Add in-kernel test runner

This adds a way to run tests inside the Smalltown kernel.

Improvements to the Bazel part of this are tracked in T726

Test Plan: Tested by intentionally failing the test.

X-Origin-Diff: phab/D485
GitOrigin-RevId: e4aad7f28d122d82a7fcb6699e678cbe022e2f73
diff --git a/core/tools/ktest/ktest.bzl b/core/tools/ktest/ktest.bzl
new file mode 100644
index 0000000..03a7d5c
--- /dev/null
+++ b/core/tools/ktest/ktest.bzl
@@ -0,0 +1,61 @@
+#  Copyright 2020 The Monogon Project Authors.
+#
+#  SPDX-License-Identifier: Apache-2.0
+#
+#  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.
+
+"""
+Ktest provides a simple macro to run tests inside the normal Smalltown kernel
+"""
+
+def ktest(deps, tester, initramfs_extra, cmdline):
+    native.genrule(
+        name = "test_initramfs",
+        srcs = [
+            "//core/tools/ktestinit",
+        ] + deps + [tester],
+        outs = [
+            "initramfs.cpio.lz4",
+        ],
+        testonly = True,
+        cmd = """
+        $(location @linux//:gen_init_cpio) - <<- 'EOF' | lz4 -l > \"$@\" 
+dir /dev 0755 0 0
+nod /dev/console 0600 0 0 c 5 1
+nod /dev/null 0644 0 0 c 1 3
+file /init $(location //core/tools/ktestinit) 0755 0 0
+file /tester $(location """ + tester + """) 0755 0 0
+""" + initramfs_extra + """
+EOF
+        """,
+        tools = [
+            "@linux//:gen_init_cpio",
+        ],
+    )
+
+    native.sh_test(
+        name = "ktest",
+        args = [
+            "$(location //core/tools/ktest)",
+            "$(location :test_initramfs)",
+            "$(location //core/tools/ktest:linux-testing)",
+            cmdline,
+        ],
+        size = "small",
+        srcs = ["//core/tools/ktest:test-script"],
+        data = [
+            "//core/tools/ktest",
+            ":test_initramfs",
+            "//core/tools/ktest:linux-testing",
+        ],
+    )
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