_arm64.go will contain the amd64 vdso), but
+    # the build tags will ensure only one is selected. When we generate the
+    # "Go" branch, we select all archiecture files from the relevant build.
+    # This is a hack around some limitations for "out" being a configurable
+    # attribute and selects for srcs. See also tools/go_branch.sh.
+    go_add_tags(
+        name = "vdso_%s" % arch,
+        src = ":vdso_bin",
+        out = "vdso_%s.go" % arch,
+        go_tags = [arch],
+    )
+    for arch in ("amd64", "arm64")
+]
+
+go_library(
+    name = "vdsodata",
+    srcs = [
+        "vdsodata.go",
+        ":vdso_amd64",
+        ":vdso_arm64",
+    ],
+    marshal = False,
+    stateify = False,
+    visibility = ["//pkg/sentry:internal"],
+)
diff --git a/pkg/sentry/loader/vdsodata/vdsodata.go b/pkg/sentry/loader/vdsodata/vdsodata.go
new file mode 100644
index 000000000..a6dec3b48
--- /dev/null
+++ b/pkg/sentry/loader/vdsodata/vdsodata.go
@@ -0,0 +1,16 @@
+// 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 vdsodata contains a compiled VDSO object.
+package vdsodata